A large landslide can trigger a tsunami that can have devastating effects.
Examples:
(1) Lituya Bay, Alaska, 1958
(2) Vajont Valley, northern Italy, 1963
These tsunamis have the potential of causing extremely high waves hundreds of feet high.
The magnitude depends on:
(1) the mass of the landslide
(2) the speed at which it occurs
Risk factors for occurrence:
(1) unstable mountain
(2) large drop with a steep angle
(3) large body of water at the bottom
(4) triggering event such as earthquake or heavy rains
These can occur in:
(1) lakes, including man-made reservoirs
(2) bays or inlets
(3) underwater (submarine)