Geology topics

Daniel Dzurisin

Publications and source records attributed to Daniel Dzurisin.

At least 37 records · Page 2Linked to original sources

USGS2012

Evidence from gravity data for an intrusive complex beneath Mount St. Helens

On the basis of gravity data, aided by aeromagnetic, magnetotelluric, side-looking radar, and geologic information, we tentatively identify a large, shallow intrusive complex beneath Mount St. Helens. The complex is roughly 5–6 km thick and has apparently intruded a buried and compressed Mesozoic forearc sedimentary sequence. The lateral extent of the intrusive complex is uncertain, and we give three alternative models varying from about 18 by 10 km to as much as 18 by 22 km. The western boundary of the inferred Mount St. Helens intrusion abuts several of a number of Tertiary and younger plutons that crop out in the area. The Mount St. Helens intrusion apparently is adjacent to sedimentary rock or shallow volcanic rock along most of the remainder of its boundary. A ringlike drainage pattern around Mount St. Helens suggests subsidence caused by removing magma from deep beneath Mount St. Helens and adding this mass to the Mount St. Helens edifice and its underlying intrusion. Our analysis indicates that the average bulk density of the volcanic rock comprising Mount St. Helens is about 2.15 g/cm 3 .

Washington↗

USGS2012

Digital elevation model generation from satellite interferometric synthetic aperture radar: Chapter 5

An accurate digital elevation model (DEM) is a critical data set for characterizing the natural landscape, monitoring natural hazards, and georeferencing satellite imagery. The ideal interferometric synthetic aperture radar (InSAR) configuration for DEM production is a single-pass two-antenna system. Repeat-pass single-antenna satellite InSAR imagery, however, also can be used to produce useful DEMs. DEM generation from InSAR is advantageous in remote areas where the photogrammetric approach to DEM generation is hindered by inclement weather conditions. There are many sources of errors in DEM generation from repeat-pass InSAR imagery, for example, inaccurate determination of the InSAR baseline, atmospheric delay anomalies, and possible surface deformation because of tectonic, volcanic, or other sources during the time interval spanned by the images. This chapter presents practical solutions to identify and remove various artifacts in repeat-pass satellite InSAR images to generate a high-quality DEM.

Book chapter↗

USGS2012

History of surface displacements at the Yellowstone Caldera, Wyoming, from leveling surveys and InSAR observations, 1923-2008

