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At least 451 records · Page 25Linked to original sources

USGS1973

River channel change with time : An example

Monumented channel cross sections were resurveyed over a period of 20 yrs (1953 to 1972) to determine the amount and kind of change of channel area and position on a 3.7-sq-mi basin, Watts Branch near Rockville, Maryland. For the first 12 yrs, the channel progressively but slowly became smaller as urbanization of the basin gradually proceeded. After 1966, a threshold of change apparently was passed and, probably as a result of an increased rate of land alteration upstream, large amounts of sediment were deposited within the channel and overbank. The number of floods exceeding channel capacity increased dramatically from an average of two to more than ten per year. Simultaneously, the channel area began to increase. Despite the trend toward increasing cross-sectional area, the net result after 20 yrs was a channel smaller by 20 percent than it had been originally. Urbanization did not alter the rate of channel migration.

Maryland↗

USGS1981

Rare-earth element geochemistry of the island-arc volcanic rocks of Rabaul and Talasea, New Britain

The island-arc volcanic rocks of Rabaul and Talasea, New Britain, range in composition from basalt through rhyolite. Rare-earth elements have been determined by mass-spectrometric isotope dilution in 16 samples. Chondrite-normalized rare-earth element patterns are distinct for each volcanic center, but all are relatively flat (Ce/Yb E.F. = 1.1 to 3.0). Within each center, rare-earth element concentrations increase from basalt to dacite, and Eu anomalies become progressively more negative from basalt to dacite (Eu/Eu* = 1.0 to 0.8). Lavas inferred to contain cumulate phenocrysts show positive Eu anomalies (Eu/Eu* of up to 1.2). The observed variations are consistent with fractional crystallization of basalt or basaltic andesite by removal or accumulation of the observed phenocrysts, including olivine, plagioclase, pyroxene, and opaque minerals. Quantitative trace-element models for Talasea lavas indicate precipitation of 50 wt percent of phenocrysts from basalt to produce andesite and an additional 22 wt percent to produce dacite. A total-equilibrium model provides the best approximation to observed concentrations, implying that the process took place at a depth sufficient to allow slow cooling of the magma as precipitation proceeded. The “least fractionated” basalts and basaltic andesites are similar in rare-earth element pattern to those of corresponding type suites in other oceanic-island arcs, implying a widespread uniformity of source and process in the production of each magma type.

Geological Society of America Bulletin↗

USGS1994

Karstification without carbonic acid: Bedrock dissolution by gypsum- driven dedolomitization

Aggressive karstification can take place where dolomite and gypsum are in contact with the same aquifer. Gypsum dissolution drives the precipitation of calcite, thus consuming carbonate ions released by dolomite. Lake Banyoles, in northeastern Spain, is a karst lake supplied by sublacustrine springs, and karstic collapse is occurring in the immediate vicinity of the lake. Lake water is dominated by Mg-Ca and SO 4 -HCO 3 , and is supersaturated with calcite that is actively accumulating in lake sediments. Water chemistry, sulfur isotope composition, local stratigraphy, and mass-balance modelling suggest that the primary karst-forming process at at Lake Banyoles is dedolomitization of basement rocks driven by gypsum dissolution. Karstification takes place along the subsurface contact between the gypsiferous Beuda Formation and the dolomitic Perafita Formation. This process is here recognized for the first time to cause karstification on a large scale; this is significant because it proceeds without the addition of soil-generated carbonic acid. Gypsum-driven dedolomitization may be responsible for other karstic systems heretofore attributed to soil-generated carbonic acid.

Geology↗

USGS2007

Mining-impacted sources of metal loading to an alpine stream based on a tracer-injection study, Clear Creek County, Colorado

