Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland

Clarke, T. S.; Echelmeyer, Κ. A.

doi:10.1017/s0022143000004081

Cited by 89 publications

(74 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…5) and, since 1993, over the main, southern trunk. Thickness measurements along the northern survey line show the bed to be close to sea level, but seismic measurements made in the 1980s (Clarke and Echelmeyer, 1996) show that the fastest part of the glacier covered by our southern survey line flows in a deep trough, more than 1000 m below sea level (Fig. 5c).…”

Section: Jakobshavn Isbraementioning

confidence: 80%

See 1 more Smart Citation

Recent changes on Greenland outlet glaciers

Thomas¹,

Frederick²,

Krabill

et al. 2009

J. Glaciol.

View full text Add to dashboard Cite

Aircraft laser-altimeter surveys during the 1990s showed near-coastal parts of the Greenland ice sheet to be thinning; despite slow thickening at higher elevations, the ice sheet lost mass to the ocean. Many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers, indicating dynamic imbalance between glacier velocity and upstream snow accumulation. Results from more recent surveys, presented here, show that thinning rates have increased in most coastal regions. For almost half of the surveys, these increases might have resulted from increases in summer melting, but rapid thinning on others is indicative of dynamic changes that increased with time. In particular, thinning rates on the three fastest glaciers increased to tens of m a -1 after 2000, and other observations show an approximate doubling in their velocities. The deep beds of these glaciers appear to have a strong influence on rates of grounding-line retreat and thickness change, with periods of glacier acceleration and rapid thinning initiated by flotation and break-up of lightly grounded glacier snouts or break-up of floating ice tongues. Near-simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause. Nearby glaciers without deep beds are thinning far more slowly, suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on Greenland outlet-glacier acceleration

show abstract

Section: Jakobshavn Isbraementioning

confidence: 80%

“…Seismic data from Jakobshavn Isbrae (Clarke and Echelmeyer, 1996) and results from radar depth sounding (Plummer and others, 2008) also show a very deep bed. Here, creep thinning of the glacier might have increased following a reduction in the buttressing effects of a downstream floating tongue .…”

mentioning

confidence: 85%

Recent changes on Greenland outlet glaciers

Thomas¹,

Frederick²,

Krabill

et al. 2009

J. Glaciol.

View full text Add to dashboard Cite

show abstract

“…Accelerated by the force differential created by the disappearing support, the dislodged ice slips seismically along the contact between the ice and the wall rock of the U-shaped deep glacial trough (Clarke and Echelmeyer, 1996) that underlies the ice stream. Synthetic seismograms and the radiation pattern from the events studied suggest that the seismogenic slippage that produces the culminating events occurs along the margin of the ice stream, and could be produced by a large mass-wasting event.…”

Section: Rumbling Characteristics and Dynamic Interpretationmentioning

confidence: 99%

“…1a). At its epicenter, the ice-stream margin is oriented 708 from north, and the slope of the trough wall in this locality is 60-708 (Clarke and Echelmeyer, 1996). These facts were used to approximate the geometry of the rupture surface and construct synthetic seismograms for the event.…”

Section: Rumbling Characteristics and Dynamic Interpretationmentioning

confidence: 99%

Glacial rumblings from Jakobshavn ice stream, Greenland

Rial¹,

Tang²,

Steffen

2009

J. Glaciol.

View full text Add to dashboard Cite

The steep increase in Greenland's glacial earthquake activity detected by the Global Seismographic Network since the late 1990s suggests that a close inspection of these events might provide clues to the nature and origin of such seismic activity. Here we discuss the detection of large, unexpected seismic events of extraordinarily long duration (10-40 min) occurring about once every 2 days, and localized in the ice stream that feeds the Earth's fastest-moving glacier (Jakobshavn Isbrae) from the east. These 'glacial rumblings' represent an ice-mass wasting process that is greater and more frequent than glacial earthquakes have suggested. Probably triggered by calving, the rumblings are all very similar regardless of duration, and all end with a sharp, earthquake-like event in which the largest seismic amplitude is in the rumbling and that might signal the collapse of large ice masses upstream. By calculating the total amount of seismic energy released as rumblings, we estimate that the maximum seasonal amount of ice moved seismogenically down the ice stream is up to 12 km 3 , or $30% of the average annual iceberg discharge in Jakobshavn.

show abstract

“…Furthermore, whereas the observational record has focused almost exclusively on the calving terminus of the glacier, geological studies can also address changes in the land-terminating ice margin near Jakobshavn Isbrae, thus elucidating broader ice-margin responsiveness to climate change. on June 3, 2015 geology.gsapubs.org Downloaded from addition, the Jakobshavn Isbrae bed is more than 1 km below sea level for at least 70 km inland (Clarke and Echelmeyer, 1996). The ice-free landscape between Disko Bugt and the present ice margin consists of glacially scoured bedrock, erratic boulders, and the prominent Fjord Stade moraine complex (Fig.…”

Section: Introductionmentioning

confidence: 98%