Modern geodetic studies of the Yellowstone caldera, Wyoming, and its extraordinary tectonic, magmatic, and hydrothermal systems date from an initial leveling survey done throughout Yellowstone National Park in 1923 by the U.S. Coast and Geodetic Survey. A repeat park-wide survey by the U.S. Geological Survey (USGS) and the University of Utah during 1975-77 revealed that the central part of the caldera floor had risen more than 700 mm since 1923, at an average rate of 14±1 mm/yr. From 1983 to 2007, the USGS conducted 15 smaller surveys of a single level line that crosses the northeast part of the caldera, including the area where the greatest uplift had occurred from 1923 to 1975-77. The 1983 and 1984 surveys showed that uplift had continued at an average rate of 22±1 mm/yr since 1975-77, but no additional uplift occurred during 1984-85 (-2±5 mm/yr), and during 1985-95 the area subsided at an average rate of 19±1 mm/yr. The change from uplift to subsidence was accompanied by an earthquake swarm, the largest ever recorded in the Yellowstone area (as of March 2012), starting in October 1985 and located near the northwest rim of the caldera. Interferometric synthetic aperture radar (InSAR) images showed that the area of greatest subsidence migrated from the northeast part of the caldera (including the Sour Creek resurgent dome) during 1992-93 to the southwest part (including the Mallard Lake resurgent dome) during 1993-95. Thereafter, uplift resumed in the northeast part of the caldera during 1995-96, while subsidence continued in the southwest part. The onset of uplift migrated southwestward, and by mid-1997, uplift was occurring throughout the entire caldera (essentially rim to rim, including both domes). Consistent with these InSAR observations, leveling surveys indicated 24±3 mm of uplift in the northeast part of the caldera during 1995-98. The beginning of uplift was coincident with or followed shortly after an earthquake swarm near the north caldera rim during June-July 1995 - the strongest swarm since 1985. Rather than a single deformation source as inferred from leveling surveys, the InSAR images revealed two distinct sources - one beneath each resurgent dome on the caldera floor. Subsequently, repeated GPS surveys (sometimes referred to as "campaign" surveys to distinguish them from continuous GPS observations) and InSAR images revealed a third deformation source beneath the north caldera rim. The north-rim source started to inflate in or about 1995, resulting in as much as 80 mm of surface uplift by 2000. Meanwhile, motion of the caldera floor changed from uplift to subsidence during 1997-8. The north rim area rose, while the entire caldera floor (including both domes) subsided until 2002, when both motions paused. Uplift in the northeast part of the caldera resumed in mid-2004 at a historically unprecedented rate of as much as 70 mm/yr, while the north rim area subsided at a lesser rate. Resurveys of the level line across the northeast part of the caldera in 2005 and 2007 indicated the greatest average uplift rate since the initial survey in 1923-53±3 mm/yr. Data from a nearby continuous GPS (CGPS) station showed that the uplift rate slowed to 40-50 mm/yr during 2007-8 and to near zero by September 2009. Following an intense earthquake swarm during January-February 2010, this one near the northwest caldera rim and the strongest since the 1985 swarm in the same general area, CGPS stations recorded the onset of subsidence throughout the entire caldera. Any viable model for the cause(s) of ground deformation at Yellowstone should account for (1) three distinct deformation sources and their association with both resurgent domes and the north caldera rim; (2) interplay among these sources, as suggested by the timing of major changes in deformation mode; (3) migration of the area of greatest subsidence or uplift from the northeast part of the caldera to the southwest part during 1992-95 and 1995-97, respectively; (4) repeated cycles of uplift and subsidence and sudden changes from uplift to subsidence or vice versa; (5) spatial and temporal relationships between changes in deformation mode and strong earthquake swarms; and (6) lateral dimensions of all three deforming areas that indicate source depths in the range of 5 to 15 km. We prefer a conceptual model in which surface displacements at Yellowstone are caused primarily by variations in the flux of basaltic magma into the crust beneath the caldera. Specifically, we envision a magmatic conduit system beneath the northeast part of the caldera that supplies basalt from a mantle source to an accumulation zone at 5-10 km depth, perhaps at a rheological boundary within a crystallizing rhyolite body remnant from past eruptions. Increases in the magma flux favor uplift of the caldera and decreases favor subsidence. A delicate equilibrium exists among the mass and heat flux from basaltic intrusions, heat and volatile loss from the crystallizing rhyolite body, and the overlying hydrothermal system. In the absence of basalt input, steady subsidence occurs mainly as a result of fluid loss from crystallizing rhyolite. At times when a self-sealing zone in the deep hydrothermal system prevents the escape of magmatic fluid, the resulting pressure increase contributes to surface uplift within the caldera; such episodes end when the seal ruptures during an earthquake swarm. To account for the north rim deformation source, we propose that magma or fluid exsolved from magma episodically escapes the caldera system at the three-way structural intersection of (1) the northern caldera boundary, (2) an active seismic belt to the north-northwest that is associated with the Hebgen Lake fault zone, and (3) the Norris - Mammoth corridor - a zone of faults, volcanic vents, and thermal activity that strikes north from the north rim of the caldera near Norris Geyser Basin to Mammoth Hot Springs near the northern boundary of Yellowstone National Park. Increased fluid flux out of the caldera by way of this intersection favors subsidence of the north rim area, and decreased flux favors uplift. This model does not account for poroelastic and thermoelastic effects, nonelastic rheology, or heat and mass transport in the hot and wet subcaldera crust. Such effects almost surely play a role in caldera deformation and are an important topic of ongoing research.