Base flow water in Leavenworth Creek, a tributary to South Clear Creek in Clear Creek County, Colorado, contains copper and zinc at levels toxic to aquatic life. The metals are predominantly derived from the historical Waldorf mine, and sources include an adit, a mine-waste dump, and mill-tailings deposits. Tracer-injection and water-chemistry synoptic studies were conducted during low-flow conditions to quantify metal loads of mining-impacted inflows and their relative contributions to nearby Leavenworth Creek. During the 2-year investigation, the adit was rerouted in an attempt to reduce metal loading to the stream. During the first year, a lithium-bromide tracer was injected continuously into the stream to achieve steady-state conditions prior to synoptic sampling. Synoptic samples were collected from Leavenworth Creek and from discrete surface inflows. One year later, synoptic sampling was repeated at selected sites to evaluate whether rerouting of the adit flow had improved water quality. The largest sources of copper and zinc to the creek were from surface inflows from the adit, diffuse inflows from wetland areas, and leaching of dispersed mill tailings. Major instream processes included mixing between mining- and non-mining-impacted waters and the attenuation of iron, aluminum, manganese, and othermetals by precipitation or sorption. One year after the rerouting, the Zn and Cu loads in Leavenworth Creek from the adit discharge versus those from leaching of a large volume of dispersed mill tailings were approximately equal to, if not greater than, those before. The mine-waste dump does not appear to be a major source of metal loading. Any improvement that may have resulted from the elimination of adit flow across the dump was masked by higher adit discharge attributed to a larger snow pack. Although many mine remediation activities commonly proceed without prior scientific studies to identify the sources and pathways of metal transport, such strategies do not always translate to water-quality improvements in the stream. Assessment of sources and pathways to gain better understanding of the system is a necessary investment in the outcome of any successful remediation strategy.

Colorado↗

USGS2009

Supply and dispersal of flood sediment from a steep, tropical watershed: Hanalei Bay, Kauai, Hawaii, USA

In contrast to many small, mountainous watersheds in temperate coastal regions, where fluvial discharge and wave energy commonly coincide, deposition and reworking of tropical flood sediment can be seasonally decoupled, and this has important implications for coral-reef ecosystems. An understanding of the interaction between tropical flood sedimentation and wave climate is essential to identifying and mitigating effects of watershed changes on coral reefs as urbanization and climate change proceed. Sedimentary facies and isotopic properties of sediment in Hanalei Bay, on the island of Kaua'i, Hawai'i, USA, were used to assess deposition and reworking of flood deposits from the Hanalei River in a case study demonstrating the potential ecosystem effects of runoff from a steep, tropical watershed. In Hanalei Bay, the youngest and thickest terrigenous sediment was consistently present near the river mouth and in a bathymetric depression that acted as at least a temporary sediment sink. During this 2 yr study, the largest flood events occurred in late winter and spring 2006; substantial terrestrial sediment delivered by those floods still remained in the bay as of June 2006 because oceanic conditions were not sufficiently energetic to transport all of the sediment offshore. Additional sediment was deposited in the bay by a summer 2006 flood that coincided with seasonal low wave energy. In most years, flood sediment accumulating in the bay and on its fringing reefs would be remobilized and advected out of the bay during winter, when the wave climate is energetic. Turbidity and sedimentation on corals resulting from late spring and summer floods during low wave energy could have a greater impact on coral-reef ecosystems than floods in other seasons, an effect that could be exacerbated if the incidence and sediment load of tropical summer floods increase due to urbanization and climate change.

Hawaii↗

USGS2011

Erosion, storage, and transport of sediment in two subbasins of the Rio Puerco, New Mexico

Arroyos in the American Southwest proceed through cut-and-fill cycles that operate at centennial to millennial time scales. The geomorphic community has put much effort into understanding the causes of arroyo cutting in the late Quaternary and in the modern record (late 1800s), while little effort has gone into understanding how arroyos fill and the sources of this fill. Here, we successfully develop a geographic information system (GIS)-modeled sediment budget that is based on detailed field measurements of hillslope and channel erosion and deposition. Field measurements were made in two arroyo basins draining different lithologies and undergoing different land disturbance (Volcano Hill Wash, 9.30 km 2 ; Arroyo Chavez, 2.11 km 2 ) over a 3 yr period. Both basins have incised channels that formed in response to the late nineteenth-century incision of the Rio Puerco. Large volumes of sediment were generated during arroyo incision, equal to more than 100 yr of the current annual total sediment load (bed load + suspended load) in each basin. Downstream reaches in both arroyos are presently aggrading, and the main source of the sediment is from channel erosion in upstream reaches and first- and second-order tributaries. The sediment budget shows that channel erosion is the largest source of sediment in the current stage of the arroyo cycle: 98% and 80% of the sediment exported out of Volcano Hill Wash and Arroyo Chavez, respectively. The geomorphic surface most affected by arroyo incision and one of the most important sediment sources is the valley alluvium, where channel erosion, gullying, soil piping, and grazing all occur. Erosion rates calculated for the entire Volcano Hill Wash (-0.26 mm/yr) and Arroyo Chavez (-0.53 mm/yr) basins are higher than the modeled upland erosion rates in each basin, reflecting the large contributions from channel erosion. Erosion rates in each basin are affected by a combination of land disturbance (grazing) and lithology--erodible sandstones and shales in Arroyo Chavez compared with basalt for Volcano Hill Wash. Despite these differences, hillslope sediment yields are similar to long-term denudation rates. As the arroyo fills over time from mouth to headwaters, hillslope sediment becomes a more significant sediment source.

