Calving icebergs: A source of low‐frequency seismic signals from Columbia Glacier, Alaska

Qamar, Anthony

doi:10.1029/jb093ib06p06615

Cited by 68 publications

(95 citation statements)

References 16 publications

(4 reference statements)

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“…It is also possible that we observe parts of the acoustic signal of an event coupled with the ice surface in addition to direct seismic waves (Richardson et al, 2010 Two different general types of glacier-related seismic events close to the terminus, measured at local distances as in our study (i.e. several kilometers from terminus), have been consistently observed by several studies at the Columbia glacier, Alaska (Qamar, 1988;Walter et al, 2010) and on Greenland . Emergent, 2 s to several minutes long signals have been related to directly observed iceberg calving.…”

Section: Seismic Signal Characteristicsmentioning

confidence: 58%

“…Calving events are often described as emergent low-frequency narrow-band (1-3 Hz) seismic signals (Qamar, 1988;, and impulsive, high-frequency acoustic arrivals when measured close to the glacier front (Richardson et al, 2010). As sources, fluid-filled cracks and fracture processes before the calving or the detachment itself, followed by overturning and scraping of icebergs on the ocean seafloor (Amundson et al, 2008) have been suggested.…”

Section: Introductionmentioning

confidence: 99%

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Autonomous detection of calving-related seismicity at Kronebreen, Svalbard

et al. 2012

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Abstract. We detect and cluster waveforms of seismic signals recorded close to the calving front of Kronebreen, Svalbard, to identify glacier-related seismic events and to investigate their relation to calving processes. Single-channel geophone data recorded over several months in 2009 and 2010 are combined with eleven days of direct visual observations of the glacier front. We apply a processing scheme which combines conventional seismic event detection using a sensitive trigger algorithm and unsupervised clustering of all detected signals based on their waveform characteristics by means of Self-Organizing Maps (SOMs). About 10 % of the directly observed calving events close to the geophone (<1 km) can be correlated with seismic detections. We are able to distinguish between false detections, instrumental artifacts, and three classes of signals which are, with different degrees of uncertainty, emitted by calving or glacier activity in general. By extrapolating the interpretation of seismic event classes beyond the time period of visual observations, the temporal distribution of glacier-related events shows an increase in event rate in autumn, particularly for the class which is related to iceberg calving. Using the seismic event distribution in this class as a proxy for the calving rate and measurements of glacier velocity and glacier front position, we discuss the possible relationship between glacier dynamics and calving processes at Kronebreen.

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Section: Seismic Signal Characteristicsmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Autonomous detection of calving-related seismicity at Kronebreen, Svalbard

et al. 2012

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“…Our limited dataset, along with the data of Qamar (1988) and Warren and others (1995), indicates that there is little or no correlation between semi-diurnal tidal fluctuations and calving. This seems surprising in view of the fact that semi-diurnal tidal variations are about 5 m, about one-fifth of the average height above buoyancy.…”

Section: 33tidal Forcingmentioning

confidence: 99%

“…Brown and others, 1982;Meier and Post, 1987;Van der Veen, 1996), with less attention given to seasonal changes (Sikonia, 1982;Vieli and others, 2002) and even less to individual calving events (e.g. Qamar, 1988;Warren and others,1995;Motyka,1997).…”

Section: Introductionmentioning

confidence: 99%

Short-term variations in calving of a tidewater glacier: LeConte Glacier, Alaska, U.S.A.

2003

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ABSTRACT. Knowledge of iceberg calving is important for understanding instabilities of tidewater glaciers and ice sheets. Since 1995 the terminus of LeConte Glacier, Alaska, U.S.A., has retreated about 2 km and the glacier has thinned approximately 120 m at its 1999 terminus position. Our focus is short-term (hours to weeks) variability of the frequency and magnitude of calving events and calving flux. Both photogrammetric and visual observations are employed in a temporal analysis over a several-week period. We combined these data with measurements of ice speed, tide level, surface water input and water-storage estimates in an attempt to better understand the calving process. Contrary to results obtained over longer time-scales on other glaciers, our results show no correlation between ice speed and the frequency of calving. However, calving events do not appear to occur randomly; often they are a response to measurable changes in other parameters within the terminus region. Caclving can often be attributed to buoyancy perturbations and possibly flexure of the nearly floating terminus. Given the multiple possibilities for buoyancy perturbations, we have found no simple relationship between any specific forcing parameter and calving at short time-scales.

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“…Initial studies using sensors with limited frequency bands focused on high-frequency components (>1 Hz) of regional calving seismograms (e.g. Qamar, 1988). More recently, such high-frequency signals with narrowband character (1-5 Hz) have been associated with interactions between detaching icebergs and the sea surface ( Bartholomaus and others, 2012) as well as various englacial fracture mechanisms that are active during calving events (e.g.…”

Section: Introductionmentioning

confidence: 99%

Calving event detection by observation of seiche effects on the Greenland fjords

2013

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ABSTRACT. With mass loss from the Greenland ice sheet accelerating and spreading to higher latitudes, the quantification of mass discharge in the form of icebergs has recently received much scientific attention. Here we make use of very low-frequency (0.001-0.01 Hz) seismic data from three permanent broadband stations installed in the summers of 2009-10 in northwest Greenland in order to monitor local calving activity. At these frequencies, calving seismograms are dominated by a tilt signal produced by local ground flexure in response to fjord seiching generated by major iceberg calving events. A simple triggering algorithm is proposed to detect calving events from large calving fronts with potentially no user interaction. Our calving catalogue identifies spatial and temporal differences in calving activity between Jakobshavn Isbrae and glaciers in the Uummannaq district 200 km to the north. The Uummannaq glaciers show clear seasonal fluctuations in seiche-based calving detections as well as seiche amplitudes. In contrast, the detections at Jakobshavn Isbrae show little seasonal variation, which may be evidence for an ongoing transition to winter calving activity. The results offer further evidence that seismometers can provide efficient and inexpensive monitoring of calving fronts.

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Calving icebergs: A source of low‐frequency seismic signals from Columbia Glacier, Alaska

Cited by 68 publications

References 16 publications

Autonomous detection of calving-related seismicity at Kronebreen, Svalbard

Autonomous detection of calving-related seismicity at Kronebreen, Svalbard

Short-term variations in calving of a tidewater glacier: LeConte Glacier, Alaska, U.S.A.

Calving event detection by observation of seiche effects on the Greenland fjords

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