Mineral springs of Alaska, with a chapter on the chemical character of some surface waters of Alaska
Explore the source record for details and available documents.
Water Supply Paper↗
SEARCH · Search USGS
Results for “Alaska”
Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Biological investigations in Alaska and Yukon Territory: 1. East-central Alaska; 2. Ogilvie Range, Yukon; 3. Macmillan River, Yukon
Explore the source record for details and available documents.
North American Fauna↗
Fishery resources of waters along the route of the Trans-Alaska pipeline between Yukon River and Antigun Pass in North Central Alaska
No abstract available.
Resource Publication↗
Regional and other general factors bearing on evaluation of earthquake and other geologic hazards to coastal communities of southeastern Alaska
The great Alaska earthquake of March 27, 1964, brought into sharp focus the need for engineering geologic studies in seismically active regions. As a result, nine communities in southeastern Alaska were selected for reconnaissance investigations as an integral part of an overall program to evaluate earthquake and other geologic hazards in most of the larger Alaska coastal communities. This report gives background information on the regional and other general factors that bear on these evaluations. Southeastern Alaska, about 525 miles long and averaging about 125 miles in width, consists of a narrow mainland strip and numerous islands. For the most part, it is a region of rugged relief with numerous glaciers capping many of the higher mountainous areas and with long linear fiords forming the inland waterways. A maritime climate prevails with mild winters and cool summers. The southeastern part of the region receives the highest precipitation in the continental United States. Ketchikan, with a population of 6,994 in 1970, is the largest city. Geology and structure of the area are complex. Igneous, metamorphic, and sedimentary rocks crop out and range in age from Paleozoic to Tertiary. Surficial deposits of Pleistocene and Holocene age mantle many areas. All of southeastern Alaska, except probably the highest peaks, was covered by glacier ice advances of late Pleistocene age. Major deglaciation was well advanced by 10,000 years ago--a time which approximately marks the end of the Pleistocene and the beginning of the Holocene. There followed a period of warm climate called the Hypsithermal, which in southeastern Alaska began 7,000-8,000 years ago and ended about 4,800-3,500 years ago. Glaciers in most places receded back of their present positions. The Hypsithermal was followed by an interval (termed Neoglaciation) of cooler climate and resurgence of glacier ice which continues to the present, although most glaciers are now rapidly receding. During the past 10,000 years worldwide sea level has risen about 100 feet, but during the past 4,000 years it has risen only about 10 feet or about 0.03 inch per year. With sea level used as a datum, the amount of sea-level rise must be added to the apparent uplift of land for the time under consideration to determine the actual amount of land uplift. The widespread presence of emergent marine deposits, several hundred feet above sea level, demonstrates that the land in southeastern Alaska has been uplifted since the last major deglaciation. The greatest known has been uplifted since the last major deglaciation. The greatest known uplift is in the vicinity of Juneau where glaciomarine deposits are present 750 feet above present sea level. Part of southeastern Alaska is presently undergoing one of the most rapid rates of uplift of any place in the world. The fastest emergence is occurring in the Glacier Bay area where the land is being uplifted relative to sea level approximately 3.9 cm per year. Most or all of the uplift appears to be due to rebound as a result of deglaciation. Southeastern Alaska lies within the circum-Pacific earthquake belt, one of the world's greatest zones of seismic activity. During historic time, there have been five earthquakes in the region with magnitudes of 8 or greater, three with magnitudes of 7 to 8, eight with magnitudes of 6 to 7, more than 15 with magnitudes of 5 to 6, and about 140 recorded earthquakes with magnitudes smaller than 5 or of unassigned magnitudes. All of the earthquakes with magnitudes 8 or greater, and a large proportion of the others, appear to be related to the active Fairweather- Queen Charlotte Islands fault system or its western extension, the Chugach-St. Elias fault. Earthquake epicenters on the Denali fault system, the other major fault system in southeastern Alaska, are few in comparison. However, because high microearthquake activity has been recorded recently on this system and earthquakes of moderate size have occurred on some of its segments, the Denali fault system probably should not be dismissed as a relict fault system of no current tectonic importance. There are numerous other known faults, as well as lineaments that may be faults of varying degrees of tectonic activity in southeastern Alaska, adjacent Canada, and eastern Alaska. One of these elements is the Totschunda fault system, which connects with the Denali fault system in eastern Alaska; it has been very active during Holocene time but few historical earthquake epicenters appear to be related to it. Both historical seismicity and geologic conditions, such as frequency and recency of faulting, must be considered together to permit an assessment of the future earthquake probability of an area. Data are too few for both factors for an accurate evaluation to be made of earthquake probability in southeastern Alaska. However, information compiled in the form of strain-release and seismic-zone maps permit some generalizations. Thus, it is tentatively concluded that most, if not all, of southeastern Alaska should be placed in seismic zone 3, a zone in which earthquakes of magnitude greater than 6 will occur from time to time and where there may be major damage to manmade structures. Inferred effects from future earthquakes in southeastern Alaska include: (1) surface displacement along faults and other tectonic land-level changes, (2) ground shaking, (3) compaction, (4) liquefaction in cohesionless materials, (5) reaction of sensitive and quick clays, (6) water-sediment ejection and associated subsidence and ground fracturing, (7) earthquake-induced sub aerial slides and slumps, (8) earthquake induced subaqueous slides, (9) effects on glaciers and related features, (10) effects on ground water and stream flow, and (11) tsunamis, seiches, and other abnormal water waves. Because of the reconnaissance nature of our studies in the coastal communities and the sparsity of laboratory data on physical properties of geologic units in each area studied, the inferred effects must be largely empirical and generalized. Therefore, the inferences are based in large part upon the effects of past major earthquakes in Alaska and elsewhere, particularly upon the well-documented effects of the Alaska earthquake of March 27, 1964. Buildings, highways, bridges, tunnels, harbor facilities, pipelines, canals, and other manmade structures may be severely damaged or destroyed by fault displacement or related tectonic land-level changes in southeastern Alaska. Direct damage from fault rupture would be restricted virtually to structures built directly athwart the fault. In California and Nevada, fault rupture almost always accompanies shocks of magnitude 6.5 or greater. The Alaska earthquake of March 27, 1964, and the Chilean earthquake of May 22, 1960, dramatically illustrated the severe adverse effects that can result from uplift or subsidence over a wide area. The variable most responsible for the degree of shaking at any epicentral distance is the type of ground. Generally, shaking is considerably greater in poorly consolidated deposits than in hard bedrock, particularly if the deposits are water saturated. Severe shaking of alluvial deposits and manmade fill, with resultant heavy damage, is well documented from the records of many past earthquakes. Damage commonly has been heavy as a result of ground settlement caused by compaction