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USGS2012

Laboratory studies of volcanic jets

The study of the fluid dynamics of violent volcanic eruptions by laboratory experiment is described, and the important fluid-dynamic processes that can be examined in laboratory models are discussed in detail. In preliminary experiments, pure gases are erupted from small reservoirs. The gases used are Freon 12 and Freon 22, two gases of high molecular weight and high density that are good analogs of heavy and particulate-laden volcanic gases; nitrogen, a moderate molecular weight, moderate density gas for which the thermodynamic properties are well known; and helium, a low molecular weight, lowdensity gas that is used as a basis for comparison with the behavior of the heavier gases and as an analog of steam, the gas that dominates many volcanic eruptions. Transient jets erupt from the reservoir into the laboratory upon rupture of a thin diaphragm at the exit of a convergent nozzle. The gas accelerates from rest in the reservoir to high velocity in the jet. Reservoir pressures and geometries are such that the fluid velocity in the jets is initially supersonic and later decays to subsonic. The measured reservoir pressure decreases as the fluid expands through repetitively reflecting rarefaction waves, but for the conditions of these experiments, a simple steady-discharge model is sufficient to explain the pressure decay and to predict the duration of the flow. Density variations in the flow field have been visualized with schlieren and shadowgraph photography. The observed structure of the jet is correlated with the measured pressure history. The starting vortex generated when the diaphragm ruptures becomes the head of the jet. Though the exit velocity is sonic, the flow head in the helium jet decelerates to about one-third of sonic velocity in the first few nozzle diameters, the nitrogen head decelerates to about three-fourths of sonic velocity, while Freon maintains nearly sonic velocity. The impulsive acceleration of reservoir fluid into the surrounding atmosphere produces a compression wave. The strength of this wave depends primarily on the sound speed of the fluid in the reservoir but also, secondarily with opposite effect, on the density: helium produces a relatively strong atmospheric shock while the Freons do not produce any optically observable wave front. Well-formed N waves are detected with a microphone far from the reservoir. Barrel shocks, Mach disks, and other familiar features of steady underexpanded supersonic jets form inside the jet almost immediately after passage of the flow head. These features are maintained until the pressure in the reservoir decays to sonic conditions. At low pressures the jets are relatively structureless. Gas-particle jets from volcanic eruptions may behave as pseudogases if particle concentrations and mass and momentum exchange between the components are sufficiently small. The sound speed of volcanic pseudogases can be as large as 1000 m s −1 or as small as a few tens of meters per second depending on the mass loading and initial temperature. Fluids of high sound speed produce stronger atmospheric shock waves than do those of low sound speed. Therefore eruption of a hot gas lightly laden with particulates should produce a stronger shock than eruption of a cooler or heavily laden fluid. An empirical expression suggests that the initial velocity of the head of supersonic volcanic jets is controlled by the sound speed and the ratio of the density of the erupting fluid to that of the atmosphere. The duration of gas or pseudogas eruptions is controlled by the sound speed of the fluid and the ratio of reservoir volume to vent area.

