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At least 235 records · Page 13Linked to original sources
USGS2019

Modeling sediment bypassing around idealized rocky headlands

Alongshore sediment bypassing rocky headlands remains understudied despite the importance of characterizing littoral processes for erosion abatement, beach management, and climate change adaptation. To address this gap, a numerical model sediment transport study was developed to identify controlling factors and mechanisms for sediment headland bypassing potential. Four idealized headlands were designed to investigate sediment flux around the headlands using the process-based hydrodynamic model Delft-3D and spectral wave model SWAN. The 120 simulations explored morphologies, substrate compositions, sediment grain sizes, and physical forcings (i.e., tides, currents, and waves) commonly observed in natural settings. A generalized analytical framework based on flow disruption and sediment volume was used to refine which factors and conditions were more useful to address sediment bypassing. A bypassing parameter was developed for alongshore sediment flux between upstream and downstream cross-shore transects to determine the degree of blockage by a headland. The shape of the headland heavily influenced the fate of the sediment by changing the local angle between the shore and the incident waves, with oblique large waves generating the most flux. All headlands may allow sediment flux, although larger ones blocked sediment more effectively, promoting their ability to be littoral cell boundaries. The controlling factors on sediment bypassing were determined to be wave angle, size, and shape of the headland, and sediment grain size.

Journal of Marine Science and Engineering↗
USGS2016

Observations of nearshore groundwater discharge: Kahekili Beach Park submarine springs, Maui, Hawaii

Study region The study region encompasses the nearshore, coastal waters off west Maui, Hawaii. Here abundant groundwater—that carries with it a strong land-based fingerprint—discharges into the coastal waters and over a coral reef. Study focus Coastal groundwater discharge is a ubiquitous hydrologic feature that has been shown to impact nearshore ecosystems and material budgets. A unique combined geochemical tracer and oceanographic time-series study addressed rates and oceanic forcings of submarine groundwater discharge at a submarine spring site off west Maui, Hawaii. New hydrological insights for the region Estimates of submarine groundwater discharge were derived for a primary vent site and surrounding coastal waters off west Maui, Hawaii using an excess 222 Rn ( t 1/2 = 3.8 d) mass balance model. Such estimates were complemented with a novel thoron ( 220 Rn, t 1/2 = 56 s) groundwater discharge tracer application, as well as oceanographic time series and thermal infrared imagery analyses. In combination, this suite of techniques provides new insight into the connectivity of the coastal aquifer with the near-shore ocean and examines the physical drivers of submarine groundwater discharge. Lastly, submarine groundwater discharge derived constituent concentrations were tabulated and compared to surrounding seawater concentrations. Such work has implications for the management of coastal aquifers and downstream nearshore ecosystems that respond to sustained constituent loadings via this submarine route.

Hawaii↗
USGS1975

Preliminary report on the reconnaissance engineering geology of the Yakutat area, Alaska, with emphasis on evaluation of earthquake and other geologic hazards

Yakutat, situated about 225 miles northwest of Juneau, Alaska, near the shores of the Gulf of Alaska, has a setting that calls for superlatives. Within the Yakutat region are some of the tallest mountains, some of the heaviest snowfalls, and the largest glacier in North America. Between the abrupt mountain front and the Gulf of Alaska lies a very gently sloping plain of outwash derived from repeated cycles of advance followed by melt and retreat of glaciers during the Quaternary Period. The latest melting probably took place 500 to 600 years ago. Yakutat is built upon the moderately steep moraine that is the product of melting of one of these glaciers. Near Yakutat, surficial deposits are as much as 700 feet thick and probably overlie siltstone, sandstone, and mudstone. The eight general categories of mapped surficial deposits include artificial fill, organic, eolian, beach, delta-estuarine, alluvial, and outwash deposits, and deposits of the outer Yakutat Bay moraine complex.

Alaska↗
USGS1949

Coal investigations on the southern margin of the Homer district, Kenai coal field, Alaska, in 1947-48

The presence of coal in the Tertiary Kenai formation of western Kenai Peninsula has been known since 1880, chiefly as exposed along the north shore of Kachemak Bay and the adjoining east shore of Cook Inlet (fig. 1). Several early attempts were made to develop a commercial mine in this area in the period 1888-1902 but none progressed beyond the prospecting stage and little coal was produced. In 1915 the mining of coal-was started at the Bluff Point mine, 1 1/2 miles west of Homer. Available records indicate that this mine produced between 20,000 and 25,000 tons of coal before closing in 1324. No further attempt at mining was made until 1946, when the Homer Coal Corporation began development near the site of the old Bluff Point mine. Development work during 1946 and 1947 included construction of a truck-loading bunker, mess hail, bunkhouse, and an incline end hoist for raising coal from the tunnel in the face of the beach bluff. Only a small amount of underground work was done in 1946 and 1947, and practically none in 1948. A preliminary step toward more extended investigation of the coal deposits of the Homer district was made by the writer, accompanied by T. J. Jolley of the U. S. Bureau of Mines, in the summer of 1946. Several days were spent in examining the principal coal exposures near Homer and collecting samples to determine the desirability of more detailed investigation. Detailed examination of the coal deposits of the Homer district was started by the Geological Survey in 1947. The period July 17 to September 14 was spent by the writer, assisted by H. C. Wagner, geologist, and L. A. Hale, field assistant, in reconnaissance of isolated coal exposures in an area extending several miles north of Homer, and in measuring detailed stratigraphic sections in the bluffs just north of Homer between Coal (Bidarki) and Fritz Creeks.

Alaska↗
USGS1982

Pacific summary report 2: A revision of Outer Continental Shelf oil and gas activities in the Pacific (Southern California) and their onshore impacts: A summary report, May 1980

