Natural Disaster Phenomena: Storms, Floods, and Landslides
Tornadoes: Formation and Impact
Tornadoes are violent storms that strike as a powerful, rotating mixture of wind and thunderstorm clouds, extending from the clouds to the ground in a funnel shape. They are known to be the most powerful and destructive atmospheric wind systems. They are very common in the USA, particularly across the middle belt extending to the East Coast.
When and How Tornadoes Form
Tornadoes usually occur during the daytime, typically from mid-afternoon until early evening. Their movement is generally from the southwest to the northeast, though they sometimes move in any direction, following the general path of the thunderstorm.
The most violent tornadoes originate from supercells—large thunderstorms that already have winds in rotation. Tornadoes form when warm, humid air collides with cold, dry air. The denser cold air is pushed over the warm air, usually producing thunderstorms. The warm air rises through the colder air, causing an updraft.
Sometimes tornadoes develop in a very short time frame, leaving very little lead time for warning and preparation.
Hurricanes: Tropical Storms and Their Effects
A hurricane is a large rotating storm with high-speed winds that forms over warm waters in tropical areas. Hurricanes have sustained winds of at least 74 miles per hour and feature an area of low air pressure in the center called the eye.
Hurricanes cause more damage to life and property than almost any other natural disaster. The effects of hurricanes include:
- Storm surges
- Strong winds
- Inland flooding
- Tornadoes
Determining the force of the hurricane helps predict the storm surge and the potential damage the storm can cause.
Impact on Communities and Warning Systems
Hurricanes affect people’s lives significantly due to the extensive damage they inflict. Winds can damage houses, trees, and any outdoor property. If the hurricane itself doesn’t destroy where people live, the major flooding that follows often will. When homes are destroyed, people may have to rebuild their homes and towns.
Warning systems provide crucial lead time:
- Hurricane Watches: Issued 24 to 36 hours before the expected landfall of the hurricane.
- Hurricane Warnings: Issued a few days in advance.
Additionally, if you observe heavy, stirring winds and very rough waters, there might be a hurricane approaching.
Floods: Causes and Consequences
A flood is an overflow of water onto land that is normally dry. It is a natural event where an area that is usually dry suddenly gets submerged under water. Floods can happen almost anywhere, covering an area with just a few inches of water or bringing enough water to cover the roof of a house. Floods can be dangerous for communities, lasting days, weeks, or sometimes even longer.
Types and Causes of Flooding
Some floods can occur suddenly and recede quickly (flash floods). Others take days or even months to build and discharge.
Severe flooding is primarily caused by:
- Atmospheric conditions that lead to heavy rain.
- The rapid melting of snow and ice.
Geography can also make an area more likely to flood. For example, areas near rivers and cities are often at risk for flash floods.
Impact of Flooding
When floods happen in populated areas, the water carries along objects, causing massive destruction. Floods can wipe away farms, trees, and many heavy items. Objects carried by the water include:
- Houses and bridges
- Cars and furniture
- Even people
Landslides: Mass Wasting Movement
A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. Landslides are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity.
Modes of Slope Movement
The term “landslide” encompasses five primary modes of slope movement. These are further subdivided by the type of geologic material (bedrock, debris, or earth):
- Falls
- Topples
- Slides
- Spreads
- Flows
Initiating Factors for Landslides
Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope exceed the strength of the earth materials that compose the slope. Causes include factors that increase the effects of down-slope forces and factors that contribute to low or reduced strength.
Landslides can be initiated in slopes already on the verge of movement by:
- Rainfall or snowmelt
- Changes in water level or stream erosion
- Changes in ground water
- Earthquakes or volcanic activity
- Disturbance by human activities
- Any combination of these factors