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Lahars:One of the greatest volcanic hazards is lahars. Lahars are similar to
pyroclastic flows
but contain more water. Lahars form 1) from debris
avalanches that contain water from snow and ice which, when released,
mixes
with loose debris to form a lahar, 2) from pyroclastic flows and
surges which release water that mixes with debris, 3)
from pyroclastic
flows which dilute themselves with river water as they travel downslope,
4) from natural dam failure
(i.e. a lava flow dam or crater lake), and
5) from rainfall on loose material such as ash. Lahars that contain 20
to
60 percent sediment are usually very turbulent. Lahars that contain
greater than 80 percent sediment usually flow more
smoothly (laminar
flow). These smooth flowing lahars usually travel much faster than their
turbulent counterparts and
can float boulders, cars, buildings, and
bridges (Philippines, 1992).
Tornados: Tornaodos are nature’s most violent
storms. Tornadoes must always be taken seriously. Tornadoes can be very dangerous -- sometimes even deadly. They come from
powerful thunderstorms and appear as rotating, funnel-shaped clouds. Tornado winds can reach 300 miles per hour. They cause
damage when they touch down on the ground. They can damage an area one mile wide and 50 miles long. Every state is at some
risk, but states in "Tornado Alley" have the highest risk. Tornadoes can form any time of the year, but the season runs from
March to August. The ability to predict tornadoes is limited. Usually a community will have at least a few minutes warning.
The most important thing to do is TAKE SHELTER when a tornare nature’s most violent storms. Tornadoes must always be
taken seriously. Tornadoes can be very dangerous -- sometimes even deadly. They come from powerful thunderstorms and appear
as rotating, funnel-shaped clouds. Tornado winds can reach 300 miles per hour. They cause damage when they touch down on the
ground. They can damage an area one mile wide and 50 miles long. Every state is at some risk, but states in "Tornado Alley"
have the highest risk. Tornadoes can form any time of the year, but the season runs from March to August. The ability to predict
tornadoes is limited. Usually a community will have at least a few minutes warning. The most important thing to do is TAKE
SHELTER when a tornado is nearbyado is nearby.
Hurricanes: Hurricanes are severe tropical storms that form in the southern Atlantic Ocean, Caribbean
Sea, Gulf of Mexico, and in the eastern Pacific Ocean. Hurricanes gather heat and energy through contact with warm ocean waters.
Evaporation from the seawater increases their power.
Hurricanes rotate in a counter-clockwise direction around an "eye." Hurricanes have winds at least
74 miles per hour. When they come onto land, the heavy rain, strong winds and heavy waves can damage buildings, trees and
cars. The heavy waves are called a storm surge. Storm surges are very dangerous and a major reason why you MUST stay away
from the ocean during a hurricane warning or hurricane.
Avalanches have always occurred in the mountainous regions of the world though with the growth of winter-time
recreations, fatalities have been on the rise since the 1950s. Avalanches claim over 150 lives each year worldwide and hundreds
more are injured or trapped following an avalanche.
Ninety percent of all avalanches occur on moderate slopes with an angle of 30° to 45° (snow tends not
to accumulate on steeper slopes). Avalanches occur when the gravity pushing the collection of snow at the top of the slope
is greater than the strength of the snow itself. A change in temperature, a loud noise, or vibrations are all that are necessary
to trigger one of these snowfalls that begin at a "starting zone." The avalanche continues downslope along the "track" and
ultimately the avalanche fans out and settles in the "runout zone."
Internationally, the Alpine countries of France, Austria, Switzerland, and Italy experience the greatest
number of avalanches and loss of life annually
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