Geology topics

Erin L. Wallin

Publications and source records attributed to Erin L. Wallin.

5 recordsLinked to original sources

USGS2022

Trans-crustal structural control of CO2-rich extensional magmatic systems revealed at Mount Erebus Antarctica

Erebus volcano, Antarctica, with its persistent phonolite lava lake, is a classic example of an evolved, CO 2 -rich rift volcano. Seismic studies provide limited images of the magmatic system. Here we show using magnetotelluric data that a steep, melt-related conduit of low electrical resistivity originating in the upper mantle undergoes pronounced lateral re-orientation in the deep crust before reaching shallower magmatic storage and the summit lava lake. The lateral turn represents a structural fault-valve controlling episodic flow of magma and CO 2 vapour, which replenish and heat the high level phonolite differentiation zone. This magmatic valve lies within an inferred, east-west structural trend forming part of an accommodation zone across the southern termination of the Terror Rift, providing a dilatant magma pathway. Unlike H 2 O-rich subduction arc volcanoes, CO 2 -dominated Erebus geophysically shows continuous magmatic structure to shallow crustal depths of < 1 km, as the melt does not experience decompression-related volatile supersaturation and viscous stalling.

Nature Communications↗

USGS2020

Temporal magnetotellurics reveals mechanics of the 2012 Mount Tongariro, NZ eruption

Monitoring dynamics of volcanic eruptions with geophysics is challenging. In August and November 2012, two small eruptions from Mount Tongariro provided a unique opportunity to image subsurface changes caused by the eruptions. A detailed magnetotelluric survey of the Tongariro volcanic complex completed prior to the eruption (2008–2010) provides the preeruption structure of the magmatic system. A subset of the initial measurement locations was reoccupied in June 2013. Significant changes were observed in phase tensor data at sites close to the eruptive center. Although subsurface electrical resistivity changed, the geometry of the preeruptive reservoir did not. These subsurface resistivity variations are interpreted as being predominantly caused by interaction of partial melt and the overlying brine layer causing volume reduction of the brine layer through phreatic eruption. The ability to detect significant changes associated with the magma reservoir suggests that magnetotellurics can be a valuable volcano monitoring tool.

Mount Tongariro↗

USGS2009

Deep Resistivity Structure of Mid Valley, Nevada Test Site, Nevada

The U.S. Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office (NSO) are addressing ground-water contamination resulting from historical underground nuclear testing through the Environmental Management (EM) program and, in particular, the Underground Test Area (UGTA) project. From 1951 to 1992, 828 underground nuclear tests were conducted at the Nevada Test Site northwest of Las Vegas (DOE UGTA, 2003). Most of these tests were conducted hundreds of feet above the ground-water table; however, more than 200 of the tests were near, or within, the water table. This underground testing was limited to specific areas of the Nevada Test Site including Pahute Mesa, Rainier Mesa/Shoshone Mountain (RM-SM), Frenchman Flat, and Yucca Flat. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Rainier Mesa/Shoshone Mountain (RM-SM) Corrective Action Unit (CAU) (National Security Technologies, 2007). During 2003, the U.S. Geological Survey (USGS), in cooperation with the DOE and NNSA-NSO collected and processed data at the Nevada Test Site in and near Yucca Flat (YF) to help define the character, thickness, and lateral extent of the pre-Tertiary confining units. We collected 51 magnetotelluric (MT) and audio-magnetotelluric (AMT) stations for that research (Williams and others, 2005a, 2005b, 2005c, 2005d, 2005e, and 2005f). In early 2005 we extended that research with 26 additional MT data stations (Williams and others, 2006) located on and near Rainier Mesa and Shoshone Mountain (RM-SM). The new stations extended the area of the hydrogeologic study previously conducted in Yucca Flat, further refining what is known about the pre-Tertiary confining units. In particular, a major goal was to define the extent of the upper clastic confining unit (UCCU). The UCCU is composed of late Devonian to Mississippian siliciclastic rocks assigned to the Eleana Formation and Chainman Shale (National Security Technologies, 2007). The UCCU underlies the Yucca Flat area and extends southwestward toward Shoshone Mountain, westward toward Buckboard Mesa, and northwestward toward Rainier Mesa. Late in 2005 we collected data at an additional 14 MT stations in Mid Valley, CP Hills, and northern Yucca Flat. That work was done to better determine the extent and thickness of the UCCU near the boundary between the southeastern RM-SM CAU and the southwestern YF CAU, and also in the northern YF CAU. The MT data have been released in a separate U.S. Geological Survey report (Williams and others, 2007). The Nevada Test Site magnetotelluric data interpretation presented in this report includes the results of detailed two-dimensional (2-D) resistivity modeling for each profile and inferences on the three-dimensional (3-D) character of the geology within the region.