of loose sediments by shaking during an earthquake. This has been especially true where compaction was accompanied by tectonic downdrop of land, such as occurred during the Chilean earthquake of 1960 and the Alaska earthquake of 1964. Loosely emplaced manmade fill, deltaic deposits, beach deposits, and alluvial deposits may be susceptible to compaction in southeastern Alaska during a severe earthquake. Liquefaction of sand and silt is a fairly common effect of large earthquakes. It was well illustrated at Niigata, Japan, during the earthquake of June 16, 1964, and resulted in extensive damage. When part of a sloping soil mass liquefies, the entire mass can undergo catastrophic failure and can flow as a high-density liquid. In southeastern Alaska, deltaic deposits probably would be most susceptible to liquefaction. Sensitive and quick clays, which lose a considerable part of their strength when shaken, commonly fail during an earthquake and become rapid earthflows. Extensive studies were made of the sensitivity of the Bootlegger Cove Clay at Anchorage because of the marked loss of shear strength and dramatic failures of the deposits during the Alaska earthquake of 1964. If similar sensitive clays are present in some places in southeastern Alaska, they most likely are in some of the emergent fine-grained marine deposits; supporting data to confirm their presence, however, are largely lacking. Records of some 50 major earthquakes show that in at least half of the instances water and sediment have been ejected from surficial deposits Water-sediment ejection and associated subsidence and ground fracturing commonly cause extensive damage to the works of man. Ejecta may fill basements and other low-lying parts of buildings. Agricultural land can be covered with a blanket of infertile soils, and small ponds can be filled or made shallow. In southeastern Alaska these phenomena are most likely to occur on valley floors, deltas, tidal flats, alluvial fans, swamps, and lakeshores. Earthquake-induced sliding on land generally is confined to steep slopes but may take place in fine-grained deposits on moderately to nearly flat surfaces if the deposits are subject to liquefaction. A large rockslide triggered by the Lituya Bay, Alaska, earthquake of July 10, 1958, generated a wave that surged up the opposite wall of the inlet to a record height of 1,740 feet. During the Hebgen Lake, Montana, earthquake of August 17, 1959, a spectacular rockslide plunged into the Madison River canyon, buried 28 people, dammed the river, and created a large lake. Earthquake-records are replete with accounts of sliding of surficial deposits during moderate to large earthquakes. Most or all of the general factors that favor subaerial landsliding are present in southeastern Alaska. Earthquake-induced subaqueous slides can produce adverse effects both nearshore and some distance offshore. Nearshore sliding may progress shoreward and destroy harbor facilities and other structures, commonly with substantial loss of life. Disastrous large submarine slides occurred along the fronts of deltas in Seward and Valdez during the Alaska earthquake of 1964. In similar fashion, the largest submarine slides in southeastern Alaska likely will be triggered along the larger delta fronts. Sliding farther offshore can constitute a threat to navigation because of changes in water depths. Also underwater sliding can break communication cables. Glaciers were not greatly affected by the Alaska earthquake of 1964 despite the fact that about 20 percent of the area that underwent strong shaking is covered by ice. In contrast, the cataclysmic avalanche of ice and rock that fell from a high glacier-covered peak in Peru during the earthquake of May 31, 1970, produced devastating effects downvalley on man and his works in the form of mudflows. Most towns in southeastern Alaska are sufficiently distant from glaciers so as not be to directly affected. Both the Alaska earthquake of 1964 and the Hebgen Lake, Montana, earthquake of 1959 significantly affected ground- and surface-water regimens. Water levels in some wells declined whereas in others flow increased. Some springs discharged at a rate three times as much as normal; flow of others decreased or stopped. Discharge of many streams increased markedly. Most or all of the effects described above could occur in parts of southeastern Alaska during future large earthquakes. Tsunamis, seiches, and other abnormal water waves associated with large earthquakes commonly cause vast property damage and heavy loss of life. Tsunami effects can be devastating to coastal areas as far as many thousands of miles from their generation source. Seiche effects generally are confined to inland bodies of water or to relatively enclosed coastal bodies of water. Abnormal waves generated by submarine sliding or by subaerial sliding into water generally produce only local effects but may be highly devastating. Tsunami waves resulting from the Chilean earthquake of 1960 inflicted extensive damage and loss of life on coastal communities throughout a large part of southern Chile, and significant runups and damage were recorded in many places throughout the Pacific Ocean area. The tsunami waves generated by the Alaska earthquake of 1964 struck with devastating force along a broad stretch of the Alaska coast and produced heavy property damage and loss of life as far away as Crescent City, Calif. Seiche waves generated by that earthquake reached runup heights of 20-30 feet on some lakes in Alaska, and water-level fluctuations were recorded on streams, reservoirs, lakes, and swimming pools in States bordering the Gulf of Mexico. Waves generated by submarine sliding struck violently at a number of places during or immediately after the quake and were the major cause of loss of life and damage to property. Slide-generated waves probably would have a higher destructive potential in southeastern Alaska than either tsunami waves or seiche waves because of their possibly higher local runups and because they can hit the shores almost without warning during or immediately after an earthquake. Nonearthquake-related geologic hazards, although generally far less dramatic than those related to earthquakes, tend to occur so much more frequently or persistently that their aggregate effects can be significant. Three kinds of geologic hazards of this type are discussed: (1) nonearthquake-induced landsliding and subaqueous sliding, (2) flooding, and (3) land uplift. The potential for nonearthquake-triggered landsliding in southeastern Alaska ranges widely from place to place. Past sliding generally furnishes the clue in the prediction of where and in what materials future sliding will occur. Fast-moving rockslides, debris slides, and mudflows can be expected to occur from time to time on steep slopes and be highly destructive to highways, power plants, pipelines, buildings, and other facilities located on a slope or at its base. Present slow downslope movement of talus can be expected to continue at the same general rate unless conditions are changed by man or there are climatic changes. Snow and debris avalanches can be especially hazardous during winter months. Long-inactive landslides may be triggered into renewed activity or new slides may be created by man-induced modifications. Accelerated slope erosion and debris flows may follow large-scale clearing and cutting of timber. Subaqueous sliding can be expected to occur periodically along fronts of deltas and on other oversteepened underwater slopes. Floods have been common in parts of southeastern Alaska because of heavy precipitation and rapid runoff from steep slopes with resulting heavy damage to roads and other facilities. Continued damage can be expected in the future unless more remedial measures are taken. Current uplift of land in southeastern Alaska, although probably not affecting man significantly in a short period of time, may have some adverse long-term effects. These long-term effects should be borne in mind when facilities such as docks and boat harbors are constructed on or near the shore, where there is a critical relation between height of land and water.
