450 NANSEN — POLAR EXPEDITION, 1893-96. [Oct. 29, 



By the pressures the ice is, however, piled up to very much 

 greater thicknesses, and ridges and hummocks are formed, the 

 height of which may amount to twenty feet or even more above 

 the water. The highest hummock I ever measured was twenty- 

 three feet high, so far as I remember. I saw a few which 1 esti- 

 mated to be about thirty feet high. These hummocks will freeze 

 solid and will last for years. I might mention one which was 

 formed near the Fram in January of our first year, which followed 

 the Fram during the whole time of the drift. This hummock has 

 probably drifted on southward along the East Greenland coast. 

 The ice floes are crushed easily, but these hummocks require much 

 more force to crush them. They will stay together and be the last 

 remnants of the ice to be carried around Cape Farewell and the 

 west coast of Greenland. 



The cause of these ice pressures has already been referred to in 

 the accounts of previous expeditions. It is a fact, which has often 

 been observed by various explorers, that the pressures are to some 

 extent caused by the tidal currents. Our observations showed that 

 at the margins, near the outer edge of the polar ice-pack, where 

 there is an open sea to the south, the ice pressure is almost solely 

 caused by the tidal currents. The pressures were there often so 

 regular in their occurrence that we could say beforehand when the 

 ice pressures would occur. We knew that they would come with 

 the spring tide, the heaviest ones a little after new moon, and 

 another period with less heavier pressures about full moon. The 

 pressures would at these periods generally occur twice in twenty- 

 four hours. Then the ship would often be lifted a good many 

 feet out of the water, while in the intervals the openings in the ice 

 would widen out and the ship would be floating in a broad, open 

 channel. 



In the interior of the polar ice these tidal currents do not seem 

 to have much influence on the pressures. I could not discover any 

 regularity in them there. The pressures seemed to be caused 

 mostly by the changing winds. It is evident that when the wind 

 suddenly changes, especially to the opposite direction to that from 

 which it has been blowing for some time, immense pressures must 

 arise. The great body of ice is moving on, while in front the ice is 

 moving against it. We had a very severe nip on such an oc- 

 casion about New Year's day, 1895. I dare say it was the heavi- 

 est ice pressure any ship has ever been exposed to, and that was 