Wyoming↗

USGS2011

Rapid, low-cost photogrammetry to monitor volcanic eruptions: An example from Mount St. Helens, Washington, USA

We describe a low-cost application of digital photogrammetry using commercially available photogrammetric software and oblique photographs taken with an off-the-shelf digital camera to create sequential digital elevation models (DEMs) of a lava dome that grew during the 2004–2008 eruption of Mount St. Helens (MSH) volcano. Renewed activity at MSH provided an opportunity to devise and test this method, because it could be validated against other observations of this well-monitored volcano. The datasets consist of oblique aerial photographs (snapshots) taken from a helicopter using a digital single-lens reflex camera. Twelve sets of overlapping digital images of the dome taken during 2004–2007 were used to produce DEMs and to calculate lava dome volumes and extrusion rates. Analyses of the digital images were carried out using photogrammetric software to produce three-dimensional coordinates of points identified in multiple photos. The evolving morphology of the dome was modeled by comparing successive DEMs. Results were validated by comparison to volume measurements derived from traditional vertical photogrammetric surveys by the US Geological Survey Cascades Volcano Observatory. Our technique was significantly less expensive and required less time than traditional vertical photogrammetric techniques; yet, it consistently yielded volume estimates within 5% of the traditional method. This technique provides an inexpensive, rapid assessment tool for tracking lava dome growth or other topographic changes at restless volcanoes.

Washington↗

USGS2011

EarthScoping the inner workings of magmatic systems

In the shadow of one of the world's great volcanic systems, an intensive 3-day workshop was undertaken to work toward developing a scientific plan for the magmatic systems component of the U.S. National Science Foundation's (NSF) EarthScope Initiative. This NSF-sponsored workshop was designed to provide direction to the EarthScope planning committee and the NSF in developing scientific, technical, deployment, and management decisions related to the magmatic systems component of EarthScope. The meeting featured a mixture of oral and poster scientific sessions, breakout group and plenary discussions, and a field trip to examine one of the targets of the EarthScope magmatic science research plan: Mount St. Helens. The 60 participants represented a broad cross-section of the volcanology community including geologists, geophysicists, geodesists, penologists, and geochemists. Details on the meeting plan can be viewed at http://www. unavco.net/earthscope.asp.

Eos Science News↗

USGS2011

Volcano deformation and gravity workshop synopsis and outcomes: The 2008 volcano deformation and temporal gravity change workshop

A volcano workshop was held in Washington State, near the U.S. Geological Survey (USGS) Cascades Volcano Observatory. The workshop, hosted by the USGS Volcano Hazards Program (VHP), included more than 40 participants from the United States, the European Union, and Canada. Goals were to promote (1) collaboration among scientists working on active volcanoes and (2) development of new tools for studying volcano deformation. The workshop focused on conventional and emerging techniques, including the Global Positioning System (GPS), borehole strain, interferometric synthetic aperture radar (InSAR), gravity, and electromagnetic imaging, and on the roles of aqueous and magmatic fluids.

Eos, Transactions, American Geophysical Union↗

USGS2010

Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 1. Intereruption deformation, 1997–2008

Starting soon after the 1997 eruption at Okmok volcano and continuing until the start of the 2008 eruption, magma accumulated in a storage zone centered ~3.5 km beneath the caldera floor at a rate that varied with time. A Mogi-type point pressure source or finite sphere with a radius of 1 km provides an adequate fit to the deformation field portrayed in time-sequential interferometric synthetic aperture radar images. From the end of the 1997 eruption through summer 2004, magma storage increased by 3.2–4.5 × 10 7 m 3 , which corresponds to 75–85% of the magma volume erupted in 1997. Thereafter, the average magma supply rate decreased such that by 10 July 2008, 2 days before the start of the 2008 eruption, magma storage had increased by 3.7–5.2 × 10 7 m 3 or 85–100% of the 1997 eruption volume. We propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region. Eventually the effects of continuing magma supply and vesiculation of stored magma caused a critical pressure threshold to be exceeded, triggering the 2008 eruption. A similar pattern of initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption. In both cases, withdrawal of magma during the eruptions depressurized the shallow storage zone, causing significant volcano-wide subsidence and initiating a new intereruption deformation cycle.

