People and Planet - Naturally Hazardous

As citizens on Planet Earth, we are subject natural phenomenon over which we have little or no control.  Awesome in power, natural hazards can be local, such as wildfires, regional, such as droughts, or global, such as tsunamis.  

House damaged by the April 6, 2004 debris flow in Farmington, Utah.

Landslides are common natural hazards in Utah. They often strike without warning and can be destructive and costly. Common types of landslides in Utah are debris flows, slides, and rock falls. Many landslides are associated with rising ground-water levels due to rainfall, snowmelt, and landscape irrigation.  Therefore, landslides in Utah typically move during the months of March, April, and May, although debris flows associated with intense thunderstorm rainfall are common in July.



What causes the greatest damage in an earthquake?

This photo shows the Mission District of San Francisco burning after the 1906 earthquake. The greatest damage in earthquakes is usually not from the ground shaking. The greatest damage is caused by the effects of that shaking. In this earthquake, the shaking broke the gas mains and the water pipes. When the gas caught fire, there was no way to put it out. Fire causes the greatest damage in many earthquakes.

An earthquake is sudden ground movement. This movement is caused by the sudden release of the energy stored in rocks. An earthquake happens when so much stress builds up in the rocks that the rocks break. An earthquake’s energyis transmitted by seismic waves.

Almost all earthquakes occur at plate boundaries. All types of plate boundaries have earthquakes. Convection within the Earth causes the plates to move. As the plates move, stresses build. When the stresses build too much, the rocks break. The break releases the energy that was stored in the rocks. The sudden release of energy is an earthquake. During an earthquake the rocks usually move several centimeters. Rarely, they may move as much as a few meters

Floods are a natural part of the water cycle, but that doesn't make them any less terrifying. Put most simply, a flood is an overflow of water in one place. Floods usually occur when precipitation falls more quickly than water can be absorbed into the ground or carried away by rivers or streams. Waters may build up gradually over a period of weeks, when a long period of rainfall or snowmelt fills the ground with water and raises stream levels.

Extremely heavy rains across the Midwestern U.S. in April 2011 led to flooding of the rivers in the Mississippi River basin in May 2011.

April 14,2010                                              May 3, 2011

Record flow in the Ohio and Mississippi Rivers has to go somewhere. Normal spring river levels are shown in 2010. The flooded region in the image from May 3, 2011 is the New Madrid Floodway, where overflow water is meant to go. 2011 is the first time since 1927 that this floodway was used.

Flash Floods
Flash floods are sudden and unexpected, taking place when very intense rains fall over a very brief period (Figure below). A flash flood may do its damage miles from where the rain actually falls if the water travels far down a dry streambed.

A 2004 flash flood in England devastated two villages when 3-1/2 inches of rain fell in 60 minutes.

Droughts also depend on what is normal for a region. When a region gets significantly less precipitation than normal for an extended period of time, it is in drought. The Southern United States is experiencing an ongoing and prolonged drought. Drought has many consequences. When soil loses moisture it may blow away, as happened during the Dust Bowl in the United States in the 1930s. Forests may be lost, dust storms may become common, and wildlife are disturbed. Wildfires become much more common during times of drought.

Hurricanes—called typhoons in the Pacific—are also cyclones. They are cyclones that form in the tropics and so they are also called tropical cyclones. By any name, they are the most damaging storms on Earth.

Hurricanes arise in the tropical latitudes (between 10o and 25oN) in summer and autumn when sea surface temperature are 28oC (82oF) or higher. The warm seas create a large humid air mass. The warm air rises and forms a low pressure cell, known as a tropical depression. Thunderstorms materialize around the tropical depression. If the temperature reaches or exceeds 28oC (82oF), the air begins to rotate around the low pressure (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). As the air rises, water vapor condenses, releasing energy from latent heat. If wind shear is low, the storm builds into a hurricane within two to three days.

A cross-sectional view of a hurricane.

Hurricanes are huge and produce high winds. The exception is the relatively calm eye of the storm, where air is rising upward. Rainfall can be as high as 2.5 cm (1") per hour, resulting in about 20 billion metric tons of water released daily in a hurricane. The release of latent heat generates enormous amounts of energy, nearly the total annual electrical power consumption of the United States from one storm. Hurricanes can also generate tornadoes.  Hurricanes may cover 800 km (500 miles) in one day.

"Tsunami" is a Japanese word meaning "harbor wave." Some people call them tidal waves. But these deadly waves are not related to tides and they are not restricted to harbors. Few words can express the horror these waves can bring.

Tsunami are deadly ocean waves from the sharp jolt of an undersea earthquake. Less frequently, these waves can be generated by other shocks to the sea, like a meteorite impact. Fortunately, few undersea earthquakes, and even fewer meteorite impacts, generate tsunami.

Tsunami waves have small wave heights relative to their long wavelengths, so they are usually unnoticed at sea. When traveling up a slope onto a shoreline, the wave is pushed upward. As with wind waves, the speed of the bottom of the wave is slowed by friction. This causes the wavelength to decrease and the wave to become unstable. These factors can create an enormous and deadly wave.  Tsunami can travel at speeds of 800 kilometers per hour (500 miles per hour).

A video explanation of tsunami:

Natural hazards
There is a great source about natural hazards from UGS - contains a lot of great info specifically for Utah.

Source: Open Education Group Textbooks - Earth Science