Witnessing time - from 445 million year old rocks exposed in the Fjords to ~4 thousand year old small ice caps
By Hakim Abdi, LDEO.
My first flight on the P3 and the scenery was nothing short of breathtaking. The science mission involved flights in the north over the Steensby glacier that passes through Sherard Osbron Fjord, and Ryder glacier constrained by the Victoria Fjord. In northeast Greenland we overflew the Hagen glacier and the Flade Isblink Ice Cap in Kronprins Christian Land.
The sheer dimensions of the fjord cliffs on the northern flights were striking. In north Greenland they were quite steep, at almost 90 degrees, and appeared to be carved with surgical precision. Formed in the last glacial period as Greenland was covered with ice and snow, the weight of the ice depressed the crust and glaciers cut through surrounding rock. Since the end of the last ice age, a phenomenon called ‘crustal rebound’ has taken place. The formerly depressed land masses have slowly risen in a process is called isostasy, resulting in these awe-inspiring cliffs.
Outside the scientific community, glaciers are sometimes thought of as ‘just a block of ice’, but they are much like landmasses in their own right, close to inland islands. They are solid, yet they are dynamic, with internal layers that record events during the lengthy history of their formation. They also have surficial features, including crevasses, such as those shown below. Crevasses are deep cracks in the ice sheet, equivalent to fractures in rock, and are formed due to a combination of factors including differences in the ice speed between the edges and center of the glacier, stresses generated by flow over an uneven terrain, and the stress created from the glacier’s lower layers being more malleable than its upper layers.
In Northeast Greenland we focused on the Hagen glacier and the Flade Isblink icecap. Like the flights over the northern glaciers we are resurveying historical ATM lines. Flade Isblink is a small, ~600 m thick, icecap in the furthermost northeast corner of Greenland located just south of Station Nord (a permanently occupied Danish scientific and military base) in Kronprins Christian Land. Flade Isblink faces the Polar Ocean and is separated from the central ice sheet so the age of the ice in this small icecap was recently determined to be much younger than the main icesheet. An ice core drilled by the Centre for Ice and Climate, Copenhagen University, suggests the age of this small ice cap to be between 2800 -4000 yrs (A. Lemark, 2010).