Geology topics

Martin Truffer

Publications and source records attributed to Martin Truffer.

5 recordsLinked to original sources

USGS2021

The imminent calving retreat of Taku Glacier

Along the rugged Southeast Alaska coast, 30 kilometers northeast of the state capital Juneau, a tidewater glacier has largely defied global trends by steadily advancing for most of the past century while most glaciers on Earth retreated. This 55-kilometer-long and nearly 1,500-meter-thick tidewater glacier, named Taku Glacier, or T'aaḵú Ḵwáan Sít'i in the language of the Indigenous Tlingit people, has been the focus of continuous scientific study for more than 70 years. Some records even extend back to the mid-18th century. With this long observation record and the glacier’s year-round accessibility and proximity to Juneau and adjacent research facilities, Taku provides an unparalleled locale to study tidewater glaciers and their response to Earth’s rapidly changing climate.

Eos, American Geophysical Union↗

USGS2017

Glacier-volcano interactions in the north crater of Mt. Wrangell, Alaska

Glaciological and related observations from 1961 to 2005 at the summit of Mt Wrangell (62.008 N, 144.028W; 4317 m a.s.l.), a massive glacier-covered shield volcano in south-central Alaska, show marked changes that appear to have been initiated by the Great Alaska Earthquake (MW = 9.2) of 27 March 1964. The 4 x 6 km diameter, ice-filled Summit Caldera with several post-caldera craters on its rim, comprises the summit region where annual snow accumulation is 1–2 m of water equivalent and the mean annual temperature, measured 10 m below the snow surface, is –20°C. Precision surveying, aerial photogrammetry and measurements of temperature and snow accumulation were used to measure the loss of glacier ice equivalent to about 0.03 km 3 of water from the North Crater in a decade. Glacier calorimetry was used to calculate the associated heat flux, which varied within the range 20–140W m –2 ; total heat flow was in the range 20–100 MW. Seismicity data from the crater’s rim show two distinct responses to large earthquakes at time scales from minutes to months. Chemistry of water and gas from fumaroles indicates a shallow magma heat source and seismicity data are consistent with this interpretation.

Alaska↗

USGS2015

Tidal and seasonal variations in calving flux observed with passive seismology

The seismic signatures of calving events, i.e., calving icequakes, offer an opportunity to examine calving variability with greater precision than is available with other methods. Here using observations from Yahtse Glacier, Alaska, we describe methods to detect, locate, and characterize calving icequakes. We combine these icequake records with a coincident, manually generated record of observed calving events to develop and validate a statistical model through which we can infer iceberg sizes from the properties of calving icequakes. We find that the icequake duration is the single most significant predictor of an iceberg's size. We then apply this model to 18 months of seismic recordings and find elevated iceberg calving flux during the summer and fall and a pronounced lull in calving during midwinter. Calving flux is sensitive to semidiurnal tidal stage. Large calving events are tens of percent more likely during falling and low tides than during rising and high tides, consistent with a view that deeper water has a stabilizing influence on glacier termini. Multiple factors affect the occurrence of mechanical fractures that ultimately lead to iceberg calving. At Yahtse Glacier, seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on iceberg calving rates at seasonal timescales. On hourly to daily timescales, tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near-terminus stress field.

Alaska↗

USGS2012

Analysis of low-frequency seismic signals generated during a multiple-iceberg calving event at Jakobshavn Isbræ, Greenland

We investigated seismic signals generated during a large-scale, multiple iceberg calving event that occurred at Jakobshavn Isbræ, Greenland, on 21 August 2009. The event was recorded by a high-rate time-lapse camera and five broadband seismic stations located within a few hundred kilometers of the terminus. During the event two full-glacier-thickness icebergs calved from the grounded (or nearly grounded) terminus and immediately capsized; the second iceberg to calve was two to three times smaller than the first. The individual calving and capsize events were well-correlated with the radiation of low-frequency seismic signals (<0.1 Hz) dominated by Love and Rayleigh waves. In agreement with regional records from previously published ‘glacial earthquakes’, these low-frequency seismic signals had maximum power and/or signal-to-noise ratios in the 0.05–0.1 Hz band. Similarly, full waveform inversions indicate that these signals were also generated by horizontal single forces acting at the glacier terminus. The signals therefore appear to be local manifestations of glacial earthquakes, although the magnitudes of the signals (twice-time integrated force histories) were considerably smaller than previously reported glacial earthquakes. We thus speculate that such earthquakes may be a common, if not pervasive, feature of all full-glacier-thickness calving events from grounded termini. Finally, a key result from our study is that waveform inversions performed on low-frequency, calving-generated seismic signals may have only limited ability to quantitatively estimate mass losses from calving. In particular, the choice of source time function has little impact on the inversion but dramatically changes the earthquake magnitude. Accordingly, in our analysis, it is unclear whether the smaller or larger of the two calving icebergs generated a larger seismic signal.

Journal of Geophysical Research↗

USGS2010

Glacier microseismicity

We present a framework for interpreting small glacier seismic events based on data collected near the center of Bering Glacier, Alaska, in spring 2007. We find extremely high microseismicity rates (as many as tens of events per minute) occurring largely within a few kilometers of the receivers. A high-frequency class of seismicity is distinguished by dominant frequencies of 20–35 Hz and impulsive arrivals. A low-frequency class has dominant frequencies of 6–15 Hz, emergent onsets, and longer, more monotonic codas. A bimodal distribution of 160,000 seismic events over two months demonstrates that the classes represent two distinct populations. This is further supported by the presence of hybrid waveforms that contain elements of both event types. The high-low-hybrid paradigm is well established in volcano seismology and is demonstrated by a comparison to earthquakes from Augustine Volcano. We build on these parallels to suggest that fluid-induced resonance is likely responsible for the low-frequency glacier events and that the hybrid glacier events may be caused by the rush of water into newly opening pathways.

Alaska↗