Chilean
Earthquake…Wednesday September 16, 2015
The west coast of the United States
main land and Hawaii had tsunami alerts posted after the quake near Coquimbo,
Chile Wednesday morning. This quake was
determined to be an 8.3 on the Richter Scale.
In an article from the (Tsunami Alarm System) web site it was stated that the quake’s energy had
to be at least 7.0 on the Richter Scale.
From Australian Geographic in an article entitled (“Tsunamis: how they form”) Professor Dale Dominey-Howes, co-director of
the Australian Tsunami Research and Natural Hazards Research Centre at UNSW
stated “ Broadly speaking earthquakes have to be a magnitude 6 or above to
trigger a tsunami, and the closer to the sea floor an earthquake is the more
likely it is to generate a tsunami.” Professor also said that while regular ocean
waves have a wavelength (distance from wave crest to wave crest) of 30 to 40
meters, tsunami wavelengths can be from 100 to 200 kilometers. These waves could arrive on shore anywhere from
ten minutes to nearly an hour apart. In
miles this is from 62 miles to 124 miles. (Fact
Monster)
Now how is a tsunami formed? On the ocean floor where fault lines form at
plate boundaries you will have two types of boundaries. A convergent boundary is when plates move
toward each other. The older and denser
crust will be subducted (go under) the other plate where they meet. This is called a subduction zone. At the subduction zone the older denser plate
will slowly bend the leading edge of the younger, less dense plate. Crustal rock (rock in the crust of the Earth)
has a property called elastic rebound.
Which means the crustal rock is like a stretched rubber band. It wants to snap back to its original shape. At the fault line after a very long period of
time the friction between the two plates, grinding past each other, will no
longer be able to stop the younger, less dense plate from rising back up to its
original position. This is when an
earthquake happens. As the sea floor
rises up to its original position the water above the quake will be pushed
up. Remember unlike gases, liquids
cannot be compressed. As in the
earthquake off Indonesia in 2004, the water rose by 10 meters/ 30 feet. Next the raised dome of water creates waves
that started moving away from each other in opposite directions. In Lindsey
Springer’s (springle@uwec.edu) article the tsunami wave
in deep ocean moves at speeds from 450-650 mph and the wave is only 20 inches
tall. In other words boats would not
even noticed it passed by. As the wave
approaches a coastline the leading edge slows down due to friction with the
rising sea floor. As the leading edge
slows the rest of the wave behind still moving at speeds of 30 to 200 mph. Thus the large waves are formed. Lindsey also reported that the waves can be
as high as 100 feet or more, and the wave from front to back could be from
5,000 to 10, 000 feet. Imagine a wave 100
feet high and nearly two miles size from the front of the wave to the back of
the wave. This wave just does not wave
up on the shore and recede quickly. The
tsunami wave will continue to push in land for miles taking everything with it.
http://observe.arc.nasa/exhibits/tsunami/tsun_physics.html
Other ways
tsunamis can be formed are: volcanic eruptions, huge landslides into the ocean,
and even meteor or asteroid impacts. In
1883 the Krakatoa Volcano off the coast of Sumatra, Indonesia blew itself apart
in a massive explosion that created a tsunami wave that was 120 feet tall when
it struck the surrounding islands. Over
33,000 people died.
There is a volcanic mountain in
Canary Islands off the west coast of Africa.
Scientists are stating that one day a massive chunk of rock, some 220
square miles, in an eruption of the Cumbre Vieja volcano on La Palma Island will
crash into the Atlantic Ocean creating a tsunami wave that would be the biggest
ever. (Steve Connor: The Independent-London) In Connor’s article “Scientists Warn of
Massive Tidal Wave from Canary Island Volcano”, he writes that the resulting
wave could be as high as 169 feet as it crashes into eastern seaboard of
America, Brazil, and inundate much of southern Britain. (Rense.com/general13/tidal.htm)
(http://news.independent.co.uk/world/africa/story.jsp?)
But other geologists are even saying that
this 220 square mile chunk of the volcano will slide into the ocean as a result
water erosion in the mountain and the force of gravity.
There is also disagreement of
whether or not a tsunami wave of such great size would even reach the east
coast of the United States. These
scientists say that a tsunami created by a landslide from an exploding volcano
would be short-lived with there being little or no waves that reach the east
coast. The tsunami wave created by the
explosion of Krakatoa Volcano in 1883 was over 100 feet high but there were no
reports of damage outside areas of Indonesia.
While the 2004 earthquake-created tsunami in Indonesia affected large
areas as far away as Africa; killing nearly 300,000 people along the coastlines
of nearby countries.
So only time will tell who is
correct. But all do agree it will happen,
but no one knows when. Scientists are
calling for better monitoring the volcano’s activity to warn of possible
danger, and give countries enough time to get people out of the way of the
tsunami.
Sources,
Follow-up links:
Information
about terms, causes, characteristics, occurrences, prevention and list of past
tsunamis (www.en.wikipedia.org)
Behavior in
case of a tsunami (http://gfz-potsdam.de/index-en.html
Academic.evergreen.edu/g/grossmaz/springle
Rense.com/general13/tidal.htm
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