Journal of Geophysical Research Solid Earth↗

USGS1967

Water resources inventory of Connecticut Part 2: Shetucket River Basin

The Shetucket River basin has a relatively abundant supply of water of generally good quality which is derived from precipitation that has fallen on the basin. Annual precipitation has ranged from about 30 inches to 75 inches and has averaged about 45 inches over a 35-year period. Approximately 20 inches of water are returned to the atmosphere each year by evaporation and transpiration; the remainder of the annual precipitation either flows overland to streams or percolates downward to the water table and ultimately flows out of the basin in the Shetucket River or as underflow through the deposits beneath. During the autumn and winter months precipitation normally is sufficient to cause a substantial increase in the amount of water stored underground and in surface reservoirs within the basins whereas in the summer most of the precipitation is lost through evaporation and transpiration, resulting in sharply reduced streamflow and lowered groundwater levels. The mean monthly storage of water in the basin on an average is 3.5 inches higher in November than it is in June. The amount of water that flows out of the basin in the Shetucket River represents the total amount of water potentlally available for use by man. Annual runoff from the entire basin above the Quinebaug River has ranged from about 13 to 42 inches since 1929, and has averaged about 23 inches (300 billion gallons). Although runoff indicates the total amount of water potentially available, it is usually not economically or legally feasible for man to use all of it. On the other hand, with increased development, It is possible that some water will be reused several times. The water available may be tapped as it flows through the area or is temporarily stored in streams, lakes, and aquifers. The amounts that can be developed vary from place to place and time to time, depending on the amount of precipitation, on the size of drainage area, on the thickness, permeability and areal extent of aquifers, and on the variations in chemical and physical quality of the water. Differences in streamflow from point to point are due primarily to differences in the proportion of stratified drift in the drainage basin above each point, which affect the timing of streamflow, and to differences in precipitation, which affect the amount of streamflow. Information on streamflow from gaging stations may be extended to ungaged sites by accounting for both of these factors ,in calculations. Future floods on the upper Willimantic River or the Shetucket River are unlikely to cause major damage so long as buildings are not constructed below the highest flood elevations to be expected with the present system of reservoirs for flood control. Ground water can be obtained from wells almost anywhere in the Shetucket River basin, but the amount obtainable from individual wells at any particular point depends upon the type and water-bearing properties of the aquifers present. For practical purposes, the earth materials in the basin comprise three aquifers--stratified drift, till, and bedrock, Stratified drift is the only aquifer generally capable of yielding more than 100 gpm to individual wells. This aquifer covers about 18 percent of the basin and occurs chiefly In lowlands where it overlies till or bedrock. Coefficient of permeability of the coarse-grained unit of stratified drift averages about 1,900 gpd per sq ft. Drilled, screened wells tapping this unit, are known to yield from 200 to 675 gpm. Dug wells in coarse-grained stratified drift should supply at least 2 gpm per foot of drawdown over an 8-hour period. Fine-grained stratified drift has an average coefficient of permeability of about 400 gpd per sq ft and can usually yield to dug wells supplies sufficient for household use. Till and bedrock are widespread in extent but can provide only small to moderate water supplies. Till is tapped chiefly by dug wells; permanent supplies of more than 200 gpd can be obtained from dug wells at a majority of sites in areas of till, but there are many sites where the till is too impermeable or too thin to provide this much water throughout the year. The coefficient of permeability of till ranges from about 0.2 gpd per sq ft to 55 gpd per sq it. Bedrock Is tapped chiefly by drilled wells, about 90 percent of which will supply at least 3 gpm. Very few, however, will supply more than 50 gpm. The amount of ground water potentially available In an area depends upon the amount of groundwater outflow, the amount of ground water in storage, and the quantity of water available by Induced infiltration from streams and lakes. From data on permeability, saturated thickness, recharge, yield from aquifer storage, well performance, and streamflow, preliminary estimates of ground-water availability can be made for any point in the basin. Long-term yields estimated for 15 areas especially favorable for development of large ground-water supplies ranged from 1.3 to 61.8 mgd. Detailed site studies to determine optimum yields, drawdowns, and spacing of individual wells are needed before major ground-water development is undertaken In these or other areas. The chemical quality of water in the Shetucket basin Is generally good to excellent. Samples of naturally occurring surface water collected from 32 sites contained less than 61 ppm of dissolved solids and less than 32 ppm of hardness. Water from wells is more highly mineralized than naturally occurring water from streams. Even so only 7 percent of wells sampled yielded water with more than 200 ppm of dissolved sol-ids and only 9 percent yielded water with more than 120 ppm of hardness. Even in the major rivers, which are used to transport industrial waste, the dissolved mineral content is less than 100 ppm and hardness rarely exceeds 40 ppm. One notable exception occurs in the lower reaches of Little River where an exceptional amount of industrial waste is discharged into the river near Versailles. This waste is particularly noticeable during low streamflow. Iron and manganese In both ground water and surface water are the only constituents whose concentrations commonly exceed recommended limits for domestic and industrial use. Most wells in the basin yield clear water with little or no iron or manganese, but distributed among them are wells with ground water that contains enough of these dissolved constituents to be troublesome for most uses. iron concentrations in naturally occurring stream water exceeded 0.3 ppm under tow-flow conditions at 20 percent of the sites sampled. Large concentrations of iron in stream water result from discharge of iron-bearing ground water or from the discharge of water from swamps. In swamps the iron is released largely from decaying vegetation. Ground water more than 30 feet below the land surface has a relatively constant temperature, usually between 48°F and 50°F. Water temperature in very shallow wells may fluctuate from about 38°F in February or March to about 55°F in late summer. Water temperature in the larger streams fluctuates much more widely, ranging from 32°F at least for brief periods in winter, to about 85°F occasionally during The quantity of suspended sediment transported by streams in the basin is negligible, though amounts large enough to be troublesome may occur locally at times. The total amount of water used In the Shetucket Rlver basin for all purposes during 1961 was about 5,810 million gallons~ which is equivalent to 208 gpd per person, Public water systems supplied the domestic needs of nearly half the population of the basin; 10 systems were sampled, all of which provided water of better quality than the U.S. Public Health Service suggests for drinking water standards.

Connecticut↗

USGS2012

Interpretation of gravity data in a complex volcano-tectonic setting, southwestern Nevada

This regional gravity study, based on an irregular 2-km data grid, was conducted during the past few years at Yucca Mountain, southern Nye County, Nevada, as part of a program to locate a suitable repository for high-level nuclear waste. About 100 surface rock samples, three borehole gamma-gamma logs, and one borehole gravity study provide excellent density control. A nearly linear increase in density of 0.26 g/cm 3 per kilometer of depth is indicated in the thick tuff sequences that underlie the mountain. Isostatic and 2.0-g/cm 3 Bouguer corrections were applied to the observed gravity values to remove regional gradients and topographic effects, respectively. The Bare Mountain gravity high, with an isostatic anomaly maximum of 48 mGal, is connected with a greater gravity high over the Funeral Mountains, to the southwest; together, these highs result from a continuous block of dense, metamorphosed Precambrian and Paleozoic rocks that stretches across much of the Walker Lane from the east edge of Death Valley to Bare Mountain. The Calico Hills gravity high appears more likely to originate from a northeast trending buried ridge of Paleozoic rocks that extends southwestward beneath Busted Butte, 5 km southeast of the proposed repository, where two- and three-dimensional modeling indicates that the pre-Cenozoic rocks lie less than 1000 m beneath the surface. Tuff, at least 4000 m thick, fills a large steep-sided depression in the pretuff rocks beneath Yucca Mountain and Crater Flat. The gravity low and the thick tuff section lie within a large collapse area that includes the Crater Flat-Timber Mountain-Silent Canyon caldera complexes. Gravity lows in Crater Flat itself are interpreted to coincide with the source areas of the Prow Pass Member, the Bullfrog Member, and the Tram Member of the Crater Flat Tuff; these source areas add nearly 350 km 2 to the previously recognized extent of the local caldera complexes. Southward extension of the broad gravity low associated with Crater Flat into the Amargosa Desert is evidence for sector graben-type collapse segments related to the formation of the Timber Mountain caldera and superimposed on the other volcanic and extensional structures within Crater Flat.