The Pacific Outer Continental Shelf (OCS) is an established hydrocarbon-producing region. Oil and gas have been produced from the Santa Barbara Channel (both State and Federal acreage) since 1896. Almost 77,000 barrels of oil are produced from the California Federal OCS each day as of December 1981, and leases on State tidelands produce about 40,000 barrels of oil per day. This highly developed area is, of course, but a small part of the Pacific OCS, which also includes Northern California, Washington, and Oregon. The petroleum industry has expressed interest in exploring frontier areas, and as frontier acreage is offered in future lease sales, exploration, development, and production may move out into deeper water. The technology is currently being developed and tested to allow deepwater exploration. To date, offshore drilling operations have resulted in the delineation of 11 offshore oil and gas fields and 2 gas fields in the Southern California OCS. A recent discovery off Point Arguello, California, may lead to delineation of a new field. Reserve estimates have been made for the known fields in the region. Remaining recoverable reserves are estimated at 787 million barrels of oil and over 1.7 trillion cubic feet of gas as of December 31, 1980. Estimates of undiscovered recoverable resources in the offshore Santa Maria Basin and Southern California OCS are over 3.5 billion barrels of oil and in excess of 5 trillion cubic feet of gas. To date, there have been seven oil and gas lease sales in the Pacific OCS Region. An average of one lease sale per year is scheduled through 1985. Industry interest indicates that the Santa Barbara Channel's potential has not yet been fully explored, and some basins to the south, as well as in the Santa Maria Basin, are now gaining considerable interest. Future exploratory activity in the San Pedro Bay and the Santa Maria Basin is likely to increase. Exploration, development, and production in the Pacific OCS Region are increasing at a moderate pace. Pipelines continue to be the preferred mode of transporting Pacific OCS hydrocarbons to shore. The State and the Federal Governments have expressed a commitment to the use of pipelines where possible and economically feasible. Tankers traveling in the Pacific and entering California ports carry, for the most part, imported oil. The region is active in OCS transportation planning; the Bureau of Land Management works through the Pacific States Regional Technical Working Group Committee. Onshore, the Petroleum Transportation Committee (formerly the Joint Government/Industry Pipeline Working Group) is evaluating a number of transportation scenarios. The nearshore and onshore petroleum processing facilities in the Pacific Region service onshore and offshore oil and gas exploration, development, and production, as well as the international oil market. Many of the onshore facilities have been in operation for years, supporting California's extensive onshore and offshore production. Several new facilities have been proposed, are currently under construction, or have recently opened. Shell Oil opened a crude oil distribution facility near Long Beach in December 1980. Operations began at Union Oil's Mandalay Beach separation and treatment plant in December 1981. The Pacific Offshore Pipeline Company, a subsidiary of the Pacific Lighting Corporation, is planning to build a gas treatment plant at Las Flores Canyon; completion of this project is scheduled for July 1983. It is expected that these new facilities, in addition to the established plants, will be able to accommodate any new OCS production in the near term from previously leased areas.

California↗
USGS1952

Coal investigations in the Homer district, Kenai coal field, Alaska, in 1950 and 1951

This report presents the results of work done in the last three weeks of the 1950 field season and in all of the 1951 season, and supplements reports by Barnes (19149) and Cobb (1950, 1951). Barnes' report covers investigations of coal-bearing rocks of the Tertiary Kenai formation in a coastal belt between Bluff Point and the head of Kachemak Bay (pl. 2). Cobb's reports deal with similar rocks exposed along the coast between Bluff Point and the beach bluffs about 7 miles south of the village of Cohoe, and in the lower reaches of the Ninilchik River valley. The present report covers extensions of previous mapping in the valleys of Deep Creek and the Anchor River, and on high land between the area covered by Barnes' report and the Anchor River valley. The results of ground and aerial reconnaissance of most of the Homer district also are presented. The writer, assisted by F. J. Markewioz, carried on the field work which is the basis for this report, between August 13 mad September 6, 1950, and between May 10 and August 30, 1951. Field work included traverses along Deep Creek and the Anchor River, and between the southeast end of Tustumena Lake and the head of Kachemak Bay. It included also the detailed measurement and tracing of coal beds on the upland north and northwest of Homer, sampling of coal beds along the northwest shore of Kachemak Bay and the southeast shore of Cook Inlet, and both ground and aerial reconnaissance of the rest of the Homer district and adjoining areas. The writer is indebted to James W. Scott, Forester, U. S. Bureau of Land Management, Lomer, Alaska, who accompanied him on a traverse from Tustumena Lake to Kaohemak Bay and assisted at many other times during the 1950 and 1951 field seasons. Ralph Gaetano and Thomas Shelford of Homer were of great assistance in locating and reaching isolated outcrops of coal-bearing rooks. Daniel B. Krinsley, of the Alaska Terrain and Permafrost Section of the U. S. Geological Survey, has generously made available the results of many of his observations in remote parts of the Homer district which could not be visited by the writer.

Alaska↗
USGS1966

Geologic effects of the March 1964 earthquake and associated seismic sea waves on Kodiak and nearby islands, Alaska