Alaska↗

USGS2010

Ground surface deformation patterns, magma supply, and magma storage at Okmok volcano, Alaska, from InSAR analysis: 2. Coeruptive deflation, July-August 2008

A hydrovolcanic eruption near Cone D on the floor of Okmok caldera, Alaska, began on 12 July 2008 and continued until late August 2008. The eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and ∼3 km below sea level (bsl), which began immediately after Okmok's previous eruption in 1997. In this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar (InSAR) techniques to produce a suite of 2008 coeruption deformation maps. Most of the surface deformation that occurred during the eruption is explained by deflation of a Mogi-type source located beneath the center of the caldera and 2–3 km bsl, i.e., essentially the same source that inflated prior to the eruption. During the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1/ e time constant of ∼13 days. We envision a sponge-like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath Okmok caldera. The rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface. A similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring-fracture system.

Alaska↗

USGS2010

Monitoring and characterizing natural hazards with satellite InSAR imagery

Interferometric synthetic aperture radar (InSAR) provides an all-weather imaging capability for measuring ground-surface deformation and inferring changes in land surface characteristics. InSAR enables scientists to monitor and characterize hazards posed by volcanic, seismic, and hydrogeologic processes, by landslides and wildfires, and by human activities such as mining and fluid extraction or injection. Measuring how a volcano's surface deforms before, during, and after eruptions provides essential information about magma dynamics and a basis for mitigating volcanic hazards. Measuring spatial and temporal patterns of surface deformation in seismically active regions is extraordinarily useful for understanding rupture dynamics and estimating seismic risks. Measuring how landslides develop and activate is a prerequisite to minimizing associated hazards. Mapping surface subsidence or uplift related to extraction or injection of fluids during exploitation of groundwater aquifers or petroleum reservoirs provides fundamental data on aquifer or reservoir properties and improves our ability to mitigate undesired consequences. Monitoring dynamic water-level changes in wetlands improves hydrological modeling predictions and the assessment of future flood impacts. In addition, InSAR imagery can provide near-real-time estimates of fire scar extents and fire severity for wildfire management and control. All-weather satellite radar imagery is critical for studying various natural processes and is playing an increasingly important role in understanding and forecasting natural hazards.

Annals of GIS↗

USGS2010

Radar image and data fusion for natural hazards characterisation

Fusion of synthetic aperture radar (SAR) images through interferometric, polarimetric and tomographic processing provides an all - weather imaging capability to characterise and monitor various natural hazards. This article outlines interferometric synthetic aperture radar (InSAR) processing and products and their utility for natural hazards characterisation, provides an overview of the techniques and applications related to fusion of SAR/InSAR images with optical and other images and highlights the emerging SAR fusion technologies. In addition to providing precise land - surface digital elevation maps, SAR - derived imaging products can map millimetre - scale elevation changes driven by volcanic, seismic and hydrogeologic processes, by landslides and wildfires and other natural hazards. With products derived from the fusion of SAR and other images, scientists can monitor the progress of flooding, estimate water storage changes in wetlands for improved hydrological modelling predictions and assessments of future flood impacts and map vegetation structure on a global scale and monitor its changes due to such processes as fire, volcanic eruption and deforestation. With the availability of SAR images in near real - time from multiple satellites in the near future, the fusion of SAR images with other images and data is playing an increasingly important role in understanding and forecasting natural hazards.