New Mexico↗

USGS2016

Linking silicate weathering to riverine geochemistry—A case study from a mountainous tropical setting in west-central Panama

Chemical analyses from 71 watersheds across an ∼450 km transect in west-central Panama provide insight into controls on weathering and rates of chemical denudation and CO 2 consumption across an igneous arc terrain in the tropics. Stream and river compositions across this region of Panama are generally dilute, having a total dissolved solute value = 118 ± 91 mg/L, with bicarbonate and silica being the predominant dissolved species. Solute, stable isotope, and radiogenic isotope compositions are consistent with dissolution of igneous rocks present in Panama by meteoric precipitation, with geochemical signatures of rivers largely acquired in their upstream regions. Comparison of a headwater basin with its entire watershed observed considerably more runoff production from the high-elevation upstream portion of the catchment than in its much more spatially extensive downstream region. Rock alteration profiles document that weathering proceeds primarily by dissolution of feldspar and pyroxene, with base cations effectively leached in the following sequence: Na > Ca > Mg > K. Control on water chemistry by bedrock lithology is indicated through a linking of elevated ([Na + K]/[Ca + Mg]) ratios in waters to a high proportion of catchment area silicic bedrock and low ratios to mafic bedrock. Sr-isotope ratios are dominated by basement-derived Sr, with only very minor, if any, contribution from other sources. Cation weathering of Ca sil + Mg sil + Na + K spans about an order in magnitude, from 3 to 32 tons/km 2 /yr. Strong positive correlations of chemical denudation and CO 2 consumption are observed with precipitation, mean watershed elevation, extent of land surface forest cover, and physical erosion rate.

Chagras and Pacora watersheds↗

USGS2002

Overview of catastrophic landslides of South America in the twentieth century

This chapter summarizes the processes and effects of the most notable catastrophic mass movement events in South America in the twentieth century. We present 23 case histories of individual and regional landslide events, beginning at the northeast terminus of the Andes Mountains in Venezuela, proceeding counterclockwise down the Pacific Coast to the southern Andes of Chile and Argentina, and ending with discussion of catastrophic regional mass movements in the Brazilian Highlands. The types of landslides involved in these disasters ranged from high-velocity rockslides and rock or debris avalanches to high-to medium-velocity debris flows and mudflows. Most casualties were caused by high-velocity debris avalanches and high-to medium-velocity, highly mobile, long-runout debris flows. A common, and particularly devastating, regional occurrence consisted of earthquake-triggered slides on steep slopes covered with saturated residual soils; these slides were rapidly transformed into very fluid, high-velocity debris avalanches, which in turn changed into devastating debris flows that ran out into populated areas on valley bottoms.

Reviews in Engineering Geology↗

USGS2000

A hybrid orographic plus statistical model for downscaling daily precipitation in northern California

A hybrid (physical–statistical) scheme is developed to resolve the finescale distribution of daily precipitation over complex terrain. The scheme generates precipitation by combining information from the upper-air conditions and from sparsely distributed station measurements; thus, it proceeds in two steps. First, an initial estimate of the precipitation is made using a simplified orographic precipitation model. It is a steady-state, multilayer, and two-dimensional model following the concepts of Rhea. The model is driven by the 2.5° × 2.5° gridded National Oceanic and Atmospheric Administration–National Centers for Environmental Prediction upper-air profiles, and its parameters are tuned using the observed precipitation structure of the region. Precipitation is generated assuming a forced lifting of the air parcels as they cross the mountain barrier following a straight trajectory. Second, the precipitation is adjusted using errors between derived precipitation and observations from nearby sites. The study area covers the northern half of California, including coastal mountains, central valley, and the Sierra Nevada. The model is run for a 5-km rendition of terrain for days of January–March over the period of 1988–95. A jackknife analysis demonstrates the validity of the approach. The spatial and temporal distributions of the simulated precipitation field agree well with the observed precipitation. Further, a mapping of model performance indices (correlation coefficients, model bias, root-mean-square error, and threat scores) from an array of stations from the region indicates that the model performs satisfactorily in resolving daily precipitation at 5-km resolution.

