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Elliot T. Endo

Publications and source records attributed to Elliot T. Endo.

6 recordsLinked to original sources
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↗
USGS2006

Geodetic observations and modeling of magmatic inflation at the Three Sisters volcanic center, central Oregon Cascade Range, USA

Tumescence at the Three Sisters volcanic center began sometime between summer 1996 and summer 1998 and was discovered in April 2001 using interferometric synthetic aperture radar (InSAR). Swelling is centered about 5 km west of the summit of South Sister, a composite basaltic-andesite to rhyolite volcano that last erupted between 2200 and 2000 yr ago, and it affects an area ∼20 km in diameter within the Three Sisters Wilderness. Yearly InSAR observations show that the average maximum displacement rate was 3–5 cm/yr through summer 2001, and the velocity of a continuous GPS station within the deforming area was essentially constant from June 2001 to June 2004. The background level of seismic activity has been low, suggesting that temperatures in the source region are high enough or the strain rate has been low enough to favor plastic deformation over brittle failure. A swarm of about 300 small earthquakes ( M max = 1.9) in the northeast quadrant of the deforming area on March 23–26, 2004, was the first notable seismicity in the area for at least two decades. The U.S. Geological Survey (USGS) established tilt-leveling and EDM networks at South Sister in 1985–1986, resurveyed them in 2001, the latter with GPS, and extended them to cover more of the deforming area. The 2001 tilt-leveling results are consistent with the inference drawn from InSAR that the current deformation episode did not start before 1996, i.e., the amount of deformation during 1995–2001 from InSAR fully accounts for the net tilt at South Sister during 1985–2001 from tilt-leveling. Subsequent InSAR, GPS, and leveling observations constrain the source location, geometry, and inflation rate as a function of time. A best-fit source model derived from simultaneous inversion of all three datasets is a dipping sill located 6.5 ± 2.5 km below the surface with a volume increase of 5.0 × 10 6 ± 1.5 × 10 6 m 3 /yr (95% confidence limits). The most likely cause of tumescence is a pulse of basaltic magma intruding the upper crust along the brittle–ductile interface — a process that must occur episodically beneath the Cascade Range but in the past would have escaped detection in the absence of unusual seismicity. We speculate that such intrusive episodes last from days to years and are separated by quiescent periods of decades to centuries. The likelihood that the current episode at Three Sisters will culminate in an eruption is judged to be low, but the impact of an eruption could be great. The USGS has updated its volcano hazards assessment for the Three Sisters region, notified appropriate agencies and the public, and is helping to prepare an emergency coordination and communication plan.

Central Oregon Cascade Range, Three Sisters volcan↗
USGS1983

Surface deformation in volcanic rift zones

The principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes, some of which feed fissure eruptions. Elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression. Concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift. If eruption occurs the characteristic ridge-trough-ridge displacement profile changes to a single ridge, centered at the fissure, and the erupted lava alters the local topography. A well-developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events. To investigate this process we compute the elastic displacements and stresses in a homogeneous, two-dimensional half-space driven by a pressurized crack that may breach the surface. A derivative graphical method permits one to estimate the three geometric parameters of the dike (height, inclination, and depth-to-center) and the mechanical parameter (driving pressure/rock stiffness) from a smoothly varying displacement profile. Direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation, notably normal faulting, creates discontinuities in the profile. Geological structures (open cracks, normal faults, buckles, and thrust faults) form because of stresses induced by dike emplacement and fissure eruption. Theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation.

Tectonophysics↗
USGS1974

Development and evaluation of a prototype global volcanic surveillance system utilizing the ERTS-1 satellite data collection system

The ERTS Data Collection System makes it feasible for the first time to monitor the level of activity at widely separated volcanoes and to relay these data rapidly to one central office for analysis. This capability opens a new era in volcanology where the hundreds of normally quiescent but potentially dangerous volcanoes near populated regions around the world can be economically and reliably monitored daily to warn when any one volcano is becoming active again. Before ERTS was launched only a few volcanoes in the world were monitored continuously because of the high cost of building and staffing volcano observatories. Yet it is known from data collected in this century, that while visible signs of pending eruptions may occur only minutes to days in advance, invisible but measurable signs may be detected days, weeks, months and even years before a major eruption. While prediction of specific eruptions is still an elusive goal, early warning of a reawakening of activity at quiescent volcanoes is now a distinct possibility. A prototype volcano surveillance system was established during the latter part of 1972 and early 1973 on 15 volcanoes in Alaska, Hawaii, Washington, California, Iceland, Guatemala, El Salvador, and Nicaragua. Nineteen seismic detectors that count four different sizes of earthquakes and six biaxial borehole tiltmeters that measure ground tilt with a resolution of 1 microradian have been installed. Data from these instruments are relayed through the ERTS satellite and through a teletype link to the U.S. Geological Survey Office in Menlo Park for rapid analysis. Only seismic and tilt data are collected because these have been shown in the past to indicate most reliably the level of volcanic activity and also because they can be measured relatively easily with available instrumentation. Experience during this project demonstrates the feasibility of building inexpensive, low power, reliable instruments that can be installed in remote locations and can be expected to run unattended for a few years. Comparison of the data from these new earthquake counters with data from nearby standard seismometers shows that the counters do normally indicate the level of seismic activity. During periods of high seismic background noise there may be a significant number of spurious counts but the existence and duration of such noisy periods are reliably indicated by other data collected by the earthquake counters. An eruption of Volcan Fuego in Guatemala was preceded by an order of magnitude increase in the number of seismic-event counts several days before. The tiltmeters operated stably in several different environments. A twenty-microradian collapse of the summit of Kilauea Volcano in Hawaii was observed on three tiltmeters. This initial experiment shows that now with the advent of inexpensive satellite telemetry it is both technologically and economically feasible to build a global volcano surveillance system. Several details in the design and deployment of appropriate low-power, inexpensive, and reliable instruments still need to be worked out. Work continues to evaluate the scientific feasibility of this system by collecting and analyzing data that clearly demonstrate the ability of this system to detect changes in volcanic activity.

Open-File Report↗