Natural Disasters are any natural occurrence that causes widespread distress, usually including loss of human life and notable damage to social system or property. They may cause large violent upheavals that usually impact a large number of people. They may cause large scale damage form which recovery is either impossible or long term. These included: avalanche, drought, dust storm, earthquake, fire, flood, hurricane (cyclone, typhoon), landslide, asteroid impact, monsoon, snow storm (blizzard), thunderstorm, tornado, tsunami, volcano, windstorm. In this unit we will discuss a few.
1980 - 2006 Billion Dollar U.S. Weather Disasters
(table available in print form)
www.ncdc.noaa.gov/loa/reports/billionz.html
Nor'easter
Liek a hurricane a nor'easter is counter -clock wise turning cyclone. Nor'easters are spawned by a very curvy Jet stream that dips far south allowing cold arctic air to meet warm air. The warm air rises over the cold, creating instability up high and an area of low pressure below. Once the system is formed, the earth's rotation causes the air to circle around the center (similar to when you drain the water out of your bath-tub). This creates the northeast wind, hence it's name nor'easter. They typically form near the Bahamas or north of Cuba, along the Appalachians or off Cape Hatteras.
The Jet Stream plays a very important role also in the strengthening of the storm. As the incoming air rises around the center, the Jet Stream moves it away further increasing the speed of the incoming air. The faster the air moves the faster the barometric pressure drops. Weather forecasters call a 24 mill bar drop in 24 hours "The Bomb". Normal Jet Stream winter pattern is to follow the coast and consequently drags the storm northeast ward. Some time a High Pressure zone further north blocks its path and so it churns over the ocean for a long time sending beach-eroding waves onshore. Also, warm water dragged up from ocean mixes with cold air from north causing lots of rain or snow. During the October to April nor'easter season February is the busiest month. Researchers say the biggest ones occur in October, January and March. What nor'easters don't achieve in wind-speed as compared to hurricanes, they achieve in duration (up to a week) and size (up to 1000 miles or more in diameter).(Nor easter, 2001)
Hurricanes
A hurricane is a type of tropical cyclone. The combinations of these conditions are needed for a Hurricane to form: 1) sea surface temperature has to be at least 20 degrees C / 80 degrees F., 2) unstable air that is warm and humid. 3) higher level winds that are weak and blowing in the same direction that the developing storm is moving. Tropical storm systems are classified as follows:
-
1. Tropical Depression - An organized system of clouds and thunderstorms with a defined circulation and maximum sustained winds of 38 mph or less.
-
2. Tropical Storm - An organized system of strong thunderstorm with a defined circulation and maximum sustained winds of 39 to 73 mph.
-
3. Tropical Cyclone or Hurricane - An intense tropical weather system with a well defined circulation and maximum sustained winds of 74 mph or higher. In the western Pacific, hurricanes are called "typhoons", and similar storms in the Indian Ocean are called "cyclones."
Hurricanes are products of the Tropical Ocean and atmosphere. They can develop when the sun's rays warm tropical waters heat to a least 82 degrees F, causing the air to grow warmer and rise. Water rises with it as vapor, and the heat causes the air to rise faster and faster. In several hours, the heated air will begin to circle counterclockwise, forming stronger and stornger winds that whirl with increasing speed. The moist, hot winds of a hurricane swirl upward around a calm column of low pressure air (the eye) it measures an average of 15 miles across. Inside the eye there are no storm clouds, almost no wind and calm conditions. The rising winds rotate around the eye, rising faster and fasster. When the hot air rises high enough it cools and form water droplets that cluster together as clouds and drop rain that is blown by harsh winds. Hurricanes are steered by the easterly trade winds and the temperate westerlies as well as by their own strong energy. Around their core, winds grow with great force, generating violent seas. As they move ashore, they sweep the ocean inward while spawning tornadoes and producing torrential rains and floods. Each year on average, ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, or Gulf of Mexico. Many of these remain over the ocean. (Abbott, 2006, 336- 339)
Tornadoes
A tornado is a powerful column of winds spiraling around a center of low atmospheric pressure. Three air masses, all moving different directions create conditions, giving spin to a thunder cloud. 1) A low - altitude northen flow of marine tropical air from the Gulf of Mexico that is humid and more than 72 degrees F. 2) Mid altitude, cold, dry air mass moving down from Canada or out from the Rocky Mountain at speed in excess of 50 mph. 3) And high altitude jet stream winds moving east more than 150 mph. The warmer air lifts vertically, releasing latent heat and forming a strong updraft that is spun at mid levels by fast moving polar air and and then twisted in another direction at its upper level by jet stream. The twisting motion is increased by vertical movement of warm air rising on the leading side and cool air descending on the trial side. It looks like a large black funnel hanging down from a storm cloud. The narrow end will move over the earth, whipping back and forth like a tail. The winds inside a twister can spin around at speeds up to 500 miles an hour, but usually travels at roughly 300 miles per hour. This makes the tornado the most dangerous storm known to mankind. Because of the earth's unique weather system, twisters rotate counterclockwise in the Northern Hemisphere and move eastward. They rotate clockwise in the Southern Hemisphere. Tornadoes also often come with hailstones. (Abbott, 2006, pg. 325)
Flooding
A flood is the submerging with water of a normally dry area. Floods are caused by many things, including rainstorms, slow water run -off, earthquakes, broken dams, underwater volcanic eruptions and tsunamis, or hurricanes.