Kodiak Island and the nearby islands constitute a mountainous landmass with an aggregate area of 4,900 square miles that lies at the western border of the Gulf of Alaska and from 20 to 40 miles off the Alaskan mainland. Igneous and metamorphic rocks underlie most of the area except for a narrow belt of moderately to poorly indurated rocks bordering the Gulf of Alaska coast and local accumulations of unconsolidated alluvial and marine deposits along the streams and coast. The area is relatively undeveloped and is sparsely inhabited. About 4,800 of the 5,700 permanent residents in the area live in the city of Kodiak or at the Kodiak Naval Station. The great earthquake, which occurred on March 27, 1964, at 5:36 p.m. Alaska standard time (March 28,1964, 0336 Greenwich mean time), and had a Richter magnitude of 8.4-8.5, was the most severe earthquake felt on Kodiak Island and its nearby islands in modern times. Although the epicenter lies in Prince William Sound 250 miles northeast of Kodiak—the principal city of the area—the areal distribution of the thousands of aftershocks that followed it, the local tectonic deformation, and the estimated source area of the subsequent seismic sea wave, all suggest that the Kodiak group of islands lay immediately adjacent to, and northwest of, the focal region from which the elastic seismic energy was radiated. The duration of strong ground motion in the area was estimated at 2½ minutes. Locally, the tremors were preceded by sounds audible to the human ear and were reportedly accompanied in several places by visible ground waves. Intensity and felt duration of the shocks during the main earthquake and aftershock sequence varied markedly within the area and were strongly influenced by the local geologic environment. Estimated Mercalli intensities in most areas underlain by unconsolidated Quaternary deposits ranged from VIII to as high as IX. In contrast, intensities in areas of upper Tertiary rock ranged from VII to VIII, and in areas of relatively well indurated lower Tertiary and Mesozoic rocks, from VI to VII. Local subsidence of as much as 10 feet was widespread in noncohesive granular deposits through compaction, flow, and sliding that resulted from vibratory loading during the earthquake. This phenomenon, which was largely restricted to saturated beach and alluvial deposits or artificial fill, was locally accompanied by extensive cracking of the ground and attendant ejection of water and water-sediment mixtures. Numerous landslides, including a wide variety of rockfalls, rockslides, and flows along steep slopes, were triggered by the long-duration horizontal and vertical accelerations during the earthquake. The landslides are most numerous in a narrow belt along the southeast coast of Kodiak Island and the nearby offshore islands. Their abundance appears to be related to an area underlain predominantly by Tertiary rocks. Temporary and permanent changes of level occurred after the earthquake in some wells, lakes, and streams throughout the area; ice was cracked, and the salinity of a few wells increased. Permanent change of water level at some localities appears to be related to readjustments of fracture porosity by earthquake-induced movements of bedrock blocks. Increased salinity of wells in coastal areas resulted from encroachment of seawater into aquifiers after subsidence during the earthquake, and to flooding of watersheds by seismic sea waves. Vertical displacements, both downward and upward, occurred throughout the area as a result of crustal warping along a northeast-trending axis. Most of Kodiak and all of Afognak, Shuyak, and adjacent islands are within a regional zone of subsidence whose trough plunges gently northeastward and approximately coincides with the mountainous backbone of Kodiak Island. Subsidence in excess of 6 feet occurred throughout the northern part of the zone-a maximum subsidence of 6½ feet having occurred on Marmot and, eastern Afognak Islands. Southeast of the axis of tectonic tilting, uplift of at least 2lh feet occurred in a narrow zone that includes most of the southeasterly capes of Kodiak Island, the southeastern half of Sitkalidak Island, and Sitkinak Island. The uplift is inferred to extend offshore over much or all of the continental shelf adjacent to the Kodiak group of islands. Within the affected area, tectonic subsidence, which was locally augmented by surficial subsidence of unconsolidated. deposits, caused widespread inundation of shorelines and attendant damage to intertidal organisms, nearshore terrestrial vegetation, and salmon-spawning areas. The most devastating effect of the earthquake on Kodiak Island and nearby islands resulted from seismic sea waves that probably originated along a linear zone of differential uplift in the Gulf of Alaska. A train of at least seven seismic sea waves, having initial periods of 50–55 minutes, struck along all the southeast coast of the island group from 38 to 63 minutes after the earthquake. The southeast shores were repeatedly washed by destructive waves having runup heights along exposed coasts of perhaps as much as 40 feet above existing tide level, and of 8–20 feet along protected shores. Runup heights of the waves were much less on the northwest and southwest sides of the islands, and no wave damage was incurred there. Locally, high-velocity currents that accompanied the waves caused intense erosion and redistribution of unconsolidated natural and artificial shore deposits and of shallow sea-floor deposits. The Alaska earthquake was the greatest natural catastrophe to befall the Kodiak Island area in historic time. The combination of seismic shock and the earthquake-related tectonic deformation and seismic sea waves took 18 lives, destroyed property worth about $45 million, and resulted in estimated losses of income to the fishing industry of an additional $5 million. Most of the damage and all of the loss of life were directly attributable to the seismic sea waves that crippled the city of Kodiak, wiped out the village of Kaguyak, and destroyed most of the village of Old Harbor and parts of the villages of Afognak and Uzinki. Bridges and segments of the highways in the vicinity of the city of Kodiak were washed out, and parts of the Kodiak Naval Station were inundated and damaged. Especially serious to all the damaged communities was the loss of fishing boats, seafood processing plants, and other waterfront installations, which had been the mainstay of the economy. Additional heavy losses resulted from the combined regional tectonic and local surficial subsidence that occurred during the earthquake. Widespread shoreline flooding by high tides necessitated raising, protecting, or removing many installations otherwise undamaged by the earthquake or waves. Structural damage attributable to seismic shock during the earthquake was relatively light and was restricted to areas underlain by saturated unconsolidated deposits. The chief structural failure in the area as a result of shaking was the collapse of part of a cannery built on saturated beach deposits that were partially liquefied during the earthquake. Minor structural damage resulted from differential settlement and cracking of the ground on natural granular deposits and artificial fills. The overwhelming majority of structures are constructed on indurated bedrock; none of these sustained damage other than small losses resulting from shifting about and breakage of their contents.

Alaska↗
USGS2016

Modeling and simulation of storm surge on Staten Island to understand inundation mitigation strategies

Hurricane Sandy made landfall on October 29, 2012, near Brigantine, New Jersey, and had a transformative impact on Staten Island and the New York Metropolitan area. Of the 43 New York City fatalities, 23 occurred on Staten Island. The borough, with a population of approximately 500,000, experienced some of the most devastating impacts of the storm. Since Hurricane Sandy, protective dunes have been constructed on the southeast shore of Staten Island. ADCIRC+SWAN model simulations run on The City University of New York's Cray XE6M, housed at the College of Staten Island, using updated topographic data show that the coast of Staten Island is still susceptible to tidal surge similar to those generated by Hurricane Sandy. Sandy hindcast simulations of storm surges focusing on Staten Island are in good agreement with observed storm tide measurements. Model results calculated from fine-scaled and coarse-scaled computational grids demonstrate that finer grids better resolve small differences in the topography of critical hydraulic control structures, which affect storm surge inundation levels. The storm surge simulations, based on post-storm topography obtained from high-resolution lidar, provide much-needed information to understand Staten Island's changing vulnerability to storm surge inundation. The results of fine-scale storm surge simulations can be used to inform efforts to improve resiliency to future storms. For example, protective barriers contain planned gaps in the dunes to provide for beach access that may inadvertently increase the vulnerability of the area.

New York↗
USGS1994

Carbonate deposition, Pyramid Lake subbasin, Nevada: 1. Sequence of formation and elevational distribution of carbonate deposits (Tufas)