California↗

USGS2015

Using near-real-time monitoring data from Pu'u 'Ō'ō vent at Kīlauea Volcano for training and educational purposes

Training non-scientists in the use of volcano-monitoring data is critical preparation in advance of a volcanic crisis, but it is currently unclear which methods are most effective for improving the content-knowledge of non-scientists to help bridge communications between volcano experts and non-experts. We measured knowledge gains for beginning-(introductory-level students) and novice-level learners (students with a basic understanding of geologic concepts) engaged in the Volcanoes Exploration Program: Pu‘u ‘Ō‘ō (VEPP) “Monday Morning Meeting at the Hawaiian Volcano Observatory” classroom activity that incorporates authentic Global Positioning System (GPS), tilt, seismic, and webcam data from the Pu‘u ‘Ō‘ō eruptive vent on Kīlauea Volcano, Hawai‘i (NAGT website, 2010), as a means of exploring methods for effectively advancing non-expert understanding of volcano monitoring. Learner groups consisted of students in introductory and upper-division college geology courses at two different institutions. Changes in their content knowledge and confidence in the use of data were assessed before and after the activity using multiple-choice and open-ended questions. Learning assessments demonstrated that students who took part in the exercise increased their understanding of volcano-monitoring practices and implications, with beginners reaching a novice stage, and novices reaching an advanced level (akin to students who have completed an upper-division university volcanology class). Additionally, participants gained stronger confidence in their ability to understand the data. These findings indicate that training modules like the VEPP: Monday Morning Meeting classroom activity that are designed to prepare non-experts for responding to volcanic activity and interacting with volcano scientists should introduce real monitoring data prior to proceeding with role-paying scenarios that are commonly used in such courses. The learning gains from the combined approach will help improve effective communications between volcano experts and non-experts during times of crisis, thereby reducing the potential for confusion and misinterpretation of data.

Hawaii↗

USGS2021

DAS 3DVSP survey at Stratigraphic Test Well (Hydrate-01)

This proceeding outlines the acquisition, processing, and fault interpretation of the largest known onshore distributed acoustic sensing (DAS) 3D vertical seismic profile (VSP) survey. This survey was carried out to detect the distribution of faults near the gas hydrate research well (Stratigraphic Test Well: Hydrate-01) on the North Slope of Alaska within the Prudhoe Bay Unit (PBU). The data were recorded with a single-mode DAS cable which is permanently installed and cemented behind the casing of the Hydrate-01 well. A total of 1701 shot records were successfully acquired in 12 days using a DAS interrogator with two vibroseis sources. The data were converted from strain rate to a geophone equivalent for further data processing. Traveltime tomography was carried out using the first break of each shot and was used to build a 3D tilted transverse isotropy (TTI) velocity model. The data were processed with a sequence designed to produce a precise and high resolution P wave image, that included editing, redatum, band pass filtering, denoise, upgoing / downgoing wavefield separation, deconvolution and migration. Faults around the Hydrate-01 were interpreted using the 3DVSP volume and its attributes. These faults were clearly observed in the 3DVSP volume but they cannot be recognized by an existing 3D surface seismic volume.

Conference Paper↗

USGS2004

Surface rupture of the 2002 Denali fault, Alaska, earthquake and comparison with other strike-slip ruptures

On 3 November 2002, an M7.9 earthquake produced 340 km of surface rupture on the Denali and two related faults in Alaska. The rupture proceeded from west to east and began with a 40-km-long break on a previously unknown thrust fault. Estimates of surface slip on this thrust are 3-6 m. Next came the principal surface break along ???218 km of the Denali fault. Right-lateral offsets averaged around 5 m and increased eastward to a maximum of nearly 9 m. The fault also ruptured beneath the trans-Alaska oil pipeline, which withstood almost 6 m of lateral offset. Finally, slip turned southeastward onto the Totschunda fault. Right-lateral offsets are up to 3 m, and the surface rupture is about 76 km long. This three-part rupture ranks among the longest strike-slip events of the past two centuries. The earthquake is typical when compared to other large earthquakes on major intracontinental strike-slip faults. ?? 2004, Earthquake Engineering Research Institute.

