Engine 'explosions'... what causes them?

[andyofne]

Scenario

1991 Totoya Camry with 2.0l 4 cyl engine.
Oil changes July 07. Added oil two weeks ago as it seemed low.

Driving on interstate @ 70 (posted speed limit)

Engine bucks, car slows.

Engine explodes. Smoke, flame, bad noise.

Oil filter found on top of radiator when hood opened.

General question to the mechanically reclined:

What can cause an oil filter to be blown off the engine block?

Couldn't see what else was damaged at that point.

Engine still turned over so it did not seize but I sent it to the junk yard anyway.