Alaska↗
Geology of possible petroleum provinces in Alaska
The history of petroleum exploration in Alaska and the geology of possible petroleum provinces in Alaska are reviewed. Maps showing Alaska's major Mesozoic and Tertiary tectonic elements, possible petroleum provinces, and indications of petrol, are included in this report. Annotated references in Geological Survey publications relating to petroleum and oil shale in Alaska are given at the end of the report. For the purpose of appraising its petroleum possibilities, Alaska is divided into the southern, central, and northern major geologic-physiographic regions. Southern Alaska includes the arcuate mountain chain formed by the Alaska and Aleutian Ranges and the Mentasta- Nutzotin Mountains, the coastal range and valley area to the south, and the southeastern Alaska "panhandle" -- an area of 185,000 square miles. Oil seeps on the west shore of Cook Inlet in southern Alaska were known as early as 1853, and claims were staked in this region in 1882. Drilling began near the oil seeps in the Katalla district about 1901, and this started Alaska's first period of oil activity. From 1902 to 1933 the Katalla field produced 154,000 barrels of oil from fractured shale and sandstone of Tertiary age the- first and only commercial production in Alaska. On the basis of geology, surficial indications of petroleum, and test wells drilled, six possible petroleum provinces are indicated in southern Alaska. They are Heceta Island area, Keku Islands area, Cook Inlet Mesozoic province, Gulf of Alaska Tertiary province, Cook Inlet Tertiary province, and Copper River basin. The exposed rocks in the Heceta Island area include lower Paleozoic graywacke-type sandstone, sandstone, conglomerate, and massive limestones with reeflike structures; igneous rocks are rare or lacking in much of the area. The Kosciusko-Tuxekan-Heceta synclinorium, the main structural feature, is modified by minor folds and faults. Some of the minor folds are reported to be broad and open, with flanks dipping 20°-145°. As far as known, the Heceta Island area has not heretofore been seriously considered as a possible petroleum province. Rocks of Silurian to Cretaceous age are exposed in the Keku Island area and include moderately folded and relatively unaltered limestone and other marine sedimentary rocks. The Cook Inlet Mesozoic province, a land area of approximately 18,500 square miles, includes a great thickness of unmetamorphosed marine sedimentary rocks of Jurassic and Cretaceous age. At least 23 test wells were drilled or started in this province by the end of 1955. Shows of oil and gas were encountered in many of these wells. During 1955 at least ten oil companies were active in this area and by the end of 1955 about 1 1/2 million acres were included in oil and gas leases applied for or granted. The Gulf of Alaska Tertiary province includes about 5,200 square miles in which rocks of Tertiary age are exposed or are believed to underlie Quaternary deposits. Between 1901 and the end of 1955 about 47 wells were drilled or started in this province. The Cook Inlet Tertiary province embraces an area of about 9,500 square miles, of which about 4,100 is covered by the shallow waters of Cook Inlet. Petroleum exploration has been in that part of the area which overlaps the Cook Inlet Mesozoic province. Eocene or younger Tertiary nonmarine sedimentary rocks are believed to underlie much of the province, and marine rocks of Tertiary age may also be present. The Copper River basin is a topographic basin underlain by unconsolidated deposits of Quaternary age. Tertiary rocks favorable for the accumulation of petroleum may underlie part of the basin but this is not believed likely. Except for some leasing activity no petroleum exploration has been recorded in the Copper River Basin to the end of 1955. Central Alaska is a region of about 275,000 square miles and consists of an irregular assemblage of intricately dissected uplands and alluvium-floored lowland basins. Scattered peaks of resistant intrusive igneous rocks surmount most of the upland areas. In the vast region of central Alaska only six test wells are known to have been drilled for the purpose of finding oil and gas. The maximum depth reached was 350 feet and the holes were mostly or entirely in Quaternary deposits. In recent years several oil companies have investigated some parts of the region and large areas in the Yukon-Koyukuk province are now under lease. Oil seeps, gas seeps, and other indications of petroleum have been reported from many localities; samples from two localities have been analyzed and reported to be petroleum. The geology of central Alaska is similar in a general way to that of the area between the Rocky Mountains and Sierra-Cascade belts of the United States. Sedimentary rocks, probably equivalent to the Precambrian Belt series, and rocks of the Cambrian and all younger geologic systems have been recognized in central Alaska. The structure of the region is known to be complex, but except in local mineral districts, it has not been mapped in detail. Based on the limited amount of available information, the region cannot be regarded as distinctly favorable for significant accumulations of petroleum. However, three pre-Cenozoic provinces, the Yukon-Koyukuk, the Kobuk, and the Kandik, and several large Cenozoic basin provinces may be worthy of further investigation. Northern Alaska includes the Brooks Range and all the treeless tundra north to the Arctic Coast, an area of about 125,000 square miles. The presence of oil seeps along the Arctic Coast has been known at least since 1900 and a description of the Cape Simpson oil seeps vas published in 1909. Since then oil and gas seeps have been described from nine localities, and oil shales and oil-bearing sandstones are known from many localities in the Arctic Foothills province. Oil and gas deposits have been discovered and geologic conditions are favorable for oil and gas accumulations in approximately half of the region. In 1923 approximately 37,000 square miles in northern Alaska was reserved by Executive order as Naval Petroleum Reserve No. 4. In 1944 the U. S. Navy began a vast petroleum exploration program which was suspended in 1953. In the years 1945 through 1955, 37 test wells and 45 core tests were drilled on 18 structures. Three oil fields, Umiat, Simpson, and Fish Creek, and two gas fields, South Barrow and Gubik, were discovered. Total reserve estimates for all discoveries of oil to 1955 range from 30 to 100 million barrels, and for gas, from 370 billion to 900 billion cubic feet. All northern Alaska, with the exception of the Brooks Range, can be considered a possible petroleum province, but the region can be subdivided into provinces of somewhat different potentialities. These subdivisions roughly correspond with the geomorphic provinces and sections, which in turn reflect differences in geology. The known oil-bearing beds are of Mesozoic age, primarily Cretaceous, and thus the possible petroleum provinces could be designated as Mesozoic. However, Paleozoic and Cenozoic rocks with favorable reservoir characteristics are exposed in the region and possibly underlie, in favorable structural situations, some of the areas as yet not tested. The Arctic Coastal Plain province includes gently folded and flat-lying Mesozoic beds that overlie a basement complex of Paleozoic and early Mesozoic age. Near the southern edge of this province the basement rocks are at depths of at least 20,000 feet, and to the north these rocks rise to within 2,500 feet of the surface. The Teshukpuk Lake section of the Arctic Coastal plain includes many of the known oil seeps; it is the most accessible to sea transportation, and lies almost completely within NPR 4. Thirteen test wells and 35 core tests have been drilled here; one gas field and two (at present, noncommercial) oil fields have been discovered. The possibility of further discoveries may depend largely on locating porous sandstones in stratigraphic rather than anticlinal traps. The White Hills section is distinguished topographically from the Teshukpruk section by its white-gravel-covered hills and fever lakes, and geologically by the presence of Tertiary rocks, including 2,000 feet of nonmarine beds in the west and at least 7,000 feet of marine beds to the east, in the vicinity of Carter Creek. This section appears to be more complex structurally. No test wells have been drilled in the White Hills section. The Northern Foothills section includes many closed anticlines. Twenty-four test wells and ten core tests have been drilled on 11 structures and two discoveries have been made -the Umiat oil field and the Gubik gas field. All these tests have been drilled in Cretaceous rocks. The Southern Foothills section is structurally similar to the Alberta Foothills and to the northern part of the Brooks Range. Great thicknesses of marine shale of Lover Cretaceous, Jurassic, and Triassic age are exposed. The outcropping Mesozoic sandstones are generally poorly sorted, nonporous, and impermeable. To the south the section is bordered by mountainous exposures of Mississippian limestone, which probably underlie at least part of this section. The rocks that underlie the deeply eroded complex structures of the Brooks Range include schist, slate, argillite, and limestone. Some exposed limestones have a strong petroleum-like odor and contain traces of petroleum residues.
Alaska↗
Time-slice maps showing age, distribution, and style of deformation in Alaska north of 60° N.
The structural architecture of Alaska is the product of a complex history of tectonism that occurred along the Cordilleran and Arctic margins of North America through interactions with ancient and modern ocean plates and with continental elements derived from Laurentia, Siberia, and Baltica. To unravel the tectonic history of Alaska, we constructed maps showing the age, distribution, structural style, and kinematics of contractional and penetrative extensional deformation in Alaska north of latitude 60° N. at a scale of 1:5,000,000. These maps use the Geologic Map of the Arctic (Harrison and others, 2011) as a base map and follow the guidelines in the Tectonic Map of the Arctic project (Petrov and others, 2013) for construction, including use of the International Commission on Stratigraphy time scale (Cohen and others, 2013) divided into 20 time intervals. We find evidence for deformation in 14 of the 20 time intervals and present maps showing the known or probable extent of deformation for each time interval. Maps and descriptions of deformational style, age constraints, kinematics, and information sources for each deformational episode are discussed in the text and are reported in tabular form. This report also contains maps showing the lithologies and structural geology of Alaska, a terrane map, and the distribution of tectonically important units including post-tectonic sedimentary basins, accretionary complexes, ophiolites, metamorphic rocks. These new maps show that most deformational belts in Alaska are relatively young features, having developed during the late Mesozoic and Cenozoic. The oldest episode of deformation recognized anywhere in Alaska is found in the basement of the Farewell terrane (~1.75 Ga). Paleozoic and early Mesozoic deformational events, including Devonian deformation in the Arctic Alaska terrane, Pennsylvanian deformation in the Alexander terrane, Permian deformation in the Yukon Composite (Klondike orogeny) and Farewell terranes (Browns Fork orogeny), Early and Late Jurassic deformation in the Peninsular-Wrangellia terranes, and Early Cretaceous deformation in northern Alaska (early Brookian orogeny) show that within-terrane amalgamation events occurred prior to assembly of Alaska. Widespread episodes of deformation in the Late Cretaceous and early Cenozoic, in contrast, affected multiple terranes, indicating they occurred during or following the time of assembly of most of Alaska. The primary deformational event in northern Alaska was the Late Jurassic and Early Cretaceous (early) Brookian orogeny, which affected most terranes north and west of the early Cenozoic Tintina, Victoria Creek, Kaltag, and Poorman dextral-slip faults in central Alaska. In southern Alaska, formation of the southern Alaska accretionary complex (Chugach, Prince William, Yakutat terranes) and associated magmatism in the Peninsular-Wrangellia terrane began near the Triassic-Jurassic boundary and continued episodically throughout the remainder of the Mesozoic and the Cenozoic. The collision of these terranes with the Farewell and Yukon Composite terranes in central Alaska is recorded by contractional deformation that emanated from the intervening basins in the Late Cretaceous. The boundary between northern and central Alaska is constrained to late Early Cretaceous but is enigmatic and not obviously marked by contractional deformation. Early Cenozoic shortening and transpressional deformation is the most widespread event recorded in Alaska and produced the widespread late Brookian orogenic event in northern Alaska. Middle and late Cenozoic shortening and transpression is significant in southern Alaska inboard of the underthrusting Yakutat terrane at the Pacific margin subduction zone as well as in northeastern Alaska.