International Journal of Image and Data Fusion↗

USGS2010

Surface deformation of Augustine Volcano, 1992-2005, from multiple-interferogram processing using a refined Small Baseline Subset (SBAS) Interferometric Synthetic Aperture Radar (InSAR) approach: Chapter 18 in The 2006 eruption of Augustine Volcano, Alaska

Augustine Volcano is an active stratovolcano located in southwestern Cook Inlet, about 280 kilometers southwest of Anchorage, Alaska. The volcano produced six significant explosive eruptions between 1812 and 1986. Augustine eruptions typically have an explosive onset followed by dome building. The most recent eruption began on January 11, 2006. We applied the small baseline subset (SBAS) interferometric synthetic aperture radar (InSAR) technique to measure ground surface deformation during 1992-2005 with the use of European Remote Sensing Satellites 1 and 2 (ERS-1 and ERS-2) radar imagery. Through a multiple-interferogram approach, atmospheric delay artifacts, which hinder conventional InSAR measurements, are significantly reduced by spatial and temporal filtering. This allows us to retrieve time-series deformation over coherent points at millimeter-scale accuracy. The deformation results from two independent satellite tracks agree with each other, suggesting 2 to 8 cm wholesale uplift of Augustine Volcano from 1992 to 2005. Global Positioning System (GPS) data acquired in September 2004 and October 2005 confirm the SBAS InSAR results. A preliminary model consisting of a contracting source at 2 to 4 km depth and an inflating source at 7 to 12 km depth fits the observed deformation reasonably well. We interpret the deeper source as a long-term magma storage zone and the shallower source as a subsidiary reservoir that was tapped during the 2006 eruption. The shallow source corresponds approximately to the location of the volcano-tectonic earthquakes that preceded and followed the 1976 and 2006 eruptions, respectively.

Alaska↗

USGS2009

Continuing inflation at Three Sisters volcanic center, central Oregon Cascade Range, USA, from GPS, leveling, and InSAR observations

Uplift of a broad area centered ~6 km west of the summit of South Sister volcano started in September 1997 (onset estimated from model discussed in this paper) and was continuing when surveyed in August 2006. Surface displacements were measured whenever possible since August 1992 with satellite radar interferometry (InSAR), annually since August 2001 with GPS and leveling surveys, and with continuous GPS since May 2001. The average maximum displacement rate from InSAR decreased from 3–5 cm/yr during 1998–2001 to ~1.4 cm/yr during 2004–2006. The other datasets show a similar pattern, i.e., surface uplift and extension rates decreased over time but deformation continued through August 2006. Our best-fit model to the deformation data is a vertical, prolate, spheroidal point-pressure source located 4.9–5.4 km below the surface. The source inflation rate decreased exponentially during 2001–2006 with a 1/ e decay time of 5.3 ± 1.1 years. The net increase in source volume from September 1997 to August 2006 was 36.5–41.9 x 10 6 m 3 . A swarm of ~300 small ( M max = 1.9) earthquakes occurred beneath the deforming area in March 2004; no other unusual seismicity has been noted. Similar deformation episodes in the past probably would have gone unnoticed if, as we suspect, most are small intrusions that do not culminate in eruptions.

Oregon↗

USGS2009

Monitoring lava-dome growth during the 2004–2008 Mount St. Helens, Washington, eruption using oblique terrestrial photography

We present an analysis of lava dome growth during the 2004–2008 eruption of Mount St. Helens using oblique terrestrial images from a network of remotely placed cameras. This underutilized monitoring tool augmented more traditional monitoring techniques, and was used to provide a robust assessment of the nature, pace, and state of the eruption and to quantify the kinematics of dome growth. Eruption monitoring using terrestrial photography began with a single camera deployed at the mouth of the volcano's crater during the first year of activity. Analysis of those images indicates that the average lineal extrusion rate decayed approximately logarithmically from about 8 m/d to about 2 m/d (± 2 m/d) from November 2004 through December 2005, and suggests that the extrusion rate fluctuated on time scales of days to weeks. From May 2006 through September 2007, imagery from multiple cameras deployed around the volcano allowed determination of 3-dimensional motion across the dome complex. Analysis of the multi-camera imagery shows spatially differential, but remarkably steady to gradually slowing, motion, from about 1–2 m/d from May through October 2006, to about 0.2–1.0 m/d from May through September 2007. In contrast to the fluctuations in lineal extrusion rate documented during the first year of eruption, dome motion from May 2006 through September 2007 was monotonic (± 0.10 m/d) to gradually slowing on time scales of weeks to months. The ability to measure spatial and temporal rates of motion of the effusing lava dome from oblique terrestrial photographs provided a significant, and sometimes the sole, means of identifying and quantifying dome growth during the eruption, and it demonstrates the utility of using frequent, long-term terrestrial photography to monitor and study volcanic eruptions.