Journal of Geophysical Research Solid Earth↗

USGS2008

EAARL coastal topography - Northern Gulf of Mexico

These remotely sensed, geographically referenced elevation measurements of Lidar-derived coastal topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. One objective of this research is to create techniques to survey areas for the purposes of geomorphic change studies following major storm events. The USGS Coastal and Marine Geology Program's National Assessment of Coastal Change Hazards project is a multi-year undertaking to identify and quantify the vulnerability of U.S. shorelines to coastal change hazards such as effects of severe storms, sea-level rise, and shoreline erosion and retreat. Airborne Lidar surveys conducted during periods of calm weather are compared to surveys collected following extreme storms in order to quantify the resulting coastal change. Other applications of high-resolution topography include habitat mapping, ecological monitoring, volumetric change detection, and event assessment. The purpose of this project is to provide highly detailed and accurate datasets of the northern Gulf of Mexico coastal areas, acquired on September 19, 2004, immediately following Hurricane Ivan. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Airborne Advanced Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532 nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking RGB (red-green-blue) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers and an integrated miniature digital inertial measurement unit which provide for sub-meter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system on September 19, 2004. The survey resulted in the acquisition of 3.2 gigabytes of data. The data were processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for pre-survey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of 'last return' elevations.

Alabama, Florida, Mississippi↗

USGS2012

Rift flank uplifts and Hinterland Basins: Comparison of the Transantarctic Mountains with the Great Escarpment of southern Africa

Uplifted rift margins are a common feature of continents and oceans. Two variants of rift flank morphologies have been recognized: One in which the topography warps down from an inland high toward the continental margin, and one where the tropographic peak lies close to the continental margin. The Great Escarpment of southern Africa and the Transantarctic Mountains are examples of the first and the second variants of rift flanks, respectively. Both rift flanks are bordered on their landward side by broad continental basins: the Kalahari and the Wilkes hinterland basins. If these basins are interpreted as flexural “outer lows” that deepen in unison with the uplift of the rift flanks, the lithosphere on the uplifted side is very rigid in both cases (elastic thickness T e of 100 ± 20 km for southern Africa and 110 ± 20 km for East Antarctica). We suggest that the variation in rift flank morphology is caused by the isostatic response to uplift forces of elastic plates sharing different boundary conditions. We model the uplift of the Transantarctic Mountains as an upward deflection of an elastic plate which is broken at the front of the Transantarctic Mountains, and we model the uplift of the Great Escarpment as an upward deflection of a continuous elastic plate that is modified by the downward load of sediments on the continental margin. Although the Transantarctic Mountain uplift is young (60–0 Ma) and the southern African uplift is old (<100 Ma), the different isostatic responses of the two margins are not a function of age, because most loading (sedimentation) and unloading (erosion) took place shortly after rifting. Detailed modeling of topography, gravity, geological markers, and the locations of depocenters suggests that lithospheric rigidity decreases under the Transantarctic Mountains, whereas in southern Africa the decrease occurs not under the Great Escarpment but far seaward under the continental shelf and slope. If the distribution of lithospheric rigidity is indicative of the thermal regime of the lithosphere, then uplifted rift flanks are not always underlain by a thermal anomaly. This and other geological evidence indicate that a single mechanism cannot explain the uplift of both the Antarctic and the African margins.

Journal of Geophysical Research B: Solid Earth↗

USGS2020

A 36-year record of rock avalanches in the Saint Elias Mountains of Alaska, with implications for future hazards

Glacial retreat and mountain-permafrost degradation resulting from rising global temperatures have the potential to impact the frequency and magnitude of landslides in glaciated environments. Several recent events, including the 2015 Taan Fiord rock avalanche, which triggered a tsunami with one of the highest wave runups ever recorded, have called attention to the hazards posed by landslides in regions like southern Alaska. In the Saint Elias Mountains, the presence of weak sedimentary and metamorphic rocks and active uplift resulting from the collision of the Yakutat and North American tectonic plates create landslide-prone conditions. To differentiate between the typical frequency of landsliding resulting from the geologic and tectonic setting of this region, and landslide processes that may be accelerated due to changes in climate, we used Landsat imagery to create an inventory of rock avalanches in a 3700 km2 area of the Saint Elias Mountains. During the period from 1984-2019, we identified 220 rock avalanches with a mean recurrence interval of 60 days. We compared our landslide inventory with a catalog of M ≥ 4 earthquakes to identify potential coseismic events, but only found three possible earthquake-triggered rock avalanches. We observed a distinct temporal cluster of 41 rock avalanches from 2013 through 2016 that correlated with above average air temperatures (including the three warmest years on record in Alaska, 2014-2016); this cluster was similar to a temporal cluster of recent rock avalanches in nearby Glacier Bay National Park and Preserve. The majority of rock avalanches initiated from bedrock ridges in probable permafrost zones, suggesting that ice loss due to permafrost degradation, as opposed to glacial thinning, could be a dominant factor contributing to rock-slope failures in the high elevation areas of the Saint Elias Mountains. Although earthquake-triggered landslides have episodically occurred in southern Alaska, evidence from our study suggests that area-normalized rates of non-coseismic rock avalanches were greater during the period from 1964 to 2019, and that the frequency of these events will continue to increase as the climate continues to warm. These findings highlight the need for hazard assessments in Alaska that address changes in landslide patterns related to climate change.