Alaska↗
The geography and geology of Alaska; a summary of existing knowledge, with a section on climate, and a topographic map and description thereof
Alaska, the largest outlying possession of the United States, is that great land mass forming the northwestern extremity of the North American continent, whose western point is within 60 miles of the Asiatic coast (PI. II). About one-quarter of this area lies within the Arctic Circle, and from the standpoint of geographic position must be regarded as an arctic province; but the southern seaboard, exposed to the warm winds and waters of the Pacific, gives to the entire southern portion of the territory" a comparatively warm climate. It is not generally realized that the range of climate in Alaska is greater than that between Florida and Maine. At the southernmost point of the Pacific coast the mean annual temperature is not far from that of the city of Washington, the winters being warmer and characterized by less snowfall; the Yukon Valley on the other hand has a winter climate similar to that of northern Montana and Dakota; while in the extreme northern part of the territory the meteorologic conditions are invariably arctic. Though as yet only sparsely settled, Alaska's vast area and great resources make it one of the most important possessions of the United States and promise its rapid development. During the years 1890 to 1900 the population increased from 32,052* to 63,592. The mineral output, which in 1890 was valued at less than $800,000, exceeded $9,000,000 in 1904, and the fisheries show a corresponding growth. This rapid development has attracted public attention and led to urgent demand for explorations, surveys, and other investigations. So actively has this work been pushed, both by public and private enterprise, that exact knowledge of the geography, geology, and mineral resources of the interior has made greater strides within the last eight years than during the preceding thirty-one years since the acquisition of Alaska. The facts regarding the geography and geology, scattered as they are through the many books and reports of this period, are not always readily accessible, and the time seems ripe to present them in a summarized form. The topography of Alaska is varied and complex (see PI. I), and it is not easy to present briefly even the salient features. The limited number of pages here devoted to the subject precludes the possibility of detailed treatment, even if the facts were available. Much of the description has been taken from the results attained by other investigators, the writer being personally familiar with only a part of this large province. A list of the publications consulted is appended. The larger geographic features of Alaska are now fairly well known, though the detailed surveys which are demanded by the development of many localities have hardly been begun. Preliminary surveys have been completed of all but three 8 of the larger rivers. The most important mountain ranges have been at least outlined (fig. 3). Only three large areas remain almost entirely unmapped: One in southwestern Alaska, between Cook Inlet and the lower Kuskokwim, and the others in northern Alaska, embracing the Arctic watershed east and west of the Colville River. Nearly all the surveys of the interior, however, have been of a preliminary and exploratory character, and to meet the requirements of exact geography must be followed by more detailed mensuration. Though the coast line has been fairly well known for more than half a century, knowledge of the interior has been gained chiefly within the last two decades. This has not yet found its way into text-books and has too often been entirely ignored by cartographers. If facts are presented which may seem elementary, it is because even well-informed people have been known to harbor misconceptions in regard to the orographic features, climate, and general character of Alaska. Those who read of the perils and privations of winter travel and explorations are apt to picture a region of ice and snow; others, again, who have personal knowledge of the tourist route of southeastern Alaska, regard the whole district as one of rugged mountains and glaciers. In point of fact, glaciers are now nearly limited to the ranges bordering the Pacific and to the two slopes of the Alaska range; and even during the greatest development of glaciers but a small portion of Alaska was under ice (see map, PI. XXII). As a treatise on geography would hardly be complete without some discussion of the climate, meteorologic data have been compiled by Mr. Cleveland Abbe, jr., but the discussion of this does not pretend to be more than a cursory treatment of the subject. The scope of the paper seems to require also a brief summary of the development of geographic knowledge of Alaska. This subject, with its many ramifications, is of fascinating interest and offers a magnificent field for the trained historian. If the accompanying sketch of discovery and exploration awakens any measure of popular interest the writer will feel amply rewarded for having attacked a theme which hardly falls within the scope of his investigations. When this compilation was begun it was intended to be chiefly a description of the topography of Alaska, as illustrated by the accompanying map (PI. XXXIV, in pocket), which was compiled under the direction of the late R. U. Goode. In the course of the work there accumulated much geologic as well as geographic material which seemed worthy of inclusion in the report. As no comprehensive statement of the geology of Alaska has been made since the modern epoch of investigation was begun, an attempt will be made to give a summary of all results achieved. Since the writer has obtained much of his knowledge of the facts from the work of others, he disclaims any pretense of making an entirely original contribution to geologic science. He feels, however, that a personal familiarity with a considerable part of the province, gained during seven consecutive seasons of field work, will justify Mm in presenting conclusions which may in some cases be at variance with those in the reports on which he must draw for his facts. Throughout this report attempt will be made to credit borrowed material to the source from which it is drawn. Where such matter has been obtained entirely from published reports there is no difficulty in so doing; but as regards investigators of the Geological Survey, with whom the writer has collaborated both in field and in office, the case is somewhat different, for it is not always possible to know whether this or that theory originated with the writer or with one of his colleagues. It will, then, perhaps suffice to state that this report could not have been prepared without the explorations and researches of the geologists, F. C. Schrader, Walter C. Mendenhall, Arthur J. Collier, J. E. Spurr, and Arthur C. Spencer; and the surveys of the topographers, T. G. Gerdine, D. C. Witherspoon, D. L. Reaburn, W. J. Peters, and E. C. Barnard. Each of these men, in the course of from two to six years of field work, has made important contributions to the knowledge of the geography and geology of Alaska, and not all of these results have yet been put in print. In the last season (1903) L. M. Prindle, C. W. Wright, Arthur Hollick, G. C. Martin, F. L. Hess, and Fred H. Moffit have carried on geologic work in Alaska, and the writer has made use of their work now in course of publication. He has also been fortunate in having access to the manuscript reports of Walter C. Mendenhall and F. C. Schrader on the Copper River basin, to which references will be made. The matter here presented should be credited in a measure to all of these investigators, but for many of the theories advanced the writer alone is responsible. As this manuscript goes to press there has been opportunity to incorporate some of the results of the field work of 1904. As far as possible these have been embodied in the text, but in some instances it has been found advisable to add them only as footnotes. During the past summer F. E. and C. W. Wright extended the geologic reconnaissance in southeastern Alaska. In southwestern Alaska G. C. Martin and T. W. Stanton have determined the general Mesozoic section, while F. H. Moffit has made a reconnaissance of the northern part of the Kenai Peninsula. A. J. Collier has mapped the geology of the Cape Lisburne region, and L. M. Prindle and F. L. Hess have made contributions to the knowledge of the metamorphic terranes of the Yukon-Tanana district. It is the writer's purpose to describe in nontechnical language the larger geographic features and discuss their relation as far as the data available will permit. In the treatment of the geology, however, less effort will be made to make the matter acceptable to the lay reader. It is hoped, however, that a brief summary of the salient features of the geologic history' may be not without interest to the general public. If this paper serves in some measure to dispel the popular fallacies regarding Alaska and to disseminate more accurate knowledge of its geographic and geologic features, the purpose of its publication will be accomplished.
