Chapter 1: Hazards and Disasters: Important Concepts

Slow, day-to-day geologic processes and hazardous events are a result of energy being transferred in the Earth system. Geologic processes occur continuously. Slow continuous geologic processes occur all the time. Some examples:

• Rivers flow and erode the landscape.

• Moving plates slowly raise mountains.

• Continents slowly drift over the face of the Earth.

• Sedimentary rocks are slowly deposited in the oceans.

These and many other processes can, over great periods of time, dramatically change the Earth's surface. The idea of continuous change over great expanses of time is known as uniformitarianism.

Change is driven by energy. Geologists distinguish between two important energy sources:

Internal energy: Heat energy being released from the interior of the Earth.

1. Drives plate tectonics, resulting in

2. earthquakes,

3. tsunamis,

4. volcanoes.

External energy: Heat energy from the sun, drives weather related events;

1. Floods

2. Severe weather (Hurricanes, tornadoes, etc).

Slow geologic processes occur continuously (uniformitarianism). Occasionally, energy is concentrated in a part of the geologic environment. When energy is suddenly released, a hazardous event may result.

Hazardous events are rare. Lucky for us, the larger the event, the rarer the event; the more energt is released, the lower the frequency is the event. Low energy events are common and happen every day. High energy, hazardous events are rare and infrequent.