During the late Quaternary, the elevation of terrace cutting and carbonate deposition in the Pyramid Lake subbasin were controlled by constancy of lake level imposed by spill to adjoining subbasins. Sill elevations are 1177-1183 m (Mud Lake Slough Sill), 1207 m (Emerson Pass Sill), and 1265 m (Darwin Pass Sill). Carbonate deposition was favored by: (1) hydrologic closure, (2) proximity to a source of calcium, (3) elevated water temperature, and (4) a solid substrate. The thickness and aspect of tufa are a function of lake-level dynamics. Relatively thin sheets and pendant sheets were deposited during a rising or falling lake. The upper parts of thick reef-form tufas have a horizontal aspect and were deposited in a lake which was stabilized by spill to the Carson Desert subbasin. The lower parts of the reef-form tufas are thinner and their outer surface has a vertical aspect, indicating that the lower part formed in a receding lake. The thickest and most complete sequences of tufa are mounds that border the Pyramid Lake shore. The tops of the tallest mounds reach the elevation of the Darwin Pass Sill and many mounds have been eroded to the elevations of the Mud Lake Slough Sill of the Emerson Pass Sill. The sequence of tufa formation (from oldest to youngest) displayed in these mounds is: (1) a beachrock containing carbonate-cemented volcanic cobbles, (2) broken and eroded old spheroids that contain thinolitic tufa and an outer rind of dense laminated tufa, (3) large cylindrical (tubular) tufas capped by (4) coatings of old dense tufas, and (5) several generations of old branching tufa commonly associated with thin, platy tufas and coatings of thinolitic tufa, (6) young spheroids that contain poorly oriented young thinolitic tufa in the center and several generations of radially oriented young thinolitic tufas near the outer edge, (7) a transitional thinolite-to-branching tufa, (8) two or more layers of young branching tufa, (9) a 0.5-cm-thick layer of fine-grained dolomite, (10) a 2-cm-thick layer of young dense laminated tufa, (11) a 0.1-cm-thick layer of encrusting tufa that was covered by a beach deposit and (12) a 1.0-cm-thick layer of porous encrusting tufa that coated the beach deposit and the sides of tufa mounds. The elevational ranges of the principal varieties of tufa are not related to terrace or spill elevations. It seems likely that the distribution of tufa varieties is related to variation in the thermal structure or chemistry of Lake Lahontan. It is hypothesized that the thinolitic tufa (ikaite) formed in the near freezing hypolimnion and the braching tufa (calcite) formed in the seasonally warmer epiliminion of the lake.

Nevada↗
USGS2018

August 2008 eruption of Kasatochi volcano, Aleutian Islands, Alaska-resetting an Island Landscape

Kasatochi Island, the subaerial portion of a small volcano in the western Aleutian volcanic arc, erupted on 7-8 August 2008. Pyroclastic flows and surges swept the island repeatedly and buried most of it and the near-shore zone in decimeters to tens of meters of deposits. Several key seabird rookeries in taluses were rendered useless. The eruption lasted for about 24 hours and included two initial explosive pulses and pauses over a 6-hr period that produced ash-poor eruption clouds, a 10-hr period of continuous ash-rich emissions initiated by an explosive pulse and punctuated by two others, and a final 8-hr period of waning ash emissions. The deposits of the eruption include a basal muddy tephra that probably reflects initial eruptions through the shallow crater lake, a sequence of pumiceous and lithic-rich pyroclastic deposits produced by flow, surge, and fall processes during a period of energetic explosive eruption, and a fine-grained upper mantle of pyroclastic-fall and -surge deposits that probably reflects the waning eruptive stage as lake and ground water again gained access to the erupting magma. An eruption with similar impact on the island's environment had not occurred for at least several centuries. Since the 2008 eruption, the volcano has remained quiet other than emission of volcanic gases. Erosion and deposition are rapidly altering slopes and beaches. ?? 2010 Regents of the University of Colorado.

Alaska↗
USGS2009

Evidence for late Holocene relative sea-level fall from reconnaissance stratigraphical studies in an area of earthquake-subsided intertidal deposits, Isla Chiloé, southern Chile

At Río Pudeto and Quetalmahue, two estuaries along the northern shore of Isla Chiloé that subsided as much as 2 m in the great 1960 earthquake, reconnaissance stratigraphical studies reveal evidence of a regressive, nearshore marine sequence. The intertidal deposits include a peat-bearing, high-intertidal marsh sequence as thick as 1.4 m overlying shell- and foraminifera-bearing silt and clay layers presumed to represent a deeper water, low-intertidal environment. Stratigraphy indicates a relative sea-level fall since about 5000 years BP as evidenced by radiocarbon ages that constrain the peat-bearing sequences. Locally, low-intertidal silt and clay overlie high-intertidal peat layers, but such minor transgressions cannot be correlated from site to site. At Río Pudeto, the youngest foraminifera-bearing silt deposit is no younger than 1200 years BP. The youngest age of shells at Quetalmahue is about 2600 years BP. The oldest peat-bearing deposits that are not overlain by silt deposits are about 1350 years BP at Río Pudeto, and as old as 4900 years BP at Quetalmahue. At Río Pudeto, peat-bearing deposits, which are overlain by silt and clay, range in age from 760 to 5430 years BP, and at Quetalmahue from 290 to 5290 years BP. A beach terrace on the northwest coast of the Isla is estimated to have been emergent since 1150 + 130 years ago. Although some relatively abrupt transgressions may be due to sudden coseismic subsidence, data are not sufficient to document regional subsidence during individual plate-interface earthquakes. Seven earthquakes in south central Chile since 1520, especially those that occurred in 1575, 1737, and 1837, are thought to have been of a magnitude comparable to that of the 1960 earthquake. Although the sedimentological effects of the 1960 earthquake on the intertidal zone were dramatic, only limited evidence of possible historic earthquakes is found on Isla Chiloé and nearby islands; the ages and displacements of these earthquakes are indeterminable. Dead forests still mark some locations that subsided into the intertidal zone during the 1960 earthquake, particularly at Río Pudeto and southern coastal Chiloé. There is little evidence of post-1960 growth in any of these subsided areas. Tree-ring counts and tree-diameter measurements provide evidence that these trees survived the 1837 earthquake, and probably survived the 1737 earthquake, strongly suggesting that these earthquakes were of smaller magnitude than the 1960 event, or that the epicentre locations were further removed than the 1960 epicentre from Isla Chiloé, and that earthquake-induced relative sea-level changes differed from those occurring in 1960.