Alaska↗
Phase 1 technical implementation plan for the expansion of the ShakeAlert earthquake early warning system to Alaska
Executive Summary The conference report accompanying the fiscal year (FY) 2022 Consolidated Appropriations Act (Public Law 117–103) for the U.S. Department of the Interior and related agencies directed the U.S. Geological Survey (USGS) to “work with the State of Alaska to develop an implementation plan to be completed within two years in order to put ShakeAlert/Earthquake Early Warning in Alaska” (p. 29). Congress included $1 million in the FY 2022 appropriation to conduct this effort. The USGS Earthquake Hazards Program, along with partner organizations, has developed the ShakeAlert earthquake early warning (EEW) system for the West Coast, which currently operates in California, Oregon, and Washington. The purpose of the system and its alert delivery partners is to reduce the impact of earthquakes and save lives and property by delivering ShakeAlert-powered alerts that are transmitted to the public via mass notification technologies, and by providing more detailed data streams to institutional users and commercial service providers to trigger automated, user-specific, protective actions. ShakeAlert was designed in such a way that it could be expanded to other U.S. regions with high earthquake risk, after the build-out of seismic and geodetic networks to support ShakeAlert in a specified region is completed and the necessary funding is secured for long-term operation and maintenance. When an earthquake occurs, seismic waves radiate from the rupturing fault like waves on a pond. It is these waves that people feel as earthquake shaking and that can cause damage to structures. Using networks of ground-motion sensors and sophisticated computer algorithms, ShakeAlert can detect an earthquake seconds after it begins, calculate its location and magnitude, and estimate the resulting intensity of shaking. Early warnings of impending shaking are then sent to people and systems that may experience damaging shaking, allowing them to take appropriate protective actions. Depending on the user’s distance from the earthquake, alerts may be delivered before, during, or after the arrival of strong shaking. There will almost always be a region near the earthquake epicenter where alerts arrive after damaging shaking has begun. The ShakeAlert system updates its ground-motion estimates as an earthquake grows larger. In response to the FY 2022 congressional direction, the USGS worked with the State of Alaska to devise this implementation plan for ShakeAlert expansion to Alaska. The USGS engaged with the Alaska Division of Homeland Security and Emergency Management (DHS&EM) and the Alaska Division of Geological and Geophysical Surveys (DGGS). A cooperative agreement was awarded to the Alaska Earthquake Center (AEC) at the University of Alaska Fairbanks (UAF) for their contributions to the plan and their work coordinating with other networks in Alaska. The USGS engaged with the Alaska Seismic Hazards Safety Commission (ASHSC) throughout the process. The USGS also held a series of Alaska stakeholder engagements. The process of developing the implementation plan was facilitated by contracted staff from Corner Alliance, which is a government consulting firm. This implementation plan describes the details and estimates the costs for a Phase 1 expansion of the ShakeAlert system to Alaska. A geographically limited Phase 1 goal was chosen that covers the highest risk and most populated areas of Alaska. The areas proposed encompass the State’s main population centers and 90 percent of the State’s population. This Phase 1 design is considered very challenging and ambitious from the viewpoint of network operators. The lessons learned if this plan is implemented could be used to consider subsequent phases to expand EEW beyond Phase 1 in Alaska in the future. ShakeAlert is built on the foundation of the sensor networks and data processing infrastructure of the USGS-led Advanced National Seismic System (ANSS). This implementation plan calls for a total of 450 high-quality, real-time EEW-capable ANSS seismic stations in Alaska: 270 new stations, 160 upgraded stations, and 20 existing stations. These seismic station numbers are based on a station spacing of 10 kilometers (km) in urban areas, 20 km in seismic source areas that endanger population centers, and 40 km in other areas. The associated costs also include support for some EEW-capable global navigation satellite system (GNSS) stations, with a focus on improving warnings for large subduction zone earthquakes. For effective EEW, ShakeAlert requires low-latency, high-availability, robust telemetry links to deliver continuous, real-time data from field stations to the data centers. The Alaska data processing hardware infrastructure would follow the general design for fail-safe operation that is used for the ShakeAlert system on the West Coast. The ShakeAlert architecture uses two independent layers: the production layer for earthquake processing and the alert layer to make alerting decisions and serve alerts to users. This implementation plan includes two geographically separated data centers in Alaska, each with two fully independent production and alert layers using the same system design developed for the West Coast. As of March 2024, the ShakeAlert system is at version 3.0.1, with more advanced versions in the development and testing pipeline. ShakeAlert originally used two algorithms to determine the location and magnitude of earthquakes using seismic data. A third algorithm that can calculate very large magnitudes of very large earthquakes with geodetic data was added in March 2024. ShakeAlert publishes several data and alert products to meet the needs of different users. All messages include the location of the earthquake, either as a point or a line, and its magnitude. Ground-shaking estimates are published in two forms, as ground-motion contours and a map grid. Providing adequate warning time for strong shaking (the “target threshold”) requires sending alerts at a threshold lower than that strong shaking level (the “alert threshold”). The thresholds for public alerting in Alaska would be a joint USGS and State decision. To have the greatest benefit, ShakeAlert-powered alerts would be delivered to institutional users and individuals by all practical pathways. The USGS alert layer can support thousands of institutional users and alert redistributors, but the USGS does not have the mission nor the infrastructure and expertise to perform mass notifications to the public or implement automatic actions for end users of the alerts. To meet this need, ShakeAlert recruits private sector “technology enablers” that have the necessary expertise to develop end-user implementations using EEW alerts with the goal of stimulating an EEW industry. Earthquake early warning alerts are useless if people do not know how to respond to them. Although the alert messages include instructions about what to do (drop, cover, and hold on), alerts are more effective if people have been trained in advance. Messages about ShakeAlert’s capabilities, limitations, and benefits could be integrated with existing earthquake education programs, including State-run programs. Therefore, ShakeAlert would coordinate with both public and private partners and stakeholders through various partnerships and agreements to accomplish consistent and ongoing public earthquake hazard education. The estimated capital cost of completing the computing infrastructure and sensor networks for the Phase 1 ShakeAlert expansion to Alaska is approximately $66 million in 2024 dollars. The annual operation and maintenance cost of the completed system is estimated to be $12 million per year in 2024 dollars when fully built out.