Alaska↗

USGS1998

Detrital zircon U-Pb geochronology of Cambrian to Triassic miogeoclinal and eugeoclinal strata of Sonora, Mexico

One hundred and eighty two individual detrital zircon grains from Cambrian through Permian miogeoclinal strata, Ordovician eugeoclinal rocks, and Triassic post-orogenic sediments in northwestern Sonora have been analyzed. During Cambrian, Devonian, Permian, and Triassic time, most zircons accumulating along this part of the Cordilleran margin were shed from 1.40–1.45 and 1.62–1.78 Ga igneous rocks that are widespread in the southwestern United States and northwestern Mexico. Zircons with ages of approximately 1.11 Ga are common in Cambrian strata and were apparently shed from granite bodies near the sample site. The sources of 225–280 Ma zircons in our Triassic sample are more problematic, as few igneous rocks of these ages are recognized in northwestern Mexico. Such sources may be present but unrecognized, or the grains could have been derived from igneous rocks of the appropriate ages to the northwest in the Mojave Desert region, to the east in Chihuahua and Coahuila, or to the south in accreted(?) arc-type terranes. Because the zircon grains in our Cambrian and Devonian to Triassic samples could have accumulated in proximity to basement rocks near their present position or in the Death Valley region of southern California, our data do not support or refute the existence of the Mojave-Sonora megashear. Ordovician strata of both miogeoclinal and eugeoclinal affinity are dominated by >1.77 Ga detrital zircons, which are considerably older than most basement rocks in the region. Zircon grains in the miogeoclinal sample were apparently derived from the Peace River arch area of northwestern Canada and transported southward by longshore currents. The eugeoclinal grains may also have come from the Peace River arch region, with southward transport by either sedimentary or tectonic processes, or they may have been shed from off-shelf slivers of continents (perhaps Antarctica?) removed from the Cordilleran margin during Neoproterozoic rifting. It is also possible that the Ordovician eugeoclinal strata are far traveled and exotic to North America.

Journal of Geophysical Research B: Solid Earth↗

USGS1999

Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula

Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the M w = 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ∼470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post-1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate “fault-normal” compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (∼10°) through the southernmost peninsula. A zone of seismic quiescence ∼15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slip-faulting focal mechanisms (including a M L = 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudogravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ∼3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San Andreas right stepover region and at least 15 km along-strike both to the SE and NW. The 1906 San Francisco earthquake may have nucleated within the San Andreas right stepover, which may help explain the bilateral nature of rupture of this event. Our analysis suggests two seismic hazards for the San Francisco Peninsula in addition to the hazard associated with a M = 7 to 8 strike-slip earthquake along the San Andreas fault: the potential for a M ≈ 6 normal-faulting earthquake just 5–8 km west of San Francisco and a M = 6+ thrust faulting event in the southern peninsula.

Journal of Geophysical Research B: Solid Earth↗

USGS2018

Strain partitioning in southeastern Alaska: Is the Chatham Strait Fault active?

A 1200 km-long transform plate boundary passes through southeastern Alaska and northwestern British Columbia and represents one of the most seismically active, but poorly understood continental margins of North America. Although most of the plate motion is accommodated by the right-lateral Queen Charlotte–Fairweather Fault (QCFF) System, which has produced at least six M > 7 earthquakes since 1920, seismic hazard ass essments also include the Chatham Strait Fault (CSF) as a potentially active, 400 km-long strike slip fault that cuts northward through southeastern Alaska, connecting with the Eastern Denali Fault. Nearly the entire length of the CSF is submerged beneath Chatham Strait and Lynn Canal and has never been systematically imaged using high-resolution marine geophysical approaches. In this study we present an integrated analysis of new marine seismic reflectiondata ac quired across Lynn Canal and tectonic block modeling constrained by data from continuous and campaign GPS sites. Seismic profiles cross the CSF at twelve locations spanning ∼50 km of fault length; they reveal thick (up to 300 m) packages of glaciomarine sedimentary facies emplaced on an unconformity su rface that formed during the Last Glacial Maximum (LGM). Localized warping of post-LGM stratigraphy (∼13.9 kyr B.P. to present) appears to correlate with sediment drape on basement topography and current-controlled deposition. There is no evidence for an active fault along the axis of Lynn Canal in the seismic reflection data. Crustal block models constrained by GPS data allow, but do not require, a maximum slip rate o f 2–3 mm/yr along the CSF; higher slip rates on the CSF result in significant misfit to GPS data in the surrounding region. Based on the combined marine geophysical and GPS observations, it is plausible that the CSF has not generated resolvable coseismic deformation in the last ∼13 ka and that the modern slip-rate is <1 mm/yr. We propose that models for strain transfer between the QCFF and the Denali Fault, and seismic hazard maps in general, may need to be reevaluated.

Alaska↗

USGS2024

Twenty years of explosive-effusive activity at El Reventador volcano (Ecuador) recorded in its geomorphology

