02129nas a2200253   4500008004100000020001400041022001300055245010000068210006900168260000800237300001100245490000800256520137600264100001701640700001501657700002301672700001901695700002101714700001601735700002201751700002001773700002101793856006101814       2008                        eng d  a0148-0227  a2169901100a{Ice-front variation and tidewater behavior on Helheim and Kangerdlugssuaq Glaciers, Greenland}0 aIcefront variation and tidewater behavior on Helheim and Kangerd  cjan  a1–110 v1133 aWe used satellite images to examine the calving behavior ofHelheim and Kangerdlugssuaq Glaciers, Greenland, from 2001 to 2006, a period in which they retreated and speed up. These data show that many large iceberge-calving episodes coincided with teleseismically detected glacial erthquakes, suggesting that calving-related processes are the source of seismicity. For each of several events for which we hace observations, the ice front calved back to a large, pre-existing rift. These refits form where the ice has thinned to near flotation as the ice front retreats down back side of a bathymetric high, which agrees well with earlier theoretical predictions. In adition to recent retreat in a period of high temperature, analysis of several images shows that Helhaim retreated in the 20th Century during a warmer period and then re-adcanced during a subsequent cooler period. This apparent sensitivity to waming suggests that higher temperatures may promote an initial retread off a bathymetric high that is then sustained by tidewater dynamics as the ice front retreats into depper water. The cycle of frontal advance and retreat in less than a century indicates that tidewater glaciers in Greenland can advance rapidly. Greenland's larger resorvoir of inland ice and conditions that favor the formation of ice shelves likely contribute to the rapid rates of advance.1 aJoughin, Ian1 aHowat, Ian1 aAlley, Richard, B.1 aEkstrom, Goran1 aFahnestock, Mark1 aMoon, Twila1 aNettles, Meredith1 aTruffer, Martin1 aTsai, Victor, C.  uhttp://www.agu.org/pubs/crossref/2008/2007JF000837.shtml