Alaska↗
Modeling, mapping, and measuring the risk of freshwater invasive species across Alaska
Freshwater ecosystems of the Alaskan Arctic and Subarctic provide resources that are culturally, ecologically, and economically invaluable. Presently, these regions are relatively free of the impacts from invasive species compared to southern latitudes. To date, there have been relatively few verified introductions of aquatic invasive species (AIS) to freshwater ecosystems in Alaska. The expanding list and distribution of AIS has led to significant negative ecological and economic impacts (e.g., waterweed Elodea nuttalli ; E. canadensis and northern pike Esox Lucius introduced outside its native range in Alaska). Escalating human activity across Alaskan lands and waters, coupled with rapidly shifting environmental conditions, increases the potential for new species introductions and subsequent establishment. Creating a proactive framework for well-informed decision-making and action can improve the effectiveness of prevention efforts and bolster decision support tools that help resource managers direct limited resources. Prioritizing AIS that may be introduced and become established, as well as the locations at highest risk of invasion, is foundational to building a proactive invasive species management framework in Alaska. This project sought to identify and prioritize AIS known to be invasive in the contiguous United States, evaluate current and future habitat suitability for AIS in Alaska, and assess potential for AIS to be transported to habitats across Alaska, utilizing similar assessment methods as implemented for Bering Sea marine invasive species and non-native plants in Alaska. To accomplish this goal, the objectives of the project were to: 1) develop a formal ranked list of potential AIS to freshwater systems of Alaska; 2) assess the level of establishment risk for potential AIS by developing habitat suitability models for waterbodies across Alaska; and 3), identify potential pathways and specific vectors for high-risk AIS to invade Alaska and develop a framework for how vector analysis will be completed to understand transport risk. Overall, our goal is horizon scanning which is defined by Roy et al. (2019) as “a systematic examination of potential threats and opportunities, within a given context, and likely future developments, which are at the margin of current thinking and planning.” The scans include pathway analyses and risk screening of species present at pathway origin points, with a focus on identifying species at high risk of being introduced, becoming established, spreading, and causing harm. We refined a list of 28 AIS from a list of hundreds based on characterizations of species’ invasiveness and species’ proximity to Alaska (USGS 2020; GBIF 2022). Next, we evaluated the relative invasiveness of individual species to create an initial AIS ranking. We sought to characterize habitat suitability of AIS by selecting variables that were continental in scale, covering North America to include Alaska as well as the lower 48 states comparing natural discharge, sub-basin average terrain slope (degrees), average silt fraction, average organic carbon, lithological class, and human footprint in sub-basin in 2009. We estimated AIS habitat suitability across the entire state of Alaska using the physiological tolerances of the AIS (Appendix 2). We also evaluated pathways and vectors for the introduction of AIS (Appendix 2). Many pathways and vectors considered did not meet the criteria for Alaska or freshwater systems. Of the 28 ranked species that we categorized as very high, high, and moderate levels of invasiveness; all three risk groups included fish and mollusks (Appendix 2). One commonality of the very high-invasiveness-ranked species was the availability of Ecological Risk Screening Summary documents (USFWS, 2022) produced by U.S. Fish and Wildlife Service (USFWS), except for the goldfish ( Carassius auratus ) and the New Zealand mudsnail ( Potamopyrgus antipodarum ). The Ecological Risk Screening Summary is now available for New Zealand mudsnails. In general, fish species often ranked very high or high in invasiveness and included sportfish and aquarium fish, suggesting the importance of pathways such as aquarium trade, fishing industry, intentional (but illegal) introductions of sportfishes and aquarium fishes for establishment. The technique we used for habitat suitability models necessitated aquatic environmental datasets that were continental in scale, which was often interpolated from very coarse resolution source data layers, particularly in Alaska. Better spatial data representing aquatic environments would likely improve this approach. While the lack of introductions in Alaska and nearby provinces and states is encouraging, the lack of occurrence data for the focal species also created complications for habitat suitability modeling. Despite the challenges, the habitat suitability models indicated limited suitability for warmwater species while some species, such as Brook trout (S alvelinus fontinalis ), have high habitat suitability across Alaska no matter what threshold approach is taken. Some environmental predictors were more important than others. Specifically, the most important predictor variable, ‘frost free days,’ was critical for 15 out of 28 species as expected due to harsh winter conditions in Arctic and Subarctic regions. The second most important predictor was ‘subbasin land surface runoff’, a variable that indicates the amount of discharge and runoff, while the third most important predictor was ‘snow cover’ another indication of winter conditions. Overall, the ability to understand the effect of future climate scenarios on the establishment of AIS was challenging. A detailed dataset of freshwater temperatures and water chemistry (e.g., pH, calcium) would greatly improve the ability to predict invasiveness of freshwater species to Alaska’s ecosystems on a regional basis. Future studies may benefit from a more focused geographic scope examining a group of subbasins or a regional basin rather than the entire state. These drainages could be selected based upon the mostly likely locations of introduction pathways. The two most prevalent pathway risks for AIS are in-state transfer and stowaways/contaminants. Although there are examples of introductions from other pathways, the risk is somewhat mitigated by Alaska’s climate and regulations. However, variable application of protocols for inspection and cleaning of fishing gear, watercraft, and other similar items while traveling into Alaska as well as transferring from waterbody to waterbody within the state creates a substantial risk in introducing invasive species. We plot cumulative invasive vulnerability for all subbasins and for the top 10% of subbasins (Appendix 3).
Alaska↗
The United States National Climate Assessment - Alaska Technical Regional Report
The Alaskan landscape is changing, both in terms of effects of human activities as a consequence of increased population, social and economic development and their effects on the local and broad landscape; and those effects that accompany naturally occurring hazards such as volcanic eruptions, earthquakes, and tsunamis. Some of the most prevalent changes, however, are those resulting from a changing climate, with both near term and potential upcoming effects expected to continue into the future. Alaska's average annual statewide temperatures have increased by nearly 4°F from 1949 to 2005, with significant spatial variability due to the large latitudinal and longitudinal expanse of the State. Increases in mean annual temperature have been greatest in the interior region, and smallest in the State's southwest coastal regions. In general, however, trends point toward increases in both minimum temperatures, and in fewer extreme cold days. Trends in precipitation are somewhat similar to those in temperature, but with more variability. On the whole, Alaska saw a 10-percent increase in precipitation from 1949 to 2005, with the greatest increases recorded in winter. The National Climate Assessment has designated two well-established scenarios developed by the Intergovernmental Panel on Climate Change (Nakicenovic and others, 2001) as a minimum set that technical and author teams considered as context in preparing portions of this assessment. These two scenarios are referred to as the Special Report on Emissions Scenarios A2 and B1 scenarios, which assume either a continuation of recent trends in fossil fuel use (A2) or a vigorous global effort to reduce fossil fuel use (B1). Temperature increases from 4 to 22°F are predicted (to 2070-2099) depending on which emissions scenario (A2 or B1) is used with the least warming in southeast Alaska and the greatest in the northwest. Concomitant with temperature changes, by the end of the 21st century the growing season is expected to lengthen by 15-25 days in some areas of Alaska, with much of that corresponding with earlier spring snow melt. Future projections of precipitation (30-80 years) over Alaska show an increase across the State, with the largest changes in the northwest and smallest in the southeast. Because of increasing temperatures and growing season length, however, increased precipitation may not correspond with increased water availability, due to temperature related increased evapotranspiration. The extent of snow cover in the Northern Hemisphere has decreased by about 10 percent since the late 1960s, with stronger trends noted since the late 1980s. Alaska has experienced similar trends, with a strong decrease in snow cover extent occurring in May. When averaged across the State, the disappearance of snow in the spring has occurred from 4 to 6 days earlier per decade, and snow return in fall has occurred approximately 2 days later per decade. This change appears to be driven by climate warming rather than a decrease in winter precipitation, with average winter