Shifts in activity at long-active, open-vent volcanoes are difficult to forecast because precursory signals are enigmatic and can be lost in and amongst daily activity. Here, we propose that crater and vent morphologies, along with summit height, can help us bring some insights into future activity at one of Ecuador’s most active volcanoes El Reventador. On 3 November 2002, El Reventador volcano experienced the largest eruption in Ecuador in the last 140 years and has been continuously active ever since with transitions between and coexistence of explosive and effusive activity, characterized by Strombolian and Vulcanian behavior. Based on the analysis of a large dataset of thermal and visual images, we determined that in the last 20 years of activity, the volcano faced three destructive events: A. Destruction of the upper part of the summit leaving a north-south breached crater (3 November 2002), B. NE border crater collapse (2017), and C. NW flank collapse (2018), with two periods of reconstruction of the edifice: Period 1. Refill of the crater (2002-early 2018) and Period 2. Refill of the 2018 scar (April 2018–December 2022). Through photogrammetric analysis of visual and thermal images acquired in 11 overflights of the volcano, we created a time-series of digital elevation models (DEMs) to determine the maximum height of the volcano at each date, quantify the volume changes between successive dates, and characterize the morphological changes in the summit region. We estimate that approximately 34.1x10 6 m 3 of volcanic material was removed from the volcano due to destructive events, whereas 64.1x10 6 m 3 was added by constructive processes. The pre-2002 summit height was 3,560 m and due to the 2002 eruption it decreased to 3,527 m; it regained its previous height between 2014 and 2015 and the summit crater was completely filled by early April 2018. Event A resulted from an intrusion of magma that erupted violently; we proposed that Events B and C could be a result of an intrusion as well but may also be due to a lack of stability of the volcano summit which occurs when it reaches its maximum height of approximately 3,590 and 3,600 m.

El Reventador↗

USGS2012

Remagnetization of the Coast Range Ophiolite and Lower Part of the Great Valley Sequence in Northern California and Southwest Oregon

Overprinted magnetizations have been found at four localities in the Middle Jurassic Coast Range ophiolite and the overlying Upper Jurassic and Lower Cretaceous Great Valley sequence in northern California and at one locality in the partially correlative Lower Cretaceous Days Creek Formation in southwest Oregon. At Del Puerto Canyon, on the east side of the Diablo Range, a pilot study of the upper Jurassic Lotta Creek Formation gives in situ paleomagnetic directions grouped around the present geomagnetic field, suggesting magnetic overprinting long after deposition and folding. We suggest that the loss of original magnetization could be the result of long burial at about 7 km depth, followed by Late Tertiary uplift; the possibility of chemical remagnetization, however, can not be excluded. Paleomagnetic data from sandstones from the Lower Cretaceous Great Valley sequence in the Wilbur Springs area suggest Cenozoic remagnetization that could be related to Pliocene and Pleistocene volcanic and hydrothermal activity in the area. The results from calcareous concretions in the Wilbur Springs area, from 21 sites from basalts and overlying sedimentary rocks of the Great Valley sequence at Stonyford, and from several sites in various rock types in the Coast Range ophiolite and Great Valley sequence near Paskenta suggest unblocking of magnetization during the long period of burial at depth of 7 km or more and remagnetization during tectonic uplift in the Late Cretaceous or Tertiary. Chemical remagnetization, however, can not be excluded. The paleomagnetic data from six sites in Lower Cretaceous sedimentary rocks of the Days Creek Formation in southwest Oregon, which overlies a dismembered ophiolite, fail the fold test. In situ paleomagnetic directions group near the expected Tertiary field directions. These sedimentary rocks may have been remagnetized during a major Eocene tectonic event known to have occurred in this region. The paleomagnetic results confirm that the Coast Range ophiolite and the seemingly little-deformed Great Valley sequence in northern California, as well as correlative rocks in southwest Oregon have had a complex tectonic history. Once the nature and timing of these events are better understood, the timing of remagnetization may be further constrained, which, in turn, could give further insight into the nature of the tectonic events

California, Oregon↗

USGS2022

Forecasting explosions at Sinabung Volcano, Indonesia, based on SO2 emission rates

Dome-building volcanic eruptions are often associated with frequent Vulcanian explosions, which constitute a substantial threat to proximal communities. One proposed mechanism driving such explosions is the sealing of the shallow volcanic system followed by pressurization due to gas accumulation beneath the seal. We investigate this hypothesis at Sinabung Volcano (Sumatra, Indonesia), which has been in a state of eruption since August 2010. In 2013, the volcano began erupting a lava dome and lava flow, and frequent explosions produced eruptive columns that rose many kilometers into the atmosphere and at times sent pyroclastic density currents down the southeast flanks. A network of scanning Differential Optical Absorption Spectrometers (DOAS) was installed on the volcano’s eastern flank in 2016 to continuously monitor SO 2 emission rates during daytime hours. Analysis of the DOAS data from October 2016 to September 2017 revealed that passive SO 2 emissions were generally lower in the 5 days leading up to explosive events (∼100 t/d) than was common in 5-day periods leading up to days on which no explosions occurred (∼200 t/d). The variability of passive SO 2 emissions, expressed as the standard deviation, also took on a slightly wider range of values before days with explosions (0–103 t/d at 1-sigma) than before days without explosions (43–117 t/d). These observations are consistent with the aforementioned seal-failure model, where the sealing of the volcanic conduit blocks gas emissions and leads to pressurization and potential Vulcanian explosions. We develop a forecasting methodology that allows calculation of a relative daily explosion probability based solely on measurements of the SO 2 emission rate in the preceding days. We then calculate forecast explosion probabilities for the remaining SO 2 emissions dataset (October 2017—September 2021). While the absolute accuracy of forecast explosion probabilities is variable, the method can inform the probability of an explosion occurring relative to that on other days in each test period. This information can be used operationally by volcano observatories to assess relative risk. The SO 2 emissions-based forecasting method is likely applicable to other open vent volcanoes experiencing dome-forming eruptions.