During storms heavy rains fall for days and days, building up too much water for groundwater systems to handle. Slowly, the water levels begin to rise, creeping higher and higher until floods occur. In extremely bad cases, flash floods, with there rushing muddy water, sweep away houses, cars, trees, and people with ease.
Flash floods are much more dangerous and flow much faster than regular floods. They result from rapid / torrential rainfall during storms, dam failures, or excessive snow melts.
Heavy rains that come with Tropical storms are an example of one of the most common causes of floods. Such storms form over the warm water of the tropics, so they are full of moisture causing many inches of rain to fall. The heavy precipitation is too much for the streams and rivers to handle, causing water to overflow and produce inland floods. Many of these tropical storms form over the Gulf of Mexico.
Seasonal flooding can be caused by a variety of scenarios from heavy rainstorms, followed by heavy winter snow, then followed by unexpected heat waves in spring melting snow quickly and to flood rivers and tributaries.
Coastal flooding usually occurs as a result of severe storms, either tropical or winter storms. Ocean waves intensify and the storms make surface water choppier and stronger than normal. Raging winds can create huge waves that crash on unprotected beaches.
Coastal flooding can also be caused by long, low sea waves caused by volcanoes, melting ice, landslides, earthquakes, or explosion. These waves are called tsunami. These giant waves are difficult to detect on the open sea, so seismologist must keep track of earthquake movements that warn of possible tsunamis. These are extremely dangerous because of their high speeds. Deeper water means faster-traveling waves. When the sea floor is several miles below, waves can travel more than 600 miles an hour. As they near shallow water, they slow down, but build in height. Some tsunamis can be 50 to 100 feet high when they hit shore. (Abbott, 2006, pp. 372 - 382)
Droughts & Wild Fires
A drought occurs when there is not enough rain to support people or crops. In temperate regions, a drought is classified as 15 consecutive days with less than 0.01 inches of rain. During a drought, it still rains once in a while. However, storms or cloudburst are brief and any precipitation that falls dries up quickly afterwards. Small droughts occur every now and then, and these are not particularly harmful. Most happen in the summer, when hot and dry weather is normal. However, sometimes droughts can occur for months, years, or even decades.
When there is a dry spell, grass begins to turn brown. Flowers need to be watered more frequently. Dirt patches dry up. Cracks form across the surface of the ground. After many weeks of such weather, plants die out. The roots of the plants, which previously anchored soil down, can no longer keep the soil from eroding. The dirt is then blown up by the wind, causing huge clouds known as dust storms. Because they can turn the sky dark, they are sometimes known as black blizzards.
A wildfire has the devasting power to wipe away acres and acres of forest each year. Usually, forest fires occur in tropical rain forest and forest after dry spells. The dry needles of trees provide ideal fuel for wildfires, as well as the leaves of evergreen broad -leaved trees like holly, evergreen oak, and eucalyptus. In Australia, where eucalyptus grows in the bush (open forest land), bush fires are a common threat. (Lott, 2007)
