ow is the formation of crevasses like the formation of icebergs? how do both form?

Answer 1

Crevasses form because of the movement of the ice in a glacier. The surface on which the glacier is moving is not smooth and flat, and although the ice in the glacier is slightly elastic, the bottom of the glacier moves at a diifferent speed from the upper layers (mainly becuase the bottom moves slower because of friction; but also if there are changes in slope). The differential movement causes the ice to crack, and form crevasses. You can see a similar effect if you try to bend a slice if cake - the upper surface will crack across.
Many crevasses are transverse (running across the glacier), because they form at right angles to the direction of mevement; but others form logitudinally, especially nearer the edges of the glacier, where the sides move slower than the centre. If the glacier passes over a very steep slope or cliff, an 'ice fall' will form, where the whole glacier will be broken up into irregular shapes ('seracs').
There is also a special type of crevasse called a bergschrund, which forms at the head of the glacier, where it leaves the basin in which it formed (the 'neve field').
The crevasses are not necessarily permanent, and may close again if the ice moves together; or new crevasses may form lower down the slope.

When the glacier reaches its destination (if it reaches the sea or a lake), parts of the glacier will break off and float away as icebergs. Naturally, the weakest sections will be where the crevasses are, so it is most likely to break ('calve') there; but not always so.