Frontiers in Earth Science↗

USGS2015

Mineral resource of the month: silver

Silver, one of the eight precious or noble metals, has been used extensively throughout recorded history for various medical purposes, ornaments and utensils, and for its intrinsic value as the basis for trade and monetary systems. Silver has played a significant role in world history, financing a Greek victory over the Persians in 480 B.C., helping Spain become a world power in the 16th and 17th centuries, and helping fund the Union forces during the U.S. Civil War, to give a few examples. Silver occurs as a native metal; in sulfide ores of copper, lead and zinc; and sometimes with bismuth and antimony. Silver is always present in ores containing gold. The Silver Institute estimated that, in 2013, about 29 percent of global mined silver came from silver ores, 38 percent came from lead-zinc ores, 20 percent came from copper ores and 13 percent came from gold ores. Silver's properties include its ability to endure extreme temperatures, its high reflectance of light, its thermal and electrical conductivity (the highest of all metals), and its strength, malleability and ductility. Demand for silver arises from three areas: industrial applications (in electronics, brazing alloys and solders, photography and other uses), investment (including coins and bars), and silver jewelry and decor (including silverware). Silver-halide X-rays were long the standard, but are now being replaced by digital imaging technology. Since 2000, demand for silver in photographic applications has also declined owing to the use of digital photography. In 2013, uses in electronics accounted for 42 percent of U.S. silver consumption; coins and metals for 35 percent; photography for 13 percent; jewelry and silverware for 7 percent; and other uses for 3 percent. Silver is also used in solar power generation: 90 percent of crystalline silicon photovoltaic solar cells use silver paste. On windows, a transparent layer of silver reflects up to 95 percent of sunlight, saving energy. In water purification, use of silver eliminates the need for corrosive chlorine. For more information on silver and other mineral resources, visit: http://minerals.usgs.gov/minerals .

Earth↗

USGS2014

Evaluation of statistically downscaled GCM output as input for hydrological and stream temperature simulation in the Apalachicola–Chattahoochee–Flint River Basin (1961–99)

The accuracy of statistically downscaled general circulation model (GCM) simulations of daily surface climate for historical conditions (1961–99) and the implications when they are used to drive hydrologic and stream temperature models were assessed for the Apalachicola–Chattahoochee–Flint River basin (ACFB). The ACFB is a 50 000 km 2 basin located in the southeastern United States. Three GCMs were statistically downscaled, using an asynchronous regional regression model (ARRM), to ⅛° grids of daily precipitation and minimum and maximum air temperature. These ARRM-based climate datasets were used as input to the Precipitation-Runoff Modeling System (PRMS), a deterministic, distributed-parameter, physical-process watershed model used to simulate and evaluate the effects of various combinations of climate and land use on watershed response. The ACFB was divided into 258 hydrologic response units (HRUs) in which the components of flow (groundwater, subsurface, and surface) are computed in response to climate, land surface, and subsurface characteristics of the basin. Daily simulations of flow components from PRMS were used with the climate to simulate in-stream water temperatures using the Stream Network Temperature (SNTemp) model, a mechanistic, one-dimensional heat transport model for branched stream networks. The climate, hydrology, and stream temperature for historical conditions were evaluated by comparing model outputs produced from historical climate forcings developed from gridded station data (GSD) versus those produced from the three statistically downscaled GCMs using the ARRM methodology. The PRMS and SNTemp models were forced with the GSD and the outputs produced were treated as “truth.” This allowed for a spatial comparison by HRU of the GSD-based output with ARRM-based output. Distributional similarities between GSD- and ARRM-based model outputs were compared using the two-sample Kolmogorov–Smirnov (KS) test in combination with descriptive metrics such as the mean and variance and an evaluation of rare and sustained events. In general, precipitation and streamflow quantities were negatively biased in the downscaled GCM outputs, and results indicate that the downscaled GCM simulations consistently underestimate the largest precipitation events relative to the GSD. The KS test results indicate that ARRM-based air temperatures are similar to GSD at the daily time step for the majority of the ACFB, with perhaps subweekly averaging for stream temperature. Depending on GCM and spatial location, ARRM-based precipitation and streamflow requires averaging of up to 30 days to become similar to the GSD-based output. Evaluation of the model skill for historical conditions suggests some guidelines for use of future projections; while it seems correct to place greater confidence in evaluation metrics which perform well historically, this does not necessarily mean those metrics will accurately reflect model outputs for future climatic conditions. Results from this study indicate no “best” overall model, but the breadth of analysis can be used to give the product users an indication of the applicability of the results to address their particular problem. Since results for historical conditions indicate that model outputs can have significant biases associated with them, the range in future projections examined in terms of change relative to historical conditions for each individual GCM may be more appropriate.

Florida, Georgia↗

USGS2009

Cenozoic stratigraphy of the Sahara, Northern Africa

This paper presents an overview of the Cenozoic stratigraphic record in the Sahara, and shows that the strata display some remarkably similar characteristics across much of the region. In fact, some lithologies of certain ages are exceptionally widespread and persistent, and many of the changes from one lithology to another appear to have been relatively synchronous across the Sahara. The general stratigraphic succession is that of a transition from early Cenozoic carbonate strata to late Cenozoic siliciclastic strata. This transition in lithology coincides with a long-term eustatic fall in sea level since the middle Cretaceous and with a global climate transition from a Late Cretaceous–Early Eocene “warm mode” to a Late Eocene–Quaternary “cool mode”. Much of the shorter-term stratigraphic variability in the Sahara (and even the regional unconformities) also can be correlated with specific changes in sea level, climate, and tectonic activity during the Cenozoic. Specifically, Paleocene and Eocene carbonate strata and phosphate are suggestive of a warm and humid climate, whereas latest Eocene evaporitic strata (and an end-Eocene regional unconformity) are correlated with a eustatic fall in sea level, the build-up of ice in Antarctica, and the appearance of relatively arid climates in the Sahara. The absence of Oligocene strata throughout much of the Sahara is attributed to the effects of generally low eustatic sea level during the Oligocene and tectonic uplift in certain areas during the Late Eocene and Oligocene. Miocene sandstone and conglomerate are attributed to the effects of continued tectonic uplift around the Sahara, generally low eustatic sea level, and enough rainfall to support the development of extensive fluvial systems. Middle–Upper Miocene carbonate strata accumulated in northern Libya in response to a eustatic rise in sea level, whereas Upper Miocene mudstone accumulated along the south side of the Atlas Mountains because uplift of the mountains blocked fluvial access to the Mediterranean Sea. Uppermost Miocene evaporites (and an end-Miocene regional unconformity) in the northern Sahara are correlated with the Messinian desiccation of the Mediterranean Sea. Abundant and widespread Pliocene paleosols are attributed to the onset of relatively arid climate conditions and (or) greater variability of climate conditions, and the appearance of persistent and widespread eolian sediments in the Sahara is coincident with the major glaciation in the northern hemisphere during the Pliocene.