Washington↗

USGS2008

Remote camera observations of lava dome growth at Mount St. Helens, Washington, October 2004 to February 2006

Images from a Web-based camera (Webcam) located 8 km north of Mount St. Helens and a network of remote, telemetered digital cameras were used to observe eruptive activity at the volcano between October 2004 and February 2006. The cameras offered the advantages of low cost, low power, flexibility in deployment, and high spatial and temporal resolution. Images obtained from the cameras provided important insights into several aspects of dome extrusion, including rockfalls, lava extrusion rates, and explosive activity. Images from the remote, telemetered digital cameras were assembled into time-lapse animations of dome extrusion that supported monitoring, research, and outreach efforts. The wide-ranging utility of remote camera imagery should motivate additional work, especially to develop the three-dimensional quantitative capabilities of terrestrial camera networks.

Washington↗

USGS2008

Constraints and conundrums resulting from ground-deformation measurements made during the 2004-2005 dome-building eruption of Mount St. Helens, Washington

A prolonged period of dome growth at Mount St. Helens starting in September-October 2004 provides an opportunity to study how the volcano deforms before, during, and after an eruption by using modern instruments and techniques, such as global positioning system (GPS) receivers and interferometric synthetic aperture radar (InSAR), together with more traditional ones, including tiltmeters, triangulation, photogrammetry, and time-lapse photography. No precursory ground deformation was detected by campaign GPS measurements made in 2000 and 2003, nor by a continuous GPS station (JRO1) operating ~9 km to the north-northwest of the vent area since May 1997. However, JRO1 abruptly began moving downward and southward, toward a source centered about 8 km beneath the volcano, concurrently with the start of a shallow earthquake swarm on September 23, 2004. The JRO1 velocity slowed from ~0.5 millimeters per day (mm/d) in late September–early October 2004 until spring 2005. Thereafter, it was essentially constant at ~0.04 mm/d through December 2005. In similar fashion, the growth rate of the welt on the south crater floor slowed from 8.9 m 3 /s during October 4–11 to 6.4 m 3 /s during October 11-13, 2004; this trend continued after emergence of the first lava spine on October 11. The volumetric extrusion rate decreased from 5.9 m 3 /s during October 13-November 4, 2004, to 2.5 m 3 /s during December 11, 2004-January 3, 2005, and for the remainder of 2005, it was in the range 2.0-0.7 m 3 /s. Fifteen continuous GPS stations, installed soon after the eruption began, showed radially inward and downward ground motions through December 2005. Likewise, InSAR observations spanning the first year of the eruption indicate broad subsidence centered near the vent. Model-derived estimates of source-volume decrease from September 23, 2004, to October 31, 2006, are 16-24×10 6 m 3 , substantially less than the volume erupted during the same period (87×10 6 m 3 through October 21, 2006). The discrepancy can be explained by a combination of magma expansion and recharge in the source region. Lack of precursory deformation at JRO1 suggests that the conduit is poorly coupled to the rest of the edifice, so the rising magma column was able to push ahead older conduit material rather than intruding it. Constraints on conduit length and radius require that reservoir magma (as opposed to conduit-filling magma) reached the surface early during the eruption, probably soon after CO 2 emission rates peaked in early October 2004. If rapid emergence of spine 3 (the first whaleback-shaped extrusion) in late October 2004 marked the arrival of reservoir magma, then the volume of conduit material flushed from the system was about 20×10 6 m 3 --the volume of surface deformation plus spines on November 4, 2004. The corresponding radius for a cylinder extending from the surface to depth d = 5 km is 35.7 m, or 28.2 m for d = 8 km. The average ascent rate through the conduit, assuming reservoir magma began its rise on September 23, 2004, was 120 m/d for d = 5 km, or 190 m/d for d = 8 km. Observed lineal extrusion rates were 2-10 m/d, so the conduit must widen considerably near the surface. Equating magma flux through the conduit to that at the surface, we obtain a vent radius of 125 m and an extrusion rate of 5.7 m 3 /s--both values representative of the early part of the eruption. Lack of precursory inflation suggests that the volcano was poised to erupt magma already stored in a crustal reservoir when JRO1 was installed in 1997. Trilateration and campaign GPS data indicate surface dilatation, presumably caused by reservoir expansion between 1982 and 1991, but no measurable deformation between 1991 and 2003. We conclude that all three of the traditionally reliable eruption precursors (seismicity, ground deformation, and volcanic gas emission) failed to provide warning that an eruption was imminent until a few days before a visible welt appeared at the surface--a situation reminiscent of the 1980 north-flank bulge at Mount St. Helens.

