Ice Relaxation
Deep ice is under great pressure. When brought to the surface, there is a drastic change in pressure. Due to the internal pressure and varying composition, particularly bubbles, sometimes cores are very brittle and can break or shatter during handling. At Dome C, the first 1000 m were brittle ice. Siple dome encountered it from 400 to 1000 m. It has been found that allowing ice cores to rest for some time (sometimes for a year) makes them become much less brittle.
Decompression causes significant volume expansion (called relaxation) due to microcracking and the exsolving of enclathratized gases. Relaxation may last for months. During this time, ice cores are stored below -10 °C to prevent cracking due to expansion at higher temperatures. At drilling sites, a relaxation area is often built within existing ice at a depth which allows ice core storage at temperatures below -20 °C.
It has been observed that the internal structure of ice undergoes distinct changes during relaxation. Changes include much more pronounced cloudy bands and much higher density of "white patches" and bubbles.
Several techniques have been examined. Cores obtained by hot water drilling at Siple Dome in 1997–1998 underwent appreciably more relaxation than cores obtained with the PICO electro-mechanical drill. In addition, the fact that cores were allowed to remain at the surface at elevated temperature for several days likely promoted the onset of rapid relaxation.
Read more about this topic: Ice Core
Famous quotes containing the words ice and/or relaxation:
“Every incident connected with the breaking up of the rivers and ponds and the settling of the weather is particularly interesting to us who live in a climate of so great extremes. When the warmer days come, they who dwell near the river hear the ice crack at night with a startling whoop as loud as artillery, as if its icy fetters were rent from end to end, and within a few days see it rapidly going out. So the alligator comes out of the mud with quakings of the earth.”
—Henry David Thoreau (1817–1862)
“Worst of all, there is no sign of any relaxation of antisemitism. Logically it has nothing to do with Fascism. But the human race is imitative rather than logical; and as Fascism spreads antisemitism spreads.”
—George Bernard Shaw (1856–1950)