Isla Chiloé↗
USGS2016

California State Waters map series — Offshore of Aptos, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar bathymetric data (the undersea equivalent of satellite remote-sensing data in terrestrial mapping), acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The Offshore of Aptos map area is located on the Pacific Coast, on the north side of Monterey Bay, about 105 km southeast of San Francisco. The largest incorporated city in the map area, Capitola, and numerous unincorporated towns including Aptos, lie on uplifted marine terraces between the shoreline, and the northwest-trending Santa Cruz Mountains, part of California’s Coast Ranges. The map area includes the northernmost part of Santa Cruz Harbor, and Moss Landing Harbor is located about 10 km south of the map area. The offshore part of the map area is entirely within California’s State Waters and is also part of the Monterey Bay National Marine Sanctuary. In the southern part of the map area, the Soquel Canyon State Marine Conservation Area extends eastward from the limit of California’s State Waters across Soquel Canyon. The Offshore of Aptos map area is on the western margin of North American Plate—the only continental margin in the world delineated largely by transform faults. The San Andreas Fault Zone cuts through the Santa Cruz Mountains just 3.5 km northeast of the map area. The San Gregorio Fault Zone, another major plate-boundary structure, cuts through Monterey Canyon about 13 km southwest of the map area. Ongoing deformation associated with and between these major fault zones has uplifted the Santa Cruz Mountains and formed well-developed sets of marine terraces that characterize almost the entire coastal zone of the map area. The offshore part of the map area consists of relatively flat and shallow continental shelf which is underlain by variable amounts (0 to 30 m) of upper Quaternary shelf, estuarine, and fluvial sediments deposited as sea level fluctuated in the late Pleistocene. Along the southern edge of the map area, the shelf is incised by the head of Soquel Canyon, a northeast-trending tributary to the west-trending Monterey Canyon. During the last sea-level lowstand (the Last Glacial Maximum [LGM], about 21,000 years ago) Soquel Creek flowed through a paleochannel across the emergent shelf into the head of Soquel Canyon. This canyon was disconnected from its onshore watershed during the post-LGM sea-level rise of about 125 m; the abandoned paleochannel was subsequently filled with marine sediment. Coastal sediment in the Offshore of Aptos map area is supplied by coastal watersheds and bluff erosion. Sediment transport in this part of the Santa Cruz littoral cell is primarily from the northwest to the southeast and terminates in the submarine Monterey Canyon. Longshore drift is impeded by jetties at Santa Cruz Harbor, resulting in high beach erosion rates east of the harbor. Sediment dredged from the harbor mouth (estimated 300,000 yds 3 /yr) is currently being used to nourish beaches directly to the east. Farther downcoast, the rapidly eroding beach at Capitola was stabilized by construction of an about 75-m-long groin. This part of central California is exposed to large North Pacific swells from the northwest throughout the year. North Pacific swell heights range from 2 to 10 meters, with larger swells occurring from October to May. During El Niño-Southern Oscillation (ENSO) events, winter storms track farther south than they do in normal (non-ENSO) years, thereby impacting the map area more frequently and with waves of larger heights. Bedrock exposed in coastal cliffs is relatively erosion-resistant, and significant erosional events primarily are restricted to storm-wave activity that also erodes the overlying unconsolidated marine-terrace sediments. The Offshore of Aptos map area lies within the cold-temperate biogeographic zone that is called either the “Oregonian” province or the “northern California ecoregion.” This biogeographic province is maintained by the long-term stability of the southward-flowing California Current, the eastern limb of the North Pacific subtropical gyre that flows from southern British Columbia to Baja California. At its midpoint off central California, the California Current transports subarctic surface (0–500 m deep) waters southward, about 150 to 1,300 km from shore. Seasonal northwesterly winds that are, in part, responsible for the California Current, generate coastal upwelling. The south end of the Oregonian province is at Point Conception (about 310 km southeast of the map area), although its associated phylogeographic group of marine fauna may extend beyond to the area offshore of Los Angeles in southern California. The ocean off of central California has experienced a warming over the last 50 years that is driving an ecosystem shift away from the productive subarctic regime towards a depopulated subtropical environment. Seafloor habitats in the Offshore of Aptos map area lie within the “Shelf” Megahabitat class and include patchy rocky habitats, gravel-rich scour depressions, minor bedrock habitat, and predominantly sandy inner shelf. Sandy shelf habitats grade offshore to mud-dominated habitats on the midshelf in deeper water. Biological productivity resulting from coastal upwelling supports populations of Sooty Shearwater, Western Gull, Common Murre, Cassin’s Auklet, and many other less populous bird species. In addition, an observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. California sea lions and Pacific harbor seals are abundant in the map area. Common bottlenose dolphins are often observed very close to shore and in the surf zone. The large extent of exposed inner shelf bedrock supports large forests of “bull kelp,” which is well adapted for high-wave-energy environments. The kelp beds are the northernmost known habitat for the population of southern sea otters. Common fish species found in the kelp beds and rocky reefs include blue rockfish, black rockfish, olive rockfish, kelp rockfish, gopher rockfish, black-and-yellow rockfish, painted greenling, kelp greenling, and lingcod.

California↗
USGS2010

Modeling the effects of wave climate and sediment supply variability on large-scale shoreline change

The application of an integrated data analysis and modeling scheme reveals that decadal-scale shoreline evolution along a U.S. Pacific Northwest littoral cell is highly dependent on both sediment supply and wave climate variability. In particular, accurate estimates of (Columbia River) sediment supply and sediment feeding from the lower shoreface are critical components of balancing the barrier beach sediment budget and are therefore essential to making sensible shoreline change hindcasts and forecasts. A simple deterministic one-line shoreline change model, applied in a quasi-probabilistic manner, enables evaluation of the influence of sediment supply and wave climate variability through simulation of historical shoreline change. Through iteration, a range of realistic scenarios are developed to constrain decadal-scale shoreline change predictions. Modeled shoreline changes are significantly sensitive to directional changes in the incident waves, and therefore sensitive to the occurrence of interannual climatic fluctuations such as major El Niño events. A predicted increase in the intensity of the east Pacific wave climate (1.0 m increase in significant wave height in 20 yr) affects forecast shoreline positions only when this increase occurs during the winter storm season. However, the effect of this increase in storm power during any given year is small relative to the impact of major El Niño events. The model has significant skill in decadal-scale hindcasts suggesting that alongshore gradients in sediment transport dominate coastal change at this scale at this site. However, both data and model results suggest that net onshore feeding from the lower shoreface is responsible for approximately 20% of the decadal-scale coastal change. Field measurements and poor model skill at annual scale indicate that cross-shore processes likely dominate coastal change at shorter time scales.

