It frequently happens that two masses are propelled against each other, and are both shivered into fragments by the violence of the concussion.  The ordinary swell of the ocean also acts with tremendous power upon a large tract, especially when it has been so thawed as to have become thin, and breaks it up into a thousand smaller pieces in a very short period.  The danger of being entrapped between two ice-fields coming into contact with each other is one of the perils which the navigator has frequently to encounter in the northern seas; and fatal to his vessel and his life has the occurrence often been, while in a vast number of instances escape has seemed almost miraculous.

“At half-past six,” says Captain Ross, relating to his first voyage of discovery, in the Isabella, to the arctic regions, with Captain Parry, in the Alexander, “the ice began to move, and, the wind increasing to a gale, the only chance left for us was to endeavor to force the ship through it to the north, where it partially opened; but the channel was so much obstructed by heavy fragments, that our utmost efforts were ineffectual; the ice closed in upon us, and at noon we felt its pressure most severely.  A large floe, which lay on one side of the Isabella, appeared to be fixed; while, on the other side, another of considerable bulk was passing along with a rapid motion, assuming a somewhat circular direction, in consequence of one side having struck on the fixed field.  The pressure continuing to increase, it became doubtful whether the ship would be able to sustain it; every support threatened to give way, the beams in the hold began to bend, and the iron tanks settled together.

“At this critical moment, when it seemed impossible for us to bear the accumulating pressure much longer, the hull rose several feet; while the ice, which was more than six feet thick, broke against the sides, curling back on itself.  The great stress now fell upon our bow; and, after being again lifted up, we were carried with great violence towards the Alexander which had hitherto been, in a great measure, defended by the Isabella.  Every effort to avoid their getting foul of each other failed; the ice-anchors and cables broke one after another; and the sterns of the two ships came so violently into contact, as to crush to pieces a boat that could not be removed in time.  The collision was tremendous, the anchors and chain-plates being broken, and nothing less than the loss of the masts expected; but at this eventful instant, by the interposition of Providence, the force of the ice seemed exhausted; the two fields suddenly receded, and we passed the Alexander with comparatively little damage.  A clear channel soon after opened, and we ran into a pool, thus escaping the immediate danger; but the fall of snow being very heavy, our situation still remained doubtful, nor could we conjecture whether we were yet in a place of safety.  Neither the masters, the mates, nor those men who had been all their lives in the Greenland service, had ever experienced such imminent peril; and they declared, that a common whaler must have been crushed to atoms.”