Geology Reference
In-Depth Information
Chapter 24
Ten Geologic Hazards
In This Chapter
Learning more about familiar geologic dangers
Identifying less common hazards
Living on earth can be dangerous. Earth is a dynamic planet, geologic processes are al-
ways in motion, and while some processes take millions of years (like the formation of a
sedimentary rock), others happen very quickly (like a volcanic eruption). All these pro-
cesses are natural, but they become hazards when they affect human lives and the infra-
structure of modern society. In this chapter, I describe some common and not-so-com-
mon geologic hazards.
Changing Course: River Flooding
All over the world water flows from higher elevations to lower elevations as stream or
river flow. The movement of water through a region over a long period of time carves out
riverbeds and stream channels. But rivers don't always stay in the same place. Under the
right conditions, they may change course or overflow their banks, resulting in a flood.
Floods are caused by many factors, but the bottom line is that there is too much water in
one place at one time and the streamflow of the river can't move it downstream quickly
enough. This event is very common in the springtime, as rainfall melts snow and over-
loads the stream channels with water. As the water spills over the banks of the river
channel, whole towns may find themselves inundated.
Lives lost to flooding are often the result of
flash flooding
— when rainfall oc-
curs so quickly and heavily that there is no warning before water comes rushing
across roadways and taking out bridges. Drivers and their vehicles may be swept
away in a current of flood water. Another dangerous situation during floods is when