Oregon, Washington↗
USGS1967

Effects of the earthquake of March 27, 1964, at Seward, Alaska

Seward, in south-central Alaska, was one of the towns most devastated by the Alaska earthquake of March 27, 1964. The greater part of Seward is built on an alluvial fan-delta near the head of Resurrection Bay on the southeast coast of the Kenai Peninsula. It is one of the few ports in south-central Alaska that is ice free all year, and the town’s economy is almost entirely dependent upon its port facilities. The Alaska earthquake of March 27, 1964, magnitude approximately 8.3–8.4, began at 6:36 p.m. Its epicenter was in the northern part of the Prince William Sound area; focal depth was 20–50 km. Strong ground motion at Seward lasted 3–4 minutes. During the shaking, a strip of land 50–400 feet wide along the Seward waterfront, together with docks and other harbor facilities, slid into Resurrection Bay as a result of large-scale submarine landsliding. Fractures ruptured the ground for'severa1 hundred feet back from the landslide scarps. Additional ground was fractured in the Forest Acres subdivision and on the alluvial floor of the Resurrection River valley; fountaining and sand boils accompanied the ground fracturing. Slide-generated wares, possibly seiche waves, and seismic sea waves crashed onto shore; ware runup was as much as 30 feet above mean lower low water and caused tremendous damage; fire from burning oil tanks added to the destruction. Damage from strong ground motion itself was comparatively minor. Tectonic subsidence of about 3.6 feet resulted in low areas being inundated at high tide. Thirteen people were killed and five were injured as a result of the earthquake. Eighty-six houses were totally destroyed and 260 were heavily damaged. The harbor facilities were almost completely destroyed, and the entire economic base of the town was wiped out. The total cost to replace the destroyed public and private facilities was estimated at $22 million. Seward lies on the axis of the Chugach Mountains geosyncline. The main structural trend in the mapped area, where the rocks consist almost entirely of graywacke and phyllite, is from near north to N. 20° E. Beds and cleavage of the rocks commonly dip 70° W. or NW. to near vertical. Locally, the rocks are complexly folded or contorted. So major faults were found in the mapped area, but small faults, shear zones, and joints are common. Surficial deposits of the area hare been divided for mapping into the following units: drift deposits, alluvial fan deposits, valley alluvium, intertidal deposits, landslide deposits, and artificial fill. Most of these units intergrade and were deposited more or less contemporaneously. The drift deposits consist chiefly of till that forms moraines along the lower flanks of the Resurrection River valley and up tributary valleys. The till is predominantly silt and sand and lesser amounts of clay-size particles, gravel, cobbles, and boulders. Glacial outwash and stratified ice-contact deposits constitute the remainder of the drift deposits. Fans and fan-deltas have been deposited at the valley mouths of tributary streams. Some, including the one upon which Seward built, project into Resurrection Bay, and deltaic-type deposits form their distal edges. The larger fans—composed chiefly of loosely compacted and poorly sorted silt, sand, and gravel—form broad aprons having low gradients. The fan deposits range in thickness from about 100 feet to possibly several hundred feet and, at least in some places, lie on a platform of compact drift. Smaller fans at the mouths of several canyons have steep gradients and considerable local relief. Valley alluvium, deposited chiefly by the Resurrection River, consists mostly of coarse sand and fine to medium gravel. In the axial part of the valley it is probably more than 100 feet thick. Near the head of Resurrection Bay, the alluvium is underlain by at least 75 feet of marine deltaic sediments, which are in turn underlain by 600 or more feet of drift in the deepest part of the bedrock valley. Beach, deltaic, and estuarine sediments, deposited on intertidal flats at the head of the bay and along far1 margins that extend into the bay, arc mapped as intertidal deposits. They consist mostly of silt, sand, and fine gravel, and lesser amounts of clay-size particles. The earthquake reactivated old slides and trigged new ones in the mountains. Rock and snow avalanches, debris flows, and creep of talus deposits characterized slide activity on the steeper slops. The Seward waterfront had been extended before the earthquake by adding artificial fill consisting of loose sand and gravel; part of the lagoon area had been filled with refuse. After the earth- quake, fill, consisting of silt and sand dredged from the head of the bay, was pumped onto part of the lagoon area and also on land at the northwest corner of the bay. Response to the disaster was immediate and decisive. City, State, and Federal agencies, as well as other organizations and individuals, gave unstintingly of their time and facilities. Within a few days, there was temporary restoration of water, sewerage, and electrical facilities. The U.S. Army Corps of Engineers was authorized to select sites and construct a new dock for the Alaska Railroad, a new small-boat basin, and related facilities. The firm of Shannon and Wilson, Inc., under contract to the Corps of Engineers, investigated subsurface soils extensively to determine the factors responsible for the sliding along the Seward waterfront and to assist in site selection for reconstruction of the destroyed harbor facilities. Borings also made along the Seward waterfront and at the head of the bay, and laboratory tests were conducted on pertinent samples. These studies were augmented by geophysical studies both on land and in the bay. In addition, the Corps of Engineers made shallow borings on the intertidal flats at the head of the bay and performed pile-driving and load tests. Borings also were drilled and test pits were dug in the subdivision of Forest Acres. Sliding along the Seward waterfront markedly deepened the water along the former shoreline. Post-earthquake slopes of the bay floor immediately offshore also are steeper in places than before the earthquake. The strong ground motion of the earthquake triggered the landsliding, but several factors may have contributed to the magnitude and characteristics of the slides. These factors are: (1) the long duration of strong ground motion, (2) the grain size and texture of the material involved in the sliding, (3) the probability that the finer grained materials liquefied and flowed seaward, and (4) the added load of manmade facilities built on the edge of the shore, Secondary effects of the slides themselves—sudden drawdown of water, followed by the weight of returning waves—also may have contributed to the destruction. Submarine sliding at the northwest corner of the bay occurred in fine-grained deltaic deposits whose frontal slopes probably were in metastable equilibrium under static conditions. Uplift pressures from aquifers under hydrostatic head, combined with the probable liquefaction characteristics of the sediments when vibrated by strong ground motion, probably caused the material to slide and flow seaward as a heavy slurry. Under static conditions, no major shoreline or submarine landsliding is expected in the Seward area; in the event of another severe earthquake, however, additional sliding is likely along the Seward waterfront and also in the deltaic deposits at the northwest corner of the bay. Fractured ground in back of the present shoreline along the Seward waterfront is an area of incipient landslides that would be unstable under strong shaking. For this reason the Scientific and Engineering Task Force placed the area in a high-risk classification and recommended no repair, rehabilitation, or new construction in this area involving use of Federal funds; it was further recommended that the area should be reserved for park or other uses that do not involve large congregations of people. The deltaic deposits at the head of the bay probably also would be susceptible to sliding during another large earthquake. This sliding would result in further landward retreat of the present shoreline toward the new railroad dock. Specifications for the new dock, whose seaward end is now approximately 1,100 feet from the back scarp of the subaqueous landslide, require design pro- visions to withstand seismic shock up to certain limits. Earthquake-induced fracturing of the ground in the subdivision of Forest Acres was confined to the lower part of a broad alluvial fan. There, sewer and water lines were ruptured and the foundations of some homes were heavily damaged. Landsliding, such as occurred along the shoreline of the bay, was not a contributing cause of the fracturing. Two hypotheses are offered to explain the fracturing: 1. Seismic energy was transformed into visible surface waves of such amplitude that the strength of surface layer was exceeded and rupturing occurred; tensional and compressional stresses alternately opened and closed the fractures and forced out water and mud. 2. Compaction by vibration of the fine-grained deposits of the fan caused ground settlement and fracturing; ground water under temporary hydrostatic head was forced to the surface as fountains and carried the finer material with it. Water waves that crashed onto shore, while shaking was still continuing, were generated chiefly by onshore and offshore landsliding. Waves that overran the shores about 25 minutes after shaking stopped and that continued to arrive for the next several hours are believed to be seismic sea waves (tsunamis) that originated in an uplifted area in the Gulf of Alaska. During the time of seismic sea-wave activity and perhaps preceding it, seiche wares also may have been generated within Resurrection Bay and complicated the wave effects along the shoreline.