temperatures also increasing by about 2.5°F. The extent of sea ice has been declining, as has been widely published in both national and scientific media outlets, and is projected to continue to decline during this century. The observed decline in annual sea ice minimum extent (September) has occurred more rapidly than was predicted by climate models and has been accompanied by decreases in ice thickness and in the presence of multi-year ice. This decrease was first documented by satellite imagery in the late 1970s for the Bering and Chukchi Seas, and is projected to continue, with the potential for the disappearance of summer sea ice by mid- to late century. A new phenomenon that was not reported in previous assessments is ocean acidification. Uptake of carbon dioxide (CO2) by oceans has a significant effect on marine biogeochemistry by reducing seawater pH. Ocean acidification is of particular concern in Alaska, because cold sea water absorbs CO2 more rapidly than warm water, and a decrease in sea ice extent has allowed increased sea surface exposure and more uptake of CO2 into these northern waters. Ocean acidification will likely affect the ability of organisms to produce and maintain shell material, such as aragonite or calcite (calcium carbonate minerals structured from carbonate ions), required by many shelled organism, from mollusks to corals to microscopic organisms at the base of the food chain. Direct biological effects in Alaska further along the food chain have yet to be studied and may vary among organisms. Some of the potentially most significant changes to Alaska that could result from a changing climate are the effects on the terrestrial cryosphere - particularly glaciers and permafrost. Alaskan glaciers are changing at a rapid rate, the primary driver appearing to be temperature. Statewide, glaciers lost 13 cubic miles of ice annually from the 1950s to the 1990s, and that rate doubled in the 2000s. However, like temperature and precipitation, glacier ice loss is not spatially uniform; most glaciers are losing mass, yet some are growing (for example Hubbard Glacier in southeast Alaska). Alaska glaciers with the most rapid loss are those terminating in sea water or lakes. With this increasing rate of melt, the contribution of surplus fresh water entering into the oceans from Alaska's glaciers, as well as those in neighboring British Columbia, Canada, is approximately 20 percent of that contributed by the Greenland Ice Sheet. Permafrost degradation (that is, the thawing of ice-rich soils) is currently (2012) impacting infrastructure and surface-water availability in areas of both discontinuous and continuous ground ice. Over most of the State, the permafrost is warming, with increasing temperatures broadly consistent with increasing air temperatures. On the Arctic coastal plain of Alaska, permafrost temperatures showed some cooling in the 1950s and 1960s but have been followed by a roughly 5°F increase since the 1980s. Many areas in the continuous permafrost zone have seen increases in temperature in the seasonally active layer and a decrease in re-freezing rates. Changes in the discontinuous permafrost zone are initially much more observable due to the resulting thermokarst terrain (land surface formed as ice rich permafrost thaws), most notable in boreal forested areas. Climate warming in Alaska has potentially broad implications for human health and food security, especially in rural areas, as well as increased risk for injury with changing winter ice conditions. Additionally, such warming poses the potential for increasing damage to existing water and sanitation facilities and challenges for development of new facilities, especially in areas underlain by permafrost. Non-infectious and infectious diseases also are becoming an increasing concern. For example, from 1999 to 2006 there was a statistically significant increase in medical claims for insectbite reactions in five of six regions of Alaska, with the largest percentage increase occurring in the most northern areas. The availability and quality of subsistence foods, normally considered to be very healthy, may change due to changing access, changing habitats, and spoilage of meat in food storage cellars. These and other trends and potential outcomes resulting from a changing climate are further described in this report. In addition, we describe new science leadership activities that have been initiated to address and provide guidance toward conducting research aimed at making available information for policy makers and land management agencies to better understand, address, and plan for changes to the local and regional environment. This report cites data in both metric and standard units due to the contributions by numerous authors and the direct reference of their data.
Alaska↗
Geologic studies in Alaska by the U.S. Geological Survey, 1999
The collection of nine papers that follow continue the series of U.S. Geological Survey (USGS) investigative reports in Alaska under the broad umbrella of the geologic sciences. The series presents new and sometimes preliminary findings that are of interest to earth scientists in academia, government, and industry; to land and resource managers; and to the general public. Reports presented in Geologic Studies in Alaska cover a broad spectrum of topics from various parts of the State (fig. 1), serving to emphasize the diversity of USGS efforts to meet the Nation's needs for earth-science information in Alaska. The papers in this volume are organized under the topics: Hazards, Geologic Framework, Environment and Climate, and Resources. This organization is intended to reflect the scope and objectives of USGS geologic programs currently active in Alaska. The two Hazards studies discuss volcano-related topics in the seismically active southcentral Alaska region. The first paper revisits the eruptive events of Redoubt Volcano that occurred more than a decade ago and the subsequent development of the Alaska Volcano Observatory (AVO). This treatise documents the historic impact of this eruption and briefly summarizes the state of our knowledge of the other Cook Inlet, Alaska Peninsula, and Aleutian Island volcanoes. Finally, it discusses the recent role that AVO has had in seismic station installation and hazard assessment at volcanically active sites throughout the world. The second paper discusses the eruptive history of Snowy Mountain in the upper Alaska Peninsula. Because subsets of its 25-30 lava flows erupted as packages in short episodes, calculation of the volcano's lifetime average volumetric eruption rate is problematic. A portion of the cone was hydrothermally weakened and collapsed in the late Holocene producing a 22-km2 debris avalanche. Geologic Framework studies provide background information that is the scientific basis for present and future earth science investigations. The first paper compares and contrasts the Insular-Intermontane suture zone (IISZ) of southeast Alaska with the Adria-Europe suture zone (AESZ) of Switzerland and Hungary. The study develops the hypothesis that the zones have distinct differences as well as similarities and neither is a simple lithotectonic terrane boundary. The second paper discusses the relation among volcanic, glacial, and tectonic activity in the Cold Bay and False Pass 1 :250,000-scale quadrangles on the Alaska Peninsula. During Pleistocene time, continental-shelf glaciations and two massive volcanic centers were the dominant controls over landscape development. The third paper gives detailed geologic information for Paleozoic rocks within the Taylor Mountains D-1 quadrangle portion of the Holitna Lowland of southwestern Alaska. Because of the excellent preservation of megafossils, these Silurian and Ordovician strata lend themselves to detailed statigraphic investigations. Further, low thermal alteration indices of this area have made them a potential target of petroleum exploration. The final report in this section discusses the development of a new spectral enhancement approach for interpreting Multispectral Scanner (MSS) and Thematic Mapper (TM) satellite images. This technique enhances the use of remote sensing data in identifying geologic units in areas that have been poorly investigated. This study used this technique to better define the distribution of a JMtu (mafic, ultramafic, and sedimentary) unit and a PzZrqs (pelitic and quartzitic schist) unit. Environment and climate studies are the emphasis of two papers. One presents the first radiocarbon-dated postglacial vegetation history of the Kenai Mountains of southcentral Alaska. This reconstruction is the result of the analysis of pollen assemblages and peat from sediments collected in Tern Lake and presents a minimum age for deglaciation of these interior valleys at 9,31 0±200 yr B .P. Current vegetation, however, developed within the past ca. 2,500 years. A second study discusses the cycling of arsenic and cadmium in sub-arctic boreal forest ecosystems typical of interior Alaska and defines the importance of various natural (geogenic) sources. The transport and uptake into vegetation of these elements from soils developed from loess as well as soils developed from the major rock units is presented. The bioaccumulation of cadmium in willow (Salix sp.) and its potential consequence to the health of browsing animals is discussed. Papers related to resource issues comprise the topic of the final report. This paper presents a brief statistical summary of the geochemistry of rock samples collected in the east-central portion of the Eagle 1 :250,000-scale quadrangle. This study helps define the rock unit source of both resource- and environmental-based chemical elements of interest in the Fortymile mining district. Two bibliographies at the end of the volume list reports covering Alaska earth science topics in USGS publications during 1999 and reports about Alaska by USGS authors in non-USGS publications during the same period.
