Geology topics

Jacqueline Caplan-Auerbach

Publications and source records attributed to Jacqueline Caplan-Auerbach.

7 recordsLinked to original sources

USGS2026

A 481 m-high landslide-tsunami in a cruise ship-frequented Alaska fjord

Early in the morning of 10 August 2025, a >64 × 10 6 –cubic meter landslide struck Tracy Arm fjord in Alaska. The landslide was preconditioned by glacial retreat caused by climate change. The resulting 481-meter runup megatsunami followed an initial 100-meter-high breaking wave traveling at >70 meters per second. The landslide was preceded by several days of microseismicity, which increased in rate and magnitude until ~1 hour before failure. The landslide produced globally observed long-period seismic waves equivalent in size to a moment magnitude 5.4 earthquake. A long-period (~66 second) global seismic signal, produced by a landslide-induced seiche trapped within the fjord, persisted for up to 36 hours, the second time a days-long seiche had thus been observed. With fjord regions increasingly visited by cruise ships, and climate change making similar events more likely, this unanticipated, near-miss event highlights the growing risk from landslides and tsunamis in coastal environments.

Alaska↗

USGS2019

Seismic and acoustic signatures of surficial mass movements at volcanoes

Surficial mass movements, such as debris avalanches, rock falls, lahars, pyroclastic flows, and outburst floods, are a dominant hazard at many volcanoes worldwide. Understanding these processes, cataloging their spatio-temporal occurrence, and detecting, tracking, and characterizing these events would advance the science of volcano monitoring and help mitigate hazards. Seismic and acoustic methods show promise for achieving these objectives: many surficial mass movements generate observable seismic and acoustic signals, and many volcanoes are already monitored. Significant progress has been made toward understanding, modeling, and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements. However, much work remains. In this paper, we review the state of the art of the topic, covering a range of scales and event types from individual rock falls to sector collapses. We consider a full variety of volcanic settings, from submarine to subaerial, shield volcano to stratovolcano. Finally, we discuss future directions toward operational seismo-acoustic monitoring of surficial mass movements at volcanoes.

Journal of Volcanology and Geothermal Research↗

USGS2017

Precursory seismicity associated with frequent, large ice avalanches on Iliamna Volcano, Alaska, USA

Since 1994, at least six major (volume>106 m 3 ) ice and rock avalanches have occurred on Iliamna volcano, Alaska, USA. Each of the avalanches was preceded by up to 2 hours of seismicity believed to represent the initial stages of failure. Each seismic sequence begins with a series of repeating earthquakes thought to represent slip on an ice-rock interface, or between layers of ice. This stage is followed by a prolonged period of continuous ground-shaking that reflects constant slip accommodated by deformation at the glacier base. Finally the glacier fails in a large avalanche. Some of the events appear to have entrained large amounts of rock, while others comprise mostly snow and ice. Several avalanches initiated from the same source region, suggesting that this part of the volcano is particularly susceptible to failure, possibly due to the presence of nearby fumaroles. Although thermal conditions at the time of failure are not well constrained, it is likely that geothermal energy causes melting at the glacier base, promoting slip and culminating in failure. The frequent nature and predictable failure sequence of Iliamna avalanches makes the volcano an excellent laboratory for the study of ice avalanches. The prolonged nature of the seismic signal suggests that warning may one day be given for similar events occurring in populated regions.

Alaska↗

USGS2011

Magma at depth: A retrospective analysis of the 1975 unrest at Mount Baker, Washington, USA

Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements suggest slight deflation of the edifice between 1981-83 and 2006-07. The volcano remains seismically quiet with regard to impulsive volcano-tectonic events, but experiences shallow (<3 km) low-frequency events likely related to glacier activity, as well as deep (>10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential to this assessment of magmatic activity.