Alaska↗
USGS2014

Coastal geology and recent origins for Sand Point, Lake Superior

Sand Point is a small cuspate foreland located along the southeastern shore of Lake Superior within Pictured Rocks National Lakeshore near Munising, Michigan. Park managers’ concerns for the integrity of historic buildings at the northern periphery of the point during the rising lake levels in the mid-1980s greatly elevated the priority of research into the geomorphic history and age of Sand Point. To pursue this priority, we recovered sediment cores from four ponds on Sand Point, assessed subsurface stratigraphy onshore and offshore using geophysical techniques, and interpreted the chronology of events using radiocarbon and luminescence dating. Sand Point formed at the southwest edge of a subaqueous platform whose base is probably constructed of glacial diamicton and outwash. During the post-glacial Nipissing Transgression, the base was mantled with sand derived from erosion of adjacent sandstone cliffs. An aerial photograph time sequence, 1939–present, shows that the periphery of the platform has evolved considerably during historical time, infl uenced by transport of sediment into adjacent South Bay. Shallow seismic refl ections suggest slump blocks along the leading edge of the platform. Light detection and ranging (LiDAR) and shallow seismic refl ections to the northwest of the platform reveal large sand waves within a deep (12 m) channel produced by currents fl owing episodically to the northeast into Lake Superior. Ground-penetrating radar profi les show transport and deposition of sand across the upper surface of the platform. Basal radiocarbon dates from ponds between subaerial beach ridges range in age from 540 to 910 cal yr B.P., suggesting that Sand Point became emergent during the last ~1000 years, upon the separation of Lake Superior from Lakes Huron and Michigan. However, optically stimulated luminescence (OSL) ages from the beach ridges were two to three times as old as the radiocarbon ages, implying that emergence of Sand Point may have begun earlier, ~2000 years ago. The age discrepancy appears to be the result of incomplete bleaching of the quartz grains and an exceptionally low paleodose rate for the OSL samples. Given the available data, the younger ages from the radiocarbon analyses are preferred, but further work is necessary to test the two age models.

Michigan↗
USGS2024

Large eddy simulation of cross-shore hydrodynamics under random waves in the inner surf and swash zones

A 3D large eddy simulation coupled with a free surface tracking scheme was used to simulate cross-shore hydrodynamics as observed in a large wave flume experiment. The primary objective was to enhance the understanding of wave-backwash interactions and the implications for observed morphodynamics. Two simulation cases were carried out to elucidate key processes of wave-backwash interactions across two distinct stages: berm erosion and sandbar formation, during the early portion of a modeled storm. The major difference between the two cases was the bathymetry: one featuring a berm without a sandbar (Case I), and the other, featuring a sandbar without a berm (Case II) at similar water depth. Good agreement (overall Willmott's index of agreement greater than 0.8) between simulations and measured data in free surface elevation, wave spectrum, and flow velocities validated the model skill. The findings indicated that the bottom shear stress, represented by the Shields parameter, was significant in both cases, potentially contributing substantial sediment transport. Notably, the occurrence of intense wave-backwash interactions were more frequent in the absence of a sandbar. These intense wave-backwash interactions resulted in a pronounced horizontal pressure gradient, quantified by high Sleath parameters, exceeding the criteria for momentary bed failure. Additionally, a more vigorous turbulence-bed interaction, characterized by near-bed turbulent kinetic energy, was observed in the case lacking a sandbar, potentially augmenting sediment suspension. These insights are pivotal in understanding the mechanisms underlying berm erosion and how sandbar formation serves to protect further beach erosion.

