Glacial Ice Streams Move with Earthquake Impact

It has been the scientific belief and model that ice streams flowing from the interior of seasonally melting ice sheets moved in a steady creeping motion; picture an ice cube sliding across a table. Seismic recording research shows that that model is a guess that wasn't good enough.

Research that was done in West Antarctica recorded seismic waves at Magnitude 7 that were felt as far away as Australia, which is 4,000 miles (6,400 kilometers) away from the Whillians Ice Stream in West Antarctica. Magnitudes 7.0 to 7.9 are classed as major seismic events.

It is hoped that studies of the Whillians Ice Stream will carry over to the movements of other ice streams, in which case, it will radically change ice stream movement models. The significance of this is that present ice movement models very poorly predict sea level reaction to increased ice sheet melting, which has been steadily raising sea levels. When sea levels rise, land is lost: it is either overwhelmed by ocean waters as in Fiji, or its stability is compromised and it collapses as in Alaska.

Ice streams are the gigantic flows of melting ice that originate in the interior of an ice sheet during warm seasons and flow down the ice sheet to the ocean. These flows don't melt enough to produce streams of water, just moving streams of melting ice.

The new findings indicate that ice streams move in sudden and dramatic events at least twice a day in which the streaming ice lurches ahead by means of earthquake-like patterns of shifts, or "stick-slips," that produce far-reaching Magnitude 7 tremblors. The process seems to be one whereby the ice shifts to a new spot, sticks, accumulates a melt-pool, then slips ahead again.

When stick-slips occur, seemingly in response to tidal variations, people standing on the surface can't feel the quake as they would do if the quake were occurring on land. The reason for the difference between these icequakes and earthquakes is primarily one of duration: earthquakes occur intensely in a mater of seconds but icequakes are prolonged and span about 25 minutes, during which time the ice stream moves about 2.2 feet, or .67 meters.

This study has no direct bearing on understanding global warming but it has significant importance to model generated calculations of just what we are in for as ice sheet melting continues to accelerate due to man-made global escalation of previously natural planetary variations. We need reliable models predicting how fast ocean waters will rise so endangered islands can be successfully evacuated, which requires governments like New Zealand and Australia developing government policy pertaining to evacuees and evacuation assistance.

Resource: http://www.nsf.gov/news/news_summ.jsp?cntn_id=111647&govDel=USNSF_51