Tiningnilik Glacier Lake, Greenland

Tininglilik ( also-Tininnilik) is a glacier dammed lake onn the southern margin of the Sarqardliup Sermia 30 km south of Jakobshavn Glacier. I first examined this lake during the UMaine research program on Jakobshavn in 1985. The lake periodically drains and refills over an approximate 10 year period. The lake has an area of 43 square kilometers when full and 20 km2 when empty, each emptying phase releases 2-3 cubic kilometers of water. The lake is filled mostly by subglacial input derived from surface melt, much from supraglacial lake drainage, which makes June and July the main months for refilling. The lake drainage and refilling in 1993 and 2003 was examined by Furuya and Wahr (2005). They expanded on the work of Roger Braithwaite and Henrik Thomsen who had identified five lake drain-fill cycles from 1945-1983. In discussing this with them in Norway in 1986 I noted that the lake was not yet refilled, three years after the last drainage. They suggested that the lake had always filled relatively slowly and drained quickly. After the 1993 discharge 1997 fieldwork noted the lake was still not close to full. A 2000 Landsat image (first image) indicates the lake full, with the yellow and red arrows indicating key locations for differentiation when the lake is drained and filling. After the 2003 drainage, by 2005 the lake had filled somewhat (second image), in 2007 (third image) the lake is 70% full in terms of area and by 2009 the lake was full (fourth image). In the 2005 image the former lake elevation is seen as a sharp transition from pink to green, this is the lake trimline. The lake drained between the June 14 (top) and August 19th (middle) Landsat images from 2010, so lake drainage occurs in a matter of weeks. A further image from July 2011 indicates the slow rate of refilling of the lake. By June 12 2012 the lake is still not occupying the north trending arm at the red arrow (last image), this is a MODIS image and lacks the clarity of the Landsat images.The main terminus of Sarqardliup Sermia has retreated 200 meters from 2000-2010 after exhibiting no trimline or significant retreat in the previous 50 years. The marginal changes of Sarqardliup Sermia as evidence by the lack of trimline are small compared to most areas around the Greenland Ice Sheet. As the ice sheet in the region thins at some point it will no longer dam Tiningnilik to the same level. Will the lake fill completely again this time? The 2010 fill limit was very close if not the same as previous levels, however, the seven year time for the refill was the fastest yet. Since this was not due to a lower level is this due to the record ice melting of the 2003-2010 period? There are two notable changes in the position of the terminus that ends in Tiningnilik at the green arrows from the 2000 to the 2010 image. There has been a 300 to 500 meter retreat of the terminus in these two locations and this could lead to greater calving and further retreat as this secondary terminus bed becomes deeper as it retreats toward the valley filled by the Sarqardliup Sermia. This would lower the outlet level of Tininglnilik, suggesting that the current refill will not be as high as previous lake fillings. The critical elevation is that of the bottom of the ice, the lower this is, the greater the hydrologic pressure for a given lake level and the lower the exit elevation is once a drainage path is established. In the intervening month melt rates have been high and the rate of infilling of Tiningnilik has been amazing as seen in the last image from July 14, 2012. To the south this has led to amazing flows in Watson River. <

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