Do they explode because they are exposed to external pressure above the limit? Yes. Because the mechanism is affected in some other way to think the pressure is high enough? No. Waves relevant? No. Sea creatures? No. Other natural causes? No. Manmade causes? For SVV of "manmade causes." Is the danger that when a destroyer sinks, all depth bombs go off at once, posing a danger to nearby ships? Why do they all go off at once?
There are three dangers of depth charges to the ships that carry them. Two you've found:
1. When hit, the explosives go off just like a magazine, destroying the entire ship.
2. The ship is too slow to escape the explosion of its own charges after dropping them.