Mount Baker Volcano↗

USGS2008

Seismicity associated with renewed dome building at Mount St. Helens, 2004-2005

The reawakening of Mount St. Helens after 17 years and 11 months of slumber was heralded by a swarm of shallow (depth <2 km) volcano-tectonic earthquakes on September 23, 2004. After an initial decline on September 25, seismicity rapidly intensified; by September 29, M d >2 earthquakes were occurring at a rate of ~1 per minute. A gradual transition from volcano-tectonic to hybrid and low-frequency events occurred along with this intensification, a characteristic of many precursory swarms at Mount St. Helens before dome-building eruptions in the 1980s. The first explosion occurred October 1, 2004, 8.5 days after the first earthquakes, and was followed by three other explosions over the next four days. Seismicity declined after each explosion and after two energetic noneruptive tremor episodes on October 2 and 3. Following the last explosion of this series, on October 5, seismicity declined significantly. Over the next ten days seismicity was dominated by several event families; by October 16, spacing between events had become so regular that we dubbed the earthquakes “drumbeats.” Through the end of 2005 seismicity was dominated by these drumbeats, although occasional larger earthquakes ( M d 2.0-3.4) dominated seismic energy release. Over time there were significant variations in drumbeat size, spacing, and spectra that correlated with changes in the style of extrusion at the surface. Changes in drumbeat character did not correspond to variations in magma flux at the conduit, indicating that drumbeat size and spacing may be more a function of the mechanics of extrusion than of the extrusion rate.

Washington↗

USGS2006

Basaltic thermals and Subplinian plumes: Constraints from acoustic measurements at Shishaldin volcano, Alaska

The 1999 basaltic eruption of Shishaldin volcano (Alaska, USA) included both Strombolian and Subplinian activity, as well as a “pre-Subplinian” phase interpreted as the local coalescence within a long foam in the conduit. Although few visual observations were made of the eruption, a great deal of information regarding gas velocity, gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption. By relating acoustic power to gas velocity, a time series of gas velocity is calculated for the Subplinian and pre-Subplinian phases. These time series show trends in gas velocity that are interpreted as plumes or, for those signals lasting only a short time, thermals. The Subplinian phase is shown to be composed of a thermal followed by five plumes with a total expelled gas volume of ≈ 1.5 × 10 7 m 3 "> ≈ 1.5 × 10 7 m 3 . The initiation of the Subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column. A gradual increase in low-frequency (0.01–0.5 Hz) signal prior to this “trigger bubble” may be due to the rise of the bubble in the conduit. This delay corresponds to a reservoir located at ≈3.9 km below the surface, in good agreement with studies on other volcanoes. The presence of two thermal phases is also identified in the middle of the pre-Subplinian phase with a total gas release of ≈ 4.3 × 10 6 m 3 "> ≈ 4.3 × 10 6 m 3 and ≈ 3.6 × 10 6 m 3 "> ≈ 3.6 × 10 6 m 3 . Gas velocity at the vent is found to be ≈ 82 m . s − 1 "> ≈ 82 m . s − 1 and ≈ 90 m . s − 1 "> ≈ 90 m . s − 1 for the Subplinian plumes and the pre-Subplinian thermals respectively. The agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements, leading to a new method by which eruption physical parameters may be quantified. Furthermore, direct measurements of gas velocity can be used for better estimates of the S O 2 "> S O 2 flux released during the eruption.

Alaska↗

USGS2006

Sustained long-period seismicity at Shishaldin Volcano, Alaska

From September 1999 through April 2004, Shishaldin Volcano, Aleutian Islands, Alaska, exhibited a continuous and extremely high level of background seismicity. This activity consisted of many hundreds to thousands of long-period (LP; 1–2 Hz) earthquakes per day, recorded by a 6-station monitoring network around Shishaldin. The LP events originate beneath the summit at shallow depths (0–3 km). Volcano tectonic events and tremor have rarely been observed in the summit region. Such a high rate of LP events with no eruption suggests that a steady state process has been occurring ever since Shishaldin last erupted in April–May 1999. Following the eruption, the only other signs of volcanic unrest have been occasional weak thermal anomalies and an omnipresent puffing volcanic plume. The LP waveforms are nearly identical for time spans of days to months, but vary over longer time scales. The observations imply that the spatially close source processes are repeating, stable and non-destructive. Event sizes vary, but the rate of occurrence remains roughly constant. The events range from magnitude ∼0.1 to 1.8, with most events having magnitudes <1.0. The observations suggest that the conduit system is open and capable of releasing a large amount of energy, approximately equivalent to at least one magnitude 1.8–2.6 earthquake per day. The rate of observed puffs (1 per minute) in the steam plume is similar to the typical seismic rates, suggesting that the LP events are directly related to degassing processes. However, the source mechanism, capable of producing one LP event about every 0.5–5 min, is still poorly understood. Shishaldin's seismicity is unusual in its sustained high rate of LP events without accompanying eruptive activity. Every indication is that the high rate of seismicity will continue without reflecting a hazardous state. Sealing of the conduit and/or change in gas flux, however, would be expected to change Shishaldin's behavior.

Alaska↗