Journal of African Earth Sciences↗

USGS2015

Two magma bodies beneath the summit of Kilauea Volcano unveiled by isotopically distinct melt deliveries from the mantle

The summit magma storage reservoir of Kīlauea Volcano is one of the most important components of the magmatic plumbing system of this frequently active basaltic shield-building volcano. Here we use new high-precision Pb isotopic analyses of Kīlauea summit lavas—from 1959 to the active Halema‘uma‘u lava lake—to infer the number, size, and interconnectedness of magma bodies within the volcano's summit reservoir. From 1971 to 1982, the 206 Pb/ 204 Pb ratios of the lavas define two separate magma mixing trends that correlate with differences in vent location and/or pre-eruptive magma temperature. These relationships, which contrast with a single magma mixing trend for lavas from 1959 to 1968, indicate that Kīlauea summit eruptions since at least 1971 were supplied from two distinct magma bodies. The locations of these magma bodies are inferred to coincide with two major deformation centers identified by geodetic monitoring of the volcano's summit region: (1) the main locus of the summit reservoir &sim;2–4 km below the southern rim of Kīlauea Caldera and (2) a shallower magma body <2 km below the eastern rim of Halema‘uma‘u pit crater. Residence time modeling suggests that the total volume of magma within Kīlauea's summit reservoir during the late 20th century (1959–1982) was exceedingly small (&sim;0.1–0.5 km 3 ). Voluminous Kīlauea eruptions, such as the ongoing, 32-yr old Pu‘u ‘Ō‘ō rift eruption (>4 km 3 of lava erupted), must therefore be sustained by a nearly continuous supply of new melt from the mantle. The model results show that a minimum of four compositionally distinct, mantle-derived magma batches were delivered to the volcano (at least three directly to the summit reservoir) since 1959. These melt inputs correlate with the initiation of energetic (1959 Kīlauea Iki) and/or sustained (1969–1974 Mauna Ulu, 1983-present Pu‘u ‘Ō‘ō and 2008-present Halema‘uma‘u) eruptions. Thus, Kīlauea's eruptive behavior is partly tied to the delivery of new magma batches from the volcano's source region within the Hawaiian mantle plume.

