They are more apt to break up in warm weather than in cold, and whalers and sealers note this before landing on them when an anchor is to be planted or fresh water to be obtained.
On the coast of Labrador, in July and August, when it is packed with bergs, the noise of rupture is often deafening, and those experienced in ice give them a wide berth.
When they are frozen the temperature is very low, so that when their surface is exposed to a thawing temperature the tension of the exterior and interior is very different, making them not unlike a Prince Rupert's drop.
Then, too, during the day, the water made by melting finds its way into the crevices, freezes, and hence expands, and, acting like a wedge, forces the berg into fragments.
Much of the ice encountered at sea is discolored, and often full of dirt and gravel, while not infrequently stones are found imbedded in it.
Along the shores of Labrador, where there is a large rise and fall in the tide, ice is brought into contact with the bottom, and mud and sea-weed are frozen in with it, while at times landslides precipitate large quantities of dirt and stones on its surface.
As the ice leaves the coast and comes to the southward, it brings these burdens with it, which are deposited on the ocean bottom when the ice melts. As this melting occurs to a great extent over the Grand Banks, it would seem that the deposit from the field ice would be greater than that from bergs.
It is hard to understand why bergs should have foreign substances frozen into them, as they are formed from snow deposited on the frozen surfaces in the interior of Greenland, and hence their thickness is added to from their upper surface.
It is possible that in their journey south in the Arctic current they accumulate more or less foreign matter by having it ground into their bottoms; but this does not seem probable, as it is hard to force gravel into ice and give it a permanent hold, while mud accumulated in this way would soon be washed out.
Then, too, the largest bergs find their way around the edges of the Banks, and do not cross, on account of their draught, for only an average-size berg crosses the Banks.