Nevada↗

USGS2009

Detailed Geophysical Fault Characterization in Yucca Flat, Nevada Test Site, Nevada

Yucca Flat is a topographic and structural basin in the northeastern part of the Nevada Test Site (NTS) in Nye County, Nevada. Between the years 1951 and 1992, 659 underground nuclear tests took place in Yucca Flat; most were conducted in large, vertical excavations that penetrated alluvium and the underlying Cenozoic volcanic rocks. Radioactive and other potential chemical contaminants at the NTS are the subject of a long-term program of investigation and remediation by the U.S. Department of Energy (DOE), National Nuclear Security Administration, Nevada Site Office, under its Environmental Restoration Program. As part of the program, the DOE seeks to assess the extent of contamination and to evaluate the potential risks to humans and the environment from byproducts of weapons testing. To accomplish this objective, the DOE Environmental Restoration Program is constructing and calibrating a ground-water flow model to predict hydrologic flow in Yucca Flat as part of an effort to quantify the subsurface hydrology of the Nevada Test Site. A necessary part of calibrating and evaluating a model of the flow system is an understanding of the location and characteristics of faults that may influence ground-water flow. In addition, knowledge of fault-zone architecture and physical properties is a fundamental component of the containment of the contamination from underground nuclear tests, should such testing ever resume at the Nevada Test Site. The goal of the present investigation is to develop a detailed understanding of the geometry and physical properties of fault zones in Yucca Flat. This study was designed to investigate faults in greater detail and to characterize fault geometry, the presence of fault splays, and the fault-zone width. Integrated geological and geophysical studies have been designed and implemented to work toward this goal. This report describes the geophysical surveys conducted near two drill holes in Yucca Flat, the data analyses performed, and the integrated interpretations developed from the suite of geophysical methodologies utilized in this investigation. Data collection for this activity started in the spring of 2005 and continued into 2006. A suite of electrical geophysical surveys were run in combination with ground magnetic surveys; these surveys resulted in high-resolution subsurface data that portray subsurface fault geometry at the two sites and have identified structures not readily apparent from surface geologic mapping, potential field geophysical data, or surface effects fracture maps.

Open-File Report↗

USGS2007

Magnetotelluric Data, Mid Valley, Nevada Test Site, Nevada

Introduction The United States Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office (NSO) are addressing ground-water contamination resulting from historical underground nuclear testing through the Environmental Management (EM) program and, in particular, the Underground Test Area (UGTA) project. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Rainier Mesa/Shoshone Mountain Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS), in cooperation with the DOE and NNSA-NSO, collected and processed data at the Nevada Test Site in and near Yucca Flat (YF) to help define the character, thickness, and lateral extent of the pre-Tertiary confining units. We collected 51 magnetotelluric (MT) and audio-magnetotelluric (AMT), stations for that research. In early 2005 we extended that research with 26 additional MT data stations, located on and near Rainier Mesa and Shoshone Mountain (RM-SM). The new stations extended the area of the hydrogeologic study previously conducted in Yucca Flat. This work was done to help refine what is known about the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal was to define the upper clastic confining unit (UCCU). The UCCU is comprised of late Devonian to Mississippian siliciclastic rocks assigned to the Eleana Formation and Chainman Shale. The UCCU underlies the Yucca Flat area and extends westward towards Shoshone Mountain, southward to Buckboard Mesa, and northward to Rainier Mesa. Late in 2005 we collected another 14 MT stations in Mid Valley and in northern Yucca Flat basin. That work was done to better determine the extent and thickness of the UCCU near the southeastern RM-SM CAU boundary with the southwestern YF CAU, and also in the northern YF CAU. The purpose of this report is to release the MT data at those 14 stations. No interpretation of the data is included here.

Open-File Report↗