After this frustration, Endurance‘s boilers were extinguished, committing the ship to drift with the ice until released naturally. On 17 February, the sun dipped below the horizon at midnight, showing the end of the Antarctic summer. On 24 February, regular watches on the ship were cancelled, with the Endurance now functioning as a shore station. The ship had slowly drifted south and at this point was within 60 mi (97 km) of the intended landing point at Vahsel Bay. But the icy terrain between the ship and the shore was too arduous to travel while carrying the materials and supplies needed for the overland expedition.
By March, navigational observation showed that the ship (and the mass of pack ice that contained her) was still moving, but now swinging towards the west-northwest and increasing in the speed of its drift, moving 130 mi (210 km) between the start of March and 2 May, when the sun disappeared below the horizon and the dark Antarctic winter began.
On 14 July 1915, Endurance was swept by a southwest gale, with wind speeds of 112 km/h (31 m/s; 70 mph), a barometer reading of 28.88 inHg (978 hPa) and temperatures falling to −33 °F (−36 °C). The blizzard continued until 16 July. This broke up the pack ice into smaller, individual floes, each of which began to move semi-independently under the force of the weather, while also clearing water in the north of the Weddell Sea. This provided a long fetch for the south-setting wind to blow over and then for the broken ice to pile up against itself while individual parts moved in different directions. This caused regions of intense localised pressure in the ice field. The ice began “working”, with sounds of breaking and colliding ice audible to those on the ship through the next day. Breaks in the ice were spotted but none approached the ice holding the Endurance.
During July the ship drifted a further 160 mi (260 km) to the north. On the morning of 1 August, a pressure wave passed through the floe holding the ship, lifting the 400-ton Endurance bodily upwards and heeling the ship sharply to her port side before she dropped into a pool of water, afloat again for the first time in nearly six months. The broken sections of floe closed in around the ship on all sides, jarring the Endurance forward, backwards and sideways in violent fashion against the other slabs of ice. After over a quarter of an hour, a force from astern pushed the ship’s bow up onto the floe, lifting the hull out of the pressure and with a list of five degrees to her port side. A gale overnight further disturbed the floe, driving it against the starboard side of the hull and forcing a sheet of ice upwards at a 45-degree angle until it reached the level of the scuppers. Despite the ordeal of the past few days, the ship remained undamaged.
Two pressure waves struck the ship on 29 August without incident. On the evening of 31 August, a slow-building pressure gripped the Endurance, causing her hull and timbers to creak and shudder continuously. The ice around the ship moved and broke throughout the night, battering the port side of the hull.[50] All was quiet again until the afternoon of 30 September, by which time there were signs of spring with ten hours of sunlight per day and occasional temperature readings above freezing. A large floe was swept against the Endurance‘s port bow and then gripped that side of the ship against the built-up ice and snow on her starboard beam. The ship’s structure groaned and wracked under the strain. Carpenter Harry McNish noted that the solid oak beams supporting the upper deck were being visibly bent “like a piece of cane”. On deck the ship’s masts were whipping back and forth as their stepping points on the keel were distorted. Despite these disconcerting signs, Worsley noted that the strength of the ship’s structure was causing the ice itself to break up as it piled against the hull—”just as it appears she can stand no more, the huge floe weighing possibly a million tons or more yields to our little ship by cracking across … and so relieves the pressure. The behaviour of our ship in the ice has been magnificent. Undoubtedly she is the finest little wooden vessel ever built”. Despite this, the ship’s decks were permanently buckled following this ordeal.
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