JGR Oceans↗
USGS2018

California State Waters Map Series — Offshore of Gaviota, California

Introduction In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow subsurface geology. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and the region is presently undergoing north-south shortening. The offshore part of the map area lies south of the steep south flank of the Santa Ynez M ountains . The crest of the range , which has a maximum elevation of about 760 m in the map area , lies about 4 km north of the shoreline. Gaviota is an unincorporated community that has a sparse population (less than 100), and the coastal zone is largely open space that is locally used for cattle grazing. The Union Pacific railroad tracks extend westward along the coast through the entire map area, within a few hundred meters of the shoreline. Highway 101 crosses the eastern part of the map area, also along the coast, then turns north (inland) and travels through Cañada de la Gaviota and Gaviota Pass en route to Buellton. Gaviota State Park lies at the mouth of Cañada de la Gaviota. West of Gaviota, the onland coastal zone is occupied by the Hollister Ranch, a privately owned, gated community that has no public access. The map area has a long history of petroleum exploration and development. Several offshore gas fields were discovered and were developed by onshore directional drilling in the 1950s and 1960s. Three offshore petroleum platforms were installed in adjacent federal waters in 1976 (platform “Honda”) and 1989 (platforms “Heritage” and “Harmony”). Local offshore and onshore operations were serviced for more than a century by the Gaviota marine terminal, which is currently being decommissioned and will be abandoned in an intended transition to public open space. The Offshore of Gaviota map area lies within the western Santa Barbara Channel region of the Southern California Bight, and it is somewhat protected from large Pacific swells from the north and northwest by Point Conception and from south and southwest swells by offshore islands and banks. Much of the shoreline in the map area is characterized by narrow beaches that have thin sediment cover, backed by low (10- to 20-m-high) cliffs that are capped by a narrow coastal terrace. Beaches are subject to wave erosion during winter storms, followed by gradual sediment recovery or accretion in the late spring, summer, and fall months during the gentler wave climate. The map area lies in the western-central part of the Santa Barbara littoral cell, which is characterized by west-to-east transport of sediment from Point Arguello on the northwest to Hueneme and Mugu Canyons on the southeast. Sediment supply to the western and central part of the littoral cell is mainly from relatively small coastal watersheds. In the map area, sediment sources include Cañada de la Gaviota (52 km 2 ), as well as Cañada de la Llegua, Arroyo el Bulito, Cañada de Santa Anita, Cañada de Alegria, Cañada del Agua Caliente, Cañada del Barro, Cañada del Leon, Cañada San Onofre, and many others. Coastal-watershed discharge and sediment load are highly variable, characterized by brief large events during major winter storms and long periods of low (or no) flow and minimal sediment load between storms. In recent (recorded) history, the majority of high-discharge, high-sediment-flux events have been associated with El Niño phases of the El Niño–Southern Oscillation climatic pattern. Shelf width in the Offshore of Gaviota map area ranges from about 4.3 to 4.7 km, and shelf slopes average about 1.0° to 1.2° but are highly variable because of the presence of the large Gaviota sediment bar. This bar extends southwestward for about 9 km from the mouth of Cañada de la Gaviota to the shelf break, is as wide as 2 km, and is by far the largest shore-attached sediment bar in the Santa Barbara Channel. The shelf is underlain by bedrock and variable amounts (0 to as much as 36 m in the Gaviota bar) of upper Quaternary sediments deposited as sea level fluctuated in the late Pleistocene. The trend of the shelf break changes from about 276° to 236° azimuth over a distance of about 12 km, and it ranges in depth from about 91 m to as shallow as 62 to 73 m where significant shelf-break and upper-slope failure and landsliding has apparently occurred. The shelf break in the western part of the map area is notably embayed by the heads of three large (150- to 300-m-wide) channels that have been referred to as “the Gaviota Canyons” or as “Drake Canyon,” “Sacate Canyon,” and “Alegria Canyon.” Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft, unconsolidated sediment interspersed with isolated areas of rocky habitat that support kelp-forest communities in the nearshore and rocky-reef communities in deeper water. The potential marine benthic habitat types mapped in the Offshore of Gaviota map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank or continental slope) megahabitats. The fairly homogeneous seafloor of sediment and low-relief bedrock provides characteristic habitat for rockfish, groundfish, crabs, shrimp, and other marine benthic organisms. Several areas of smooth sediment form nearshore terraces that have relatively steep, smooth fronts, which may be attractive to groundfish. Below the steep shelf break, soft, unconsolidated sediment is interrupted by the heads of several submarine canyons and rills, some bedrock exposures, and small carbonate mounds associated with asphalt mounds and pockmarks, also good potential habitat for rockfish. The map area includes the relatively small (5.2 km 2 ) Kashtayit State Marine Conservation Area, which largely occupies the inner part of the Gaviota sediment bar.

California↗
USGS2002

Post-glacial inflation-deflation cycles, tilting, and faulting in the Yellowstone Caldera based on Yellowstone Lake shorelines

The Yellowstone caldera, like many other later Quaternary calderas of the world, exhibits dramatic unrest. Between 1923 and 1985, the center of the Yellowstone caldera rose nearly one meter along an axis between its two resurgent domes (Pelton and Smith, 1979, Dzurisin and Yamashita, 1987). From 1985 until 1995-6, it subsided at about two cm/yr (Dzurisin and others, 1990). More recent radar interferometry studies show renewed inflation of the northeastern resurgent dome between 1995 and 1996; this inflation migrated to the southwestern resurgent dome from 1996 to 1997 (Wicks and others, 1998). We extend this record back in time using dated geomorphic evidence of postglacial Yellowstone Lake shorelines around the northern shore, and Yellowstone River levels in the outlet area. We date these shorelines using carbon isotopic and archeological methods. Following Meyer and Locke (1986) and Locke and Meyer (1994), we identify the modern shoreline as S1 (1.9 ? 0.3 m above the lake gage datum), map paleoshoreline terraces S2 to S6, and infer that the prominent shorelines were cut during intracaldera uplift episodes that produced rising water levels. Doming along the caldera axis reduces the gradient of the Yellowstone River from Le Hardys Rapids to the Yellowstone Lake outlet and ultimately causes an increase in lake level. The 1923-1985 doming is part of a longer uplift episode that has reduced the Yellowstone River gradient to a ?pool? with a drop of only 0.25 m over most of this 5 km reach. We also present new evidence that doming has caused submergence of some Holocene lake and river levels. Shoreline S5 is about 14 m above datum and estimated to be ~12.6 ka, because it post-dates a large hydrothermal explosion deposit from the Mary Bay area (MB-II) that occurred ~13 ka. S4 formed about 8 m above datum ~10.7 ka as dated by archeology and 14C, and was accompanied by offset on the Fishing Bridge fault. About 9.7 ka, the Yellowstone River eroded the ?S-meander?, followed by a ~5 m rise in lake level to S2. The lowest generally recognizable shoreline is S2. It is ~5 m above datum (3 m above S1) and is ~8 ka, as dated on both sides of the outlet. Yellowstone Lake and the river near Fishing Bridge were 5-6 m below their present level about 3-4 ka, as indicated by 14C ages from submerged beach deposits, drowned valleys, and submerged Yellowstone River gravels. Thus, the lake in the outlet region has been below or near its present level for about half the time since a 1 km-thick icecap melted from the Yellowstone Lake basin about 16 ka. The amplitude of two rises in lake and river level can be estimated based on the altitude of Le Hardys Rapids, indicators of former lake and river levels, and reconstruction of the river gradient from the outlet to Le Hardys Rapids. Both between ~9.5 ka and ~8.5 ka, and after ~3 ka, Le Hardys Rapids (LHR) was uplifted about 8 meters above the outlet, suggesting a cyclic deformation process. Older possible rises in lake level are suggested by locations where the ~10.7 ka S4 truncates older shorelines, and valleys truncated by the ~12.6 ka S5 shoreline. Using these controls, a plot of lake level through time shows 5-7 millennial-scale oscillations since 14.5 ka. Major cycles of inflation and deflation are thousands of years long. Le Hardys Rapids has twice been uplifted ~8 m relative to the lake outlet. These two locations span only the central 25% of the historic caldera doming, so that if we use historic doming as a model, total projected uplift would be ~32 m. This ?heavy breathing? of the central part of the Yellowstone caldera may reflect a combination of several possible processes: magmatic inflation, tectonic stretching and deflation, and hydrothermal fluid sealing and inflation followed by cracking of the seal, pressure release, and deflation. Over the entire postglacial period, subsidence has balanced or slightly exceeded uplift as shown by older shorelines that descend towards the caldera axis. We

Open-File Report↗