Washington↗

USGS2008

Analysis of GPS-measured deformation associated with the 2004-2006 dome-building eruption of Mount St. Helens, Washington

Detecting far-field deformation at Mount St. Helens since the crater-forming landslide and blast in 1980 has been difficult despite frequent volcanic activity and improved monitoring techniques. Between 1982 and 1991, the systematic extension of line lengths in a regional GPS trilateration network is consistent with recharge of a deep magma chamber during that interval. The rate of extension, however, averages only 3 mm/yr, and some of this apparent deformation may result from systematic scale error in the electronic distance measurements. Subsequent GPS surveys and data from a continuous GPS station, located 9 km north of Mount St. Helens and operating since 1997, show no significant volcanic deformation until the start of unrest on September 23, 2004. The current eruption has been accompanied by subtle but widespread inward and downward movement of GPS monitoring stations, exponentially decreasing with time and totaling as much as 30 mm. The observed deformation is consistent with the predictions of an elastic half-space model of a vertically elongate magma chamber with its center at a depth of around 7 to 8 km and with a total cavity-volume loss of about 16–24×10 6 m 3 . The discrepancy between the estimated cavity-volume loss and the >83×10 6 -m 3 volume of the erupted dome can be explained, for the most part, by exsolution of gas in the stored magma and by minor input of new magma during the eruption.

Washington↗

USGS2008

Converting NAD83 GPS Heights Into NAVD88 Elevations With LVGEOID, a Hybrid Geoid Height Model for the Long Valley Volcanic Region, California

A GPS survey of leveling benchmarks done in Long Valley Caldera in 1999 showed that the application of the National Geodetic Survey (NGS) geoid model GEOID99 to tie GPS heights to historical leveling measurements would significantly underestimate the caldera ground deformation (known from other geodetic measurements). The NGS geoid model was able to correctly reproduce the shape of the deformation, but required a local adjustment to give a realistic estimate of the magnitude of the uplift. In summer 2006, the U.S. Geological Survey conducted a new leveling survey along two major routes crossing the Long Valley region from north to south (Hwy 395) and from east to west (Hwy 203 - Benton Crossing). At the same time, 25 leveling bench marks were occupied with dual frequency GPS receivers to provide a measurement of the ellipsoid heights. Using the heights from these two surveys, we were able to compute a precise geoid height model (LVGEOID) for the Long Valley volcanic region. Our results show that although the LVGEOID and the latest NGS GEOID03 model practically coincide in areas outside the caldera, there is a difference of up to 0.2 m between the two models within the caldera. Accounting for this difference is critical when using the geoid height model to estimate the ground deformation due to magmatic or tectonic activity in the caldera.

Scientific Investigations Report↗

USGS2007

Volcano deformation--Geodetic monitoring techniques

This book describes the techniques used by volcanologists to successfully predict several recent volcanic eruptions by combining information from various scientific disciplines, including geodetic techniques. Many recent developments in the use of state-of-the-art and emerging techniques, including Global Positioning System and Synthetic Aperture Radar Interferometry, mean that most books on volcanology are out of date, and this book includes chapters devoted entirely to these two techniques.

Book↗