Geology Reference
In-Depth Information
people attempt to drive through pools of standing water, not realizing how deep it
really is until it's too late.
Caving In: Sinkholes
Sinkholes occur when groundwater erodes underground rock, removing the bedrock ma-
terial that is supporting the land surface, so that the soil, sediment, and any structures
built on it collapse. Sinkholes can occur anywhere that the underlying rocks have water-
soluble minerals in them and are most common in regions with karst topography (which
I describe in Chapter 12). In such regions, the underground erosion creates caves and
cavities beneath the surface, so there's not enough material to support the land surface
above.
Sinkholes often cave in right after a heavy rainfall; the added weight of the water in the
soil is too heavy for the roof of the underground cavity to support, and it collapses.
When a sinkhole forms, collapsing inward, it leaves a funnel-shaped depression on the
ground surface. Anything on that surface sinks into the hole, including roads, bridges,
buildings, and homes.
Sliding Down: Landslides
Landslides are a type of mass wasting (see Chapter 11) where large amounts of rock and
soil move downslope rapidly. They are most hazardous in populated and developed re-
gions, where they may destroy homes or block roads.
Landslide conditions are created under a number of different circumstances that result
in unstable slopes — where the materials on the slope cannot be supported, and
everything slides down. The potential for a landslide increases when heavy storms bring
rain that adds weight to the land surface or when earth-shaking events such as earth-
quakes or volcanoes occur. Landslide conditions can also be created by erosion (a topic
I discuss later in this chapter).
Shaking Things Up: Earthquakes
Earthquakes occur all over the planet all the time. But they become geologic hazards
when they occur near the surface, are particularly strong, or happen in regions that are