Alaska↗
Glaciers of North America - Glaciers of Alaska
Glaciers cover about 75,000 km 2 of Alaska, about 5 percent of the State. The glaciers are situated on 11 mountain ranges, 1 large island, an island chain, and 1 archipelago and range in elevation from more than 6,000 m to below sea level. Alaska's glaciers extend geographically from the far southeast at lat 55 deg 19'N., long 130 deg 05'W., about 100 kilometers east of Ketchikan, to the far southwest at Kiska Island at lat 52 deg 05'N., long 177 deg 35'E., in the Aleutian Islands, and as far north as lat 69 deg 20'N., long 143 deg 45'W., in the Brooks Range. During the 'Little Ice Age', Alaska's glaciers expanded significantly. The total area and volume of glaciers in Alaska continue to decrease, as they have been doing since the 18th century. Of the 153 1:250,000-scale topographic maps that cover the State of Alaska, 63 sheets show glaciers. Although the number of extant glaciers has never been systematically counted and is thus unknown, the total probably is greater than 100,000. Only about 600 glaciers (about 1 percent) have been officially named by the U.S. Board on Geographic Names (BGN). There are about 60 active and former tidewater glaciers in Alaska. Within the glacierized mountain ranges of southeastern Alaska and western Canada, 205 glaciers (75 percent in Alaska) have a history of surging. In the same region, at least 53 present and 7 former large ice-dammed lakes have produced jokulhlaups (glacier-outburst floods). Ice-capped volcanoes on mainland Alaska and in the Aleutian Islands have a potential for jokulhlaups caused by subglacier volcanic and geothermal activity. Because of the size of the area covered by glaciers and the lack of large-scale maps of the glacierized areas, satellite imagery and other satellite remote-sensing data are the only practical means of monitoring regional changes in the area and volume of Alaska's glaciers in response to short- and long-term changes in the maritime and continental climates of the State. A review of the literature for each of the 11 mountain ranges, the large island, the island chain, and the archipelago was conducted to determine both the individual and the regional status of Alaskan glaciers and to characterize changes in thickness and terminus position of representative glaciers in each mountain range or island group. In many areas, observations used for determining changes date from the late 18th or early 19th century. Temperature records at all Alaskan meteorological recording stations document a 20th century warming trend. Therefore, characterizing the response of Alaska's glaciers to changing climate helps to quantify potential sea-level rise from past, present, and future melting of glacier ice (deglaciation of the 14 glacierized regions of Alaska), understand present and future hydrological changes, and define impacts on ecosystems that are responding to deglacierization. Many different types of data were scrutinized to determine baselines and to assess the magnitude of glacier change. These data include the following: published descriptions of glaciers (1794-2000), especially the comprehensive research by Field (1975a) and his colleagues in the Alaska part of Mountain Glaciers of the Northern Hemisphere, aerial photography (since 1926), ground photography (since 1884), airborne radar (1981-91), satellite radar (1978-98), space photography (1984-94), multispectral satellite imagery (since 1972), aerial reconnaissance and field observations made by many scientists during the past several decades, and various types of proxy data. The published and unpublished data available for each glacierized region and individual glacier varied significantly. Geospatial analysis of digitized U.S. Geological Survey (USGS) topographic maps is used to statistically define selected glaciological parameters in the eastern part of the Alaska Range. The analysis determined that every mountain range and island group investigated can be characterized by significant glacier retreat, thinning, and (or) stagnation, especially those glaciers that end at lower elevations. At some locations, glaciers completely disappeared during the 20th century. In other areas, retreat that started as early as the early 18th century has continued into the 21st century. Ironically, in several areas, retreat is resulting in an increase in the total number of glaciers; even though individual glaciers are separating, the volume and area of ice continue to decrease.
Alaska↗
Wandering terranes in southern Alaska: The Aleutia Microplate and implications for the Bering Sea
Paleomagnetic and geological data suggest that much of southern Alaska is a collage of tectonostratigraphic terranes which originated in Mesozoic time at paleolatitudes far south of their present position. The time of ‘docking’ of the terranes against cratonic Alaska is critical to defining their amalgamated size and extent during their northward motion as well as their role in the evolution of the Bering Sea. One of the largest of the tectonostratigraphic terranes, the Peninsular terrane of south central and southwestern Alaska, extends offshore along the outer Bering Sea continental margin (Beringia). Paleomagnetic data suggest that this terrane has moved northward through all of Cenozoic time, but geologic data imply that the terrane had accreted to Alaska by the end of the Mesozoic. In early Cenozoic time the eastern part of the Aleutian arc appears to have been superimposed on the Peninsular terrane, and postulated northward Cenozoic motion of the terrane would therefore have required northward motion of the arc. Two accretion models, based on docking times for terranes in Alaska, are proposed, and they illustrate that large areas of the abyssal Bering Sea, the Alaska Peninsula, the Aleutian arc, and the Beringian continental margin may be part of a superterrane or microplate called Aleutia (microplate as defined by Beck et al. (1980), i.e., a microplate is a displaced segment of lithosphere that has crustal roots, whereas a superterrane is an amalgamation of terranes which may or may not be rootless). Model A implies that the Aleutian arc developed in situ on the southern edge of Aleutia after the microplate had docked. In model B, the final docking time of the Peninsular terrane is late Cenozoic, which implies that the Aleutia microplate encompasses a mammoth area that includes parts of southern Alaska, the Alaska Peninsula, the southern Beringian margin, the abyssal Bering Sea (Kula plate), and the Aleutian arc. If model A is correct, the docking time of the Peninsular terrane is late Mesozoic or earliest Tertiary. The Aleutia microplate in this model is made up solely of the abyssal Bering Sea (Kula plate), which presumably docked at the same time or slightly after the Peninsular terrane accreted against Alaska. If model B is correct, that is, if the Aleutia collided with nuclear Alaska during the Cenozoic, then a late Cenozoic suture zone, the vestige of a large open sea that must have closed between Aleutia and Alaska, must exist in south central and southwest Alaska. Either evidence for Cenozoic closure and suturing has been obliterated in Alaska or the inferences of Cenozoic terrane motion derived from paleomagnetic data are suspect.
Alaska↗
Alaska Landbird Conservation Plan
Alaska is a land of extremes. The diversity of its avifauna reflects the heterogeneity of its landscape, with more than 500 species of birds recorded in the state. Species inhabiting primarily terrestrial habitats, known collectively as landbirds, constitute the largest and most ecologically diverse component of the Alaska avifauna. Habitats used by landbirds range from temperate rainforests in southeastern Alaska to Arctic tundra across much of northern Alaska. Most of these landbird species are migratory, and four major global migration flyways converge on rich breeding areas in Alaska. Alaska has one endemic landbird species, the McKay’s Bunting, and is home to an impressive number of landbird populations for which it hosts a large proportion of the regional, continental, or global population. Thus, Alaska has a significant stewardship responsibility for these particular landbird species and subspecies. Habitats in Alaska remain largely pristine due to the region’s remote nature, vast size, and small human population. Alaska’s growing population and attendant economic development, however, present many challenges that could affect all wildlife, including landbirds. Threats in Alaska are often considered to be less significant than those occurring elsewhere, where habitats are being altered by more rapidly increasing anthropogenic pressures, but they carry far-reaching consequences nonetheless. Habitats and ecosystem dynamics are changing rapidly due to the magnitude of climate warming at high latitudes. As such, effective landbird conservation in Alaska requires a broad, landscape-scale approach. Conservation of landbirds over such an extensive and diverse landscape also demands that we integrate efforts in habitat management, population monitoring, research, education, and outreach at local, regional, continental, and international scales. Information on distribution and habitat requirements of landbirds should be incorporated into land-use planning decisions. Synthesizing information on distribution and population trends of landbirds is a critical, time-sensitive task. Such information should be provided in a form that is readily available to land managers and policy decision-makers. The primary objectives of this plan are to (1) describe the region and Alaska’s landbird avifauna; (2) identify species of concern, important habitats, and key information needs; (3) highlight major conservation issues and threats to landbirds; and (4) identify potential conservation actions. We first examine landbird conservation at the statewide level within broad perspectives (regional, continental, and global), then take a detailed look at the specific issues, information needs, and potential conservation actions within each Bird Conservation Region in Alaska.
Alaska↗