Earthquake Spectra↗

USGS2001

Alaska: A twenty-first-century petroleum province

Alaska, the least explored of all United States regions, is estimated to contain approximately 40% of total U.S. undiscovered, technically recoverable oil and natural-gas resources, based on the most recent U.S. Department of the Interior (U.S. Geological Survey and Minerals Management Service) estimates. Northern Alaska, including the North Slope and adjacent Beaufort and Chukchi continental shelves, holds the lion's share of the total Alaskan endowment of more than 30 billion barrels (4.8 billion m 3 ) of oil and natural-gas liquids plus nearly 200 trillion cubic feet (5.7 trillion m 3 ) of natural gas. This geologically complex region includes prospective strata within passive-margin, rift, and foreland-basin sequences. Multiple source-rock zones have charged several regionally extensive petroleum systems. Extensional and compressional structures provide ample structural objectives. In addition, recent emphasis on stratigraphic traps has demonstrated significant resource potential in shelf and turbidite systems in Jurassic to Tertiary strata. Despite robust potential, northern Alaska remains a risky exploration frontier - a nexus of geologic complexity, harsh economic conditions, and volatile policy issues. Its role as a major petroleum province in this century will depend on continued technological innovations, not only in exploration and drilling operations, but also in development of huge, currently unmarketable natural-gas resources. Ultimately, policy decisions will determine whether exploration of arctic Alaska will proceed.

Alaska↗

USGS2024

Hydrothermal reactivity of saponite

Saponite crystallizes from amorphous gel having an ideal saponite composition within 7 days at all experimental temperatures between 300° and 550°C at 1 kbar pressure. Reactions subsequent to this initial crystallization vary in type and degree, depending on the temperature of reaction and the type of interlayer cation. Above 450°C the intitially crystallized K-saponite dissolves, and talc and phlogopite nucleate and grow as discrete phases. At 450°C the initial K-saponite reacts to form talc and phlogopite layers, but the reaction proceeds via intracrystalline layer transformations rather than via dissolution and precipitation, producing a mixture of fully ordered, interstratified talc/saponite and fully ordered saponite/ phlogopite. The K-saponite shows subtle signs of reaction at 400°C after 200 days: this temperature is at least 150°C lower than experimental reaction temperatures previously reported for saponites. No reactions beyond the initial crystallization of saponite were observed below 400°C. K-saponite reacts more rapidly than either Na-saponite or Ca-saponite above 400°C and the Na-saponite and Ca-saponite produce no mica iayers during their transformation to mixed-layer clays. Interstratified talc/saponite formed in the Na-saponite system, and the Ca-saponite system produced both talc/saponite and chlorite/saponite.

Clays and Clay Minerals↗

USGS2014

Adaptive management and the value of information: learning via intervention in epidemiology

Optimal intervention for disease outbreaks is often impeded by severe scientific uncertainty. Adaptive management (AM), long-used in natural resource management, is a structured decision-making approach to solving dynamic problems that accounts for the value of resolving uncertainty via real-time evaluation of alternative models. We propose an AM approach to design and evaluate intervention strategies in epidemiology, using real-time surveillance to resolve model uncertainty as management proceeds, with foot-and-mouth disease (FMD) culling and measles vaccination as case studies. We use simulations of alternative intervention strategies under competing models to quantify the effect of model uncertainty on decision making, in terms of the value of information, and quantify the benefit of adaptive versus static intervention strategies. Culling decisions during the 2001 UK FMD outbreak were contentious due to uncertainty about the spatial scale of transmission. The expected benefit of resolving this uncertainty prior to a new outbreak on a UK-like landscape would be £45–£60 million relative to the strategy that minimizes livestock losses averaged over alternate transmission models. AM during the outbreak would be expected to recover up to £20.1 million of this expected benefit. AM would also recommend a more conservative initial approach (culling of infected premises and dangerous contact farms) than would a fixed strategy (which would additionally require culling of contiguous premises). For optimal targeting of measles vaccination, based on an outbreak in Malawi in 2010, AM allows better distribution of resources across the affected region; its utility depends on uncertainty about both the at-risk population and logistical capacity. When daily vaccination rates are highly constrained, the optimal initial strategy is to conduct a small, quick campaign; a reduction in expected burden of approximately 10,000 cases could result if campaign targets can be updated on the basis of the true susceptible population. Formal incorporation of a policy to update future management actions in response to information gained in the course of an outbreak can change the optimal initial response and result in significant cost savings. AM provides a framework for using multiple models to facilitate public-health decision making and an objective basis for updating management actions in response to improved scientific understanding.

