Geology topics

E. Anderson

Publications and source records attributed to E. Anderson.

5 recordsLinked to original sources

USGS2016

Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake

The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes’ induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.

Science↗

USGS2008

Geological, geochemical, and geophysical studies by the U.S. Geological Survey in Big Bend National Park, Texas

Big Bend National Park (BBNP), Tex., covers 801,163 acres (3,242 km 2 ) and was established in 1944 through a transfer of land from the State of Texas to the United States. The park is located along a 118-mile (190-km) stretch of the Rio Grande at the United States-Mexico border. The park is in the Chihuahuan Desert, an ecosystem with high mountain ranges and basin environments containing a wide variety of native plants and animals, including more than 1,200 species of plants, more than 450 species of birds, 56 species of reptiles, and 75 species of mammals. In addition, the geology of BBNP, which varies widely from high mountains to broad open lowland basins, also enhances the beauty of the park. For example, the park contains the Chisos Mountains, which are dominantly composed of thick outcrops of Tertiary extrusive and intrusive igneous rocks that reach an altitude of 7,832 ft (2,387 m) and are considered the southernmost mountain range in the United States. Geologic features in BBNP provide opportunities to study the formation of mineral deposits and their environmental effects; the origin and formation of sedimentary and igneous rocks; Paleozoic, Mesozoic, and Cenozoic fossils; and surface and ground water resources. Mineral deposits in and around BBNP contain commodities such as mercury (Hg), uranium (U), and fluorine (F), but of these, the only significant mining has been for Hg. Because of the biological and geological diversity of BBNP, more than 350,000 tourists visit the park each year. The U.S. Geological Survey (USGS) has been investigating a number of broad and diverse geologic, geochemical, and geophysical topics in BBNP to provide fundamental information needed by the National Park Service (NPS) to address resource management goals in this park. Scientists from the USGS Mineral Resources and National Cooperative Geologic Mapping Programs have been working cooperatively with the NPS and several universities on several research studies within BBNP. Because the last geologic map of the entire BBNP was published in the 1960s, one of the primary goals of the USGS is to provide a new geologic map of BBNP at a scale 1:100,000; this work is ongoing among the USGS, NPS, the Texas Bureau of Economic Geology, and university scientists. This USGS Circular summarizes eight studies funded and primarily carried out by the USGS, but it is not intended to be a comprehensive reference of work conducted in BBNP. This Circular describes topical research of the recently completed interdisciplinary USGS project, which has provided information leading to a more complete understanding of the following topics in BBNP: Tectonic and geologic history (Chapters 1, 2, and 3), Age and formation processes of a skarn mineral deposit (Chapter 4), Geoenvironmental effects of abandoned mercury mines (Chapter 5), Age, source, and geochemistry of surface and subsurface water resources (Chapter 6), Isotopic tracing of food sources of bears (Chapter 7), and Geophysical characteristics of surface and subsurface geology (Chapter 8). Additional information and the geochemical and geophysical data of the USGS studies in BBNP are available on line at http://minerals.cr.usgs.gov/projects/big_bend/index.html.

Texas↗

USGS2006

Steelhead of the south-central/southern California coast: Population characterization for recovery planning

This report by the National Marine Fisheries Service applies a formal evaluation framework to the problem of delineating Oncorhynchus mykiss populations in the South - Central / Southern California Coast recovery domain, in support of recovery planning under the Endangered Species Act.

NOAA Technical Memorandum↗

USGS2005

Precambrian crystalline basement map of Idaho: An interpretation of aeromagnetic anomalies

Idaho lies within the northern sector of the U.S. Cordillera astride the boundary between the Proterozoic continent (Laurentia) to the east and the Permian to Jurassic accreted terranes to the west. The continental basement is mostly covered by relatively undeformed Mesoproterozoic metasedimentary rocks and intruded or covered by Phanerozoic igneous rocks; accordingly, knowledge of the basement geology is poorly constrained. Incremental knowledge gained since the pioneering studies by W. Lindgren, C.P. Ross, A.L. Anderson, A. Hietanen, and others during the early- and mid-1900's has greatly advanced our understanding of the general geology of Idaho. However, knowledge of the basement geology remains relatively poor, partly because of the remoteness of much of the region plus the lack of a stimulus to decipher the complex assemblage of high-grade gneisses and migmatite of central Idaho. The availability of an updated aeromagnetic anomaly map of Idaho (North American Magnetic Anomaly Group, 2002) provides a means to determine the regional Precambrian geologic framework of the State. The combined geologic and aeromagnetic data permit identification of previously unrecognized crystalline basement terranes, assigned to Archean and Paleoproterozoic ages, and the delineation of major shear zones, which are expressed in the aeromagnetic data as linear negative anomalies (Finn and Sims, 2004). Limited geochronologic data on exposed crystalline basement aided by isotopic studies of zircon inheritance, particularly Bickford and others (1981) and Mueller and others (1995), provide much of the geologic background for our interpretation of the basement geology. In northwestern United States, inhomogeneities in the basement inherited from Precambrian tectogenesis controlled many large-scale tectonic features that developed during the Phanerozoic. Two basement structures, in particular, provided zones of weakness that were repeatedly rejuvenated: (1) northeast-trending ductile shear zones developed on the northwest margin of the Archean Wyoming province during the Paleoproterozoic Trans-Montana orogeny (Sims and others, 2004), and (2) northwest-trending intra-continental faults of the Mesoproterozoic Trans-Rocky Mountain strike-slip fault system (Sims, unpub. data, 2003). In this report, geologic ages are reported in millions of years (Ma) and generalized ages are given in billions of years (Ga). The subdivision of Precambrian rocks used herein is the time classification recommended by the International Union of Geological Sciences (Plumb, 1991).

Idaho↗

USGS2004

Precambrian basement geologic map of Montana– An interpretation of aeromagnetic anomalies

Newly compiled aeromagnetic anomaly data of Montana, in conjunction with the known geologic framework of basement rocks, have been combined to produce a new interpretive geologic basement map of Montana. Crystalline basement rocks compose the basement, but are exposed only in the cores of mountain ranges in southwestern Montana. Principal features deduced from the map are: (1) A prominent northeast-trending, 200-km-wide zone of spaced negative anomalies, which extends more than 700 km from southwestern Montana's Beaverhead Mountains to the Canadian border and reflects suturing of the Archean Mexican Hat Block against the Archean Wyoming Province along the Paleoproterozoic Trans-Montana Orogen (new name) at about 1.9-1.8 Ga; (2) North-northwest-trending magnetic lows in northeastern Montana, which reflect the 1.9-1.8 Ga Trans-Hudson Orogen and truncate the older Trans-Montana Zone; and (3) Subtle northwest- and west-trending negative anomalies in central and western Montana, which represent the northernmost segment of brittle-ductile transcurrent faults of the newly recognized Mesoproterozoic Trans-Rocky Mountain fault system. Structures developed in the Proterozoic provided zones of crustal weakness reactivated during younger Proterozoic and Phanerozoic igneous and tectonic activity. For example, the Trans-Montana Zone guided basement involved thrust faulting in southwestern Montana during the Sevier Orogeny. The Boulder Batholith and associated ore deposits and the linear belt of alkaline intrusions to the northeast were localized along a zone of weakness between the Missouri River suture and the Dillon shear zone of the Trans-Montana Orogen. The northwest-trending faults of Trans-Rocky Mountain system outline depocenters for sedimentary rocks in the Belt Basin. This fault system provided zones of weakness that guided Laramide uplifts during basement crustal shortening. Northwest-trending zones have been locally reactivated during Neogene basin-range extension.

Montana↗