In 1959,the Water Stored Behind Hegben Lake Dam in Montana

In 1959,the water stored behind Hegben Lake Dam in Montana began to slosh violently back and forth in a series of oscillating waves.These seiches were caused by __________________.

A) the collapse of the dam
B) a large landslide into the lake
C) a small meteor crashing into the lake
D) a freight train plunging off a track and into the lake
E) a sudden drop of the lake bottom during an earthquake