PLoS Biology↗

USGS2010

Wayward youth: Trans-Beringian movement and differential southward migration by juvenile sharp-tailed sandpipers

The sharp-tailed sandpiper ( Calidris acuminata ) is a long-distance migrant that travels each year from breeding grounds in the Russian Arctic to nonbreeding areas in Australasia. Most adults migrate rapidly from breeding grounds along a largely inland route through Asia. Here we report on the highly unusual migratory strategy of this species in which some juveniles, but virtually no adults, take a pronounced detour to western Alaska before proceeding on southward migration. We analyzed data from our own studies in this region and published and unpublished observations and specimen records of sharptailed sandpipers from the entire Pacific Basin. Each autumn, sharp-tailed sandpipers began arriving on coastal graminoid meadows and intertidal habitats throughout western Alaska during the last half of August and the last sandpipers departed from southwestern Alaska during October and November. Body mass of birds banded or collected across multiple years and sites in western Alaska ( n = 330) increased by an average of 0.57 ± 0.06 g per day between mid-August and late October. Records suggest a small, regular movement of juveniles (and a very few adults) along the Asiatic coast, but we estimate from surveys that a few tens of thousands of juveniles stage in western Alaska each autumn. The distribution of sight and specimen records from the Pacific Basin during autumn suggests strongly age-segregated migration routes, with the principal migration of juveniles crossing central and western Oceania in a possible nonstop trans-Pacific flight from Alaska. This is only the second well-documented case of differential migration among birds that involves different routes for adults and juveniles, and it raises intriguing questions about how and why this system has evolved.

Arctic↗

USGS1999

The epipelagic fish community of Beaufort Sea coastal waters, Alaska

A three-year study of epipelagic fishes inhabiting Beaufort Sea coastal waters in Alaska documented spatial and temporal patterns in fish distribution and abundance and examined their relationships to thermohaline features during summer. Significant interannual, seasonal, and geographical differences in surface water temperatures and salinities were observed. In 1990, sea ice was absent and marine conditions prevailed, whereas in 1988 and 1991, heavy pack ice was present and the dissolution of the brackish water mass along the coast proceeded more slowly. Arctic cod, capelin, and liparids were the most abundant marine fishes in the catches, while arctic cisco was the only abundant diadromous freshwater species. Age-0 arctic cod were exceptionally abundant and large in 1990, while age-0 capelin dominated in the other years. The alternating numerical dominances of arctic cod and age-0 capelin may represent differing species' responses to wind-driven oceanographic processes affecting growth and survival. The only captures of age-0 arctic cisco occurred during 1990. Catch patterns indicate they use a broad coastal migratory corridor and tolerate high salinities. As in the oceanographic data, geographical and temporal patterns were apparent in the fish catch data, but in most cases these patterns were not statistically testable because of excessive zero catches. The negative binomial distribution appeared to be a suitable statistical descriptor of the aggregated catch patterns for the more common species.

Alaska↗

USGS2004

Fire as an ecological process

This chapter investigates fire as a dynamic ecosystem process by first investigating fire in the context of general ecological theory, then discussing the concept of fire regimes, and finally by developing and applying a new framework for classifying fire regimes that better allows for the understanding of the patterns of fire as processes within ecosystems. Moreover, the chapter covers the succession theory and then proceeds through ecosystem, disturbance, and hierarchical theory. Next, it greatly expands on Agee’s (1993) treatment of conceptual distributions to include seven fire regime attributes, namely seasonality, fire return interval, fire size, spatial complexity, fireline intensity, fire severity, and fire type. Although humans have altered fire regimes throughout California for thousands of years, the pace of fire regime change has accelerated over the past 200 years. Recent and current management strategies have imposed directional changes on the pattern of fires in many California ecosystems.

California↗