Hawaii↗

USGS2014

Growth and degradation of Hawaiian volcanoes

The 19 known shield volcanoes of the main Hawaiian Islands—15 now emergent, 3 submerged, and 1 newly born and still submarine—lie at the southeast end of a long-lived hot spot chain. As the Pacific Plate of the Earth’s lithosphere moves slowly northwestward over the Hawaiian hot spot, volcanoes are successively born above it, evolve as they drift away from it, and eventually die and subside beneath the ocean surface. The massive outpouring of lava flows from Hawaiian volcanoes weighs upon the oceanic crust, depressing it by as much as 5 km along an axial Hawaiian Moat. The periphery of subsidence is marked by the surrounding Hawaiian Arch. Subsidence is ongoing throughout almost all of a volcano’s life. During its active life, an idealized Hawaiian volcano passes through four eruptive stages: preshield, shield, postshield, and rejuvenated. Though imperfectly named, these stages match our understanding of the growth history and compositional variation of the Hawaiian volcanoes; the stages reflect variations in the amount and rate of heat supplied to the lithosphere as it overrides the hot spot. Principal growth occurs in the first 1–2 million years as each volcano rises from the sea floor or submarine flank of an adjacent volcano. Volcanic extinction ensues as a volcano moves away from the hot spot. Eruptive-stage boundaries are drawn somewhat arbitrarily because of their transitional nature. Preshield-stage lava is alkalic as a consequence of a nascent magma-transport system and less extensive melting at the periphery of the mantle plume fed by the hot spot. The shield stage is the most productive volcanically, and each Hawaiian volcano erupts an estimated 80–95 percent of its ultimate volume in tholeiitic lavas during this stage. Shield-stage volcanism marks the time when a volcano is near or above the hot spot and its magma supply system is robust. This most active stage may also be the peak time when giant landslides modify the flanks of the volcanoes, although such processes begin earlier and extend later in the life of the volcanoes. Late-shield strata extend the silica range as alkali basalt and even hawaiite lava flows are sparsely interlayered with tholeiite at some volcanoes. Rare are more highly fractionated shield-stage lava flows, which may reach 68 weight percent SiO 2 . Intervolcano compositional differences result mainly from variations in the part of the mantle plume sampled by magmatism and the distribution of magma sources within it. Volcanism wanes gradually as Hawaiian volcanoes move away from the hot spot, passing from the shield stage into the postshield stage. Shallow magma reservoirs (1–7-km depth) of the shield-stage volcanoes cannot be sustained as magma supply lessens, but smaller reservoirs at 20–30-km depth persist. The rate of extrusion diminishes by a factor of 10 late in the shield stage, and the composition of erupted lava becomes more alkalic—albeit erratically—as the degree of melting diminishes. The variation makes this transition, from late shield to postshield, difficult to define rigorously. Of the volcanoes old enough to have seen this transition, eight have postshield strata sufficiently distinct and widespread to map separately. Only two, Ko‘olau and Lāna‘i, lack rocks of postshield composition. Five Hawaiian volcanoes have seen rejuvenated-stage volcanism following quiescent periods that ranged from 2.0 to less than 0.5 million years. The rejuvenated stage can be brief—only one or two eruptive episodes—or notably durable. That on Ni‘ihau lasted from 2.2 to 0.4 million years ago; on Kaua‘i, the stage has been ongoing since 3.5 million years ago. As transitions go, the rejuvenated stage may be thought of as the long tail of alkalic volcanism that begins in late-shield time and persists through the postshield (+rejuvenated-stage) era. Because successive Hawaiian volcanoes erupt over long and overlapping spans of time, there is a wide range in the age of volcanism along the island chain, even though the age of Hawaiian shields is progressively younger to the southeast. For example, almost every island from Ni‘ihau to Hawai‘i had an eruption in the time between 0.3 and 0.4 million years ago, even though only the Island of Hawai‘i had active volcanoes in their shield stage during that time. Once they have formed, Hawaiian volcanoes become subject to a spectrum of processes of degradation. Primary among these are subaerial erosion, landslides, and subsidence. The islands, especially those that grow high above sea level, experience mean annual precipitation that locally exceeds 9 m, leading to rapid erosion that can carve deep canyons in less than 1 million years. Hawaiian volcanoes have also been modified by giant landslides. Seventeen discrete slides that formed in the past 5 m.y. have been identified around the main Hawaiian Islands, and fully 70 are known along the Hawaiian Ridge between Midway Islands and the Island of Hawai‘i. These giant landslides displace large amounts of seawater to generate catastrophic giant waves (megatsunami). The geologic evidence for megatsunami in the Hawaiian Islands includes chaotic coral and lava-clast breccia preserved as high as 155 m above sea level on Lāna‘i and Moloka‘i. Large Hawaiian volcanoes can persist as islands through the rapid subsidence by building upward rapidly enough. But in the long run, subsidence, coupled with surface erosion, erases any volcanic remnant above sea level in about 15 m.y. One consequence of subsidence, in concert with eustatic changes in sea level, is the drowning of coral reefs that drape the submarine flanks of the actively subsiding volcanoes. At least six reefs northwest of the Island of Hawai‘i form a stairstep configuration, the oldest being deepest.

Hawaii↗

USGS1998

Earthquake triggering by transient and static deformations

Observational evidence for both static and transient near-field and far-field triggered seismicity are explained in terms of a frictional instability model, based on a single degree of freedom spring-slider system and rate- and state-dependent frictional constitutive equations. In this study a triggered earthquake is one whose failure time has been advanced by Δ t (clock advance) due to a stress perturbation. Triggering stress perturbations considered include square-wave transients and step functions, analogous to seismic waves and coseismic static stress changes, respectively. Perturbations are superimposed on a constant background stressing rate which represents the tectonic stressing rate. The normal stress is assumed to be constant. Approximate, closed-form solutions of the rate-and-state equations are derived for these triggering and background loads, building on the work of Dieterich [1992, 1994]. These solutions can be used to simulate the effects of static and transient stresses as a function of amplitude, onset time t 0 , and in the case of square waves, duration. The accuracies of the approximate closed-form solutions are also evaluated with respect to the full numerical solution and t 0 . The approximate solutions underpredict the full solutions, although the difference decreases as t 0 approaches the end of the earthquake cycle. The relationship between Δ t and t 0 differs for transient and static loads: a static stress step imposed late in the cycle causes less clock advance than an equal step imposed earlier, whereas a later applied transient causes greater clock advance than an equal one imposed earlier. For equal Δ t , transient amplitudes must be greater than static loads by factors of several tens to hundreds depending on t 0 . We show that the rate-and-state model requires that the total slip at failure is a constant, regardless of the loading history. Thus a static load applied early in the cycle, or a transient applied at any time, reduces the stress at the initiation of failure, whereas static loads that are applied sufficiently late raise it. Rate-and-state friction predictions differ markedly from those based on Coulomb failure stress changes (ΔCFS) in which Δ t equals the amplitude of the static stress change divided by the background stressing rate. The ΔCFS model assumes a stress failure threshold, while the rate-and-state equations require a slip failure threshold. The complete rate-and-state equations predict larger Δ t than the ΔCFS model does for static stress steps at small t 0 , and smaller Δ t than the ΔCFS model for stress steps at large t 0 . The ΔCFS model predicts nonzero Δ t only for transient loads that raise the stress to failure stress levels during the transient. In contrast, the rate-and-state model predicts nonzero Δ t for smaller loads, and triggered failure may occur well after the transient is finished. We consider heuristically the effects of triggering on a population of faults, as these effects might be evident in seismicity data. Triggering is manifest as an initial increase in seismicity rate that may be followed by a quiescence or by a return to the background rate. Available seismicity data are insufficient to discriminate whether triggered earthquakes are “new” or clock advanced. However, if triggering indeed results from advancing the failure time of inevitable earthquakes, then our modeling suggests that a quiescence always follows transient triggering and that the duration of increased seismicity also cannot exceed the duration of a triggering transient load. Quiescence follows static triggering only if the population of available faults is finite.

Journal of Geophysical Research B: Solid Earth↗