In a new study, Northeastern earth and environmental sciences professor Jennifer Cole has discussed what causes earthquakes and how one natural disaster can lead to another. As to what causes earthquakes, Cole says that they result from the movement of tectonic plates.

As tectonic plates slide past each other, energy builds up in the rocks until they can no longer hold the stress. This causes failure in the form of breaking rocks, sending energy waves outward. The earthquakes in Haiti, China, Japan, and Chile all happened because of this series of events.

Glaciers may also cause earthquakes. During the last glacial period, the ice sheet was up to 2.5 miles thick. This pushed down on the Earth's crust, causing a depression. When the weight was lifted due to glacial melting, the depressed crust began to stick-slip on its way back to the pre-depressed elevation.

In addition, humans can cause earthquakes by damming rivers, creating a reservoir heavy enough to cause a depression in the earth's crust. A massive earthquake is usually followed by a sequence of aftershocks, landslides and tsunamis.

Earthquakes are capable of causing tsunamis. In the unique case when an earthquake occurs on the ocean floor, a rock is forced up, causing a disturbance in the water column that extends to the ocean surface. Waves then travel outward in a series of concentric circles at a rapid rate, up to 550 miles per hour, or as fast as a jet airplane travels.

When tsunamis reach shallow water, they slow down and grow taller, forming massive waves. These waves travel inland and cause flooding and increase the potential of coastal landslides. Some scientists are making the case that global warming is contributing to an increase in earthquake activity by making the ocean water warmer, and therefore, heavier. Additionally, melting glaciers take weight off of tectonic plates, which can cause them to pop upwards in those areas, resulting in earthquakes.