Download Geohazards Name: Period: Date: _____

Geohazards
Name: ______________________________________________________________________ Period: ____________________ Date: _______________
Essential Question: Where are the common locations of geohazards and how do they occur?
Geohazards can be defined as events related to the geological state and processes
that may cause loss of lives as well as material and environmental damages. These
geohazards arise from global geological processes inside the Earth, driving
deformation and displacement of its crust. Underneath the thin crust the Earth
consists of a sticky fluid of melted rock we call the mantle that undergoes convection
that turns and twists like boiling water, causing the crust to move.
The earth’s crust is divided in different plates called tectonic plates. When these plates
interact the resulting crustal movement can cause earthquakes, allow volcanoes to
erupt and set off landslides. All of these three; earthquakes, volcanic eruption and
landslides can trigger tsunamis if they happen in or close to the ocean. Earthquake,
volcanic eruption, landslide, tsunami, and sinkhole are all classified as geohazards.
Earthquakes: Earthquakes occur in plate boundaries or fractures on Earth’s crust
that can either be convergent, divergent, or transform. Earthquakes are caused by the
sudden release of accumulated strain along these faults, releasing energy in the form
seismic waves. A major earthquake is usually followed by aftershocks. Earthquakes
may cause liquefaction, landslides, and tsunamis. Most earthquakes happen along the
“Pacific Ring of Fire”, convergent boundaries around the Pacific Ocean.
Volcanoes: A volcano is an opening in the Earth's crust from which lava, ash, and hot
gases flow or are ejected during an eruption. Volcanic hazards vary from one volcano to
another and from one eruption to the next. The big killers of volcanic eruptions are
pyroclastic flows, lahars, and tsunamis triggered by volcanic eruptions. The most
frequent lethal events are so-called tephra explosions – very rapid jets of lava. The
Pacific Ocean is surrounded with hundreds of volcanoes earning the name “Pacific Ring of
Fire”.
Landslides: A landslide the breakup and downhill flow of rock, mud, water and
anything caught in the path. Landslides are one of the main processes by which
landscapes evolve and the related hazards result in a complex, changing landscape.
Extreme rainfall and earthquake can trigger a landslide. Landslides can happen on
slopes that are unprotected from erosion.
Tsunamis: Tsunamis are gravity waves (different physical features than wind
induced surface waves) created by a rapid displacement of a water column,
usually caused by an earthquake, volcanic eruption, and landslide on the ocean
floor . The displacement can be the result of earthquakes, volcanic eruptions or
landslides. These energetic waves travel fast in open ocean. When hitting
shallow water they build up to hundreds of meters high. The coastal inundation
or flood can be devastating and catastrophic.
Sinkholes are common where the rock below the land surface is limestone,
carbonate rock, salt beds, or rocks that can naturally be dissolved by
groundwater circulating through them. As the rock dissolves, spaces and
caverns called karst topography develop underground. Sinkholes are
dramatic because the land usually stays intact for a while until the
underground spaces just get too big. If there is not enough support for the
land above the spaces then a sudden collapse of the land surface can occur.
These collapses can be small or they can be huge and can occur where a house
or road is on top. The most damage from sinkholes tends to occur in Florida,
Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.
Clarifying Questions:
1. Define geohazard?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
2. What causes geohazards?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
3. What causes Earth’s crust to move?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
4. What are tectonic plates?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
5. How can tectonic plates result to earthquakes, volcanic eruption and landslides? Think!
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
6. What can trigger the occurrence of a tsunami?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
7. List the geohazards.
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
8. Where do earthquakes occur?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
9. List the three types of plate boundaries?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
10. Define seismic wave.
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
11. Define aftershock.
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
12. Why do aftershocks tend to cause more fatalities (deaths) than the main earthquake? Think!
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
13. Earthquakes can cause ______________________________________, ___________________________________, and ____________________________
14. Where do most earthquakes occur?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
15. What is a volcano?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
16. What are the big killers of volcanic eruption?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
17. What is a landslide?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
18. What causes the formation of a tsunami?
____________________________________________________________________________________________________________________________________________
____________________________________________________________________________________________________________________________________________
19. Sinkholes commonly happen in areas where the rock below ___________________________________________________________________
____________________________________________________________________________________________________________________________________________
20. In what states are sinkholes tend to happen frequently?
____________________________________________________________________________________________________________________________________________
R.E. Angat
Extreme geohazards
The Sumatran earthquake/Indian ocean tsunami was one of the most extreme geohazard in modern history (see list of
earthquakes). This extreme reached us all, beyond the mere geophysical waves. As tourists come from all over the world
to visit the beautiful shores of the Indian ocean, the 2004 tsunami affected people from around the globe. The extent of it's
destruction and the dimension of the disaster are parts of the definition of extreme. That, combined with their physical
features that normally are several orders higher or more powerful than the average geohazard. So, when we talk about
extreme geohazards we not only refer to the physical characteristics of the geohazard but also the risk they represent in
terms of consequences of this hazard.
DigitalGlobe’s Quickbird satellite captured an image of the devastation around Kalutara, Sri Lanka (top), on December 26,
2004, at 10:20 a.m. local time—about an hour after the first in the series of tsunami waves hit. Credit: DigitalGlobe
Chilean 1960 earthquake/tsunami is considered the largest – or most extreme – geohazard and natural disaster in modern
history. Since there were several warning foreshocks the earthquake itself did not take that many lives, but the tsunami
came as a surprise and in turn led to the construction of the Pacific tsunami early warning system.
The 7.8 magnitude earthquake in Tangshan, China, in 1976, is the most deadly earthquake ever recorded. The number of
deaths is however unclear (I've seen between 250 000 - 800 000) to date as the Chinese for political reasons towards the
end of the Cultural Revolution did not want to deal with the disaster other than saying that the disaster stricken would
and should rescue themselves etc.
Really extreme geohazards – megastunamis and supervolcanoes
Norway is situated in a safe distance from the Ring of Fire. Crustal movements in this part of the world are very slow
stemming from post glacial rebound, the uplift of ground due to the absence of heavy glaciers that melted thousands of
years ago. Norway has in fact a rather high number of earthquakes as well but these far from qualify as extreme
geohazards. But, if we look at the geological history of Norway we find evidence of a really extreme geohazard. More than
8000 years ago, the submarine Storegga landslide caused a wide ranging megatsunami hitting most of our entire coastline.
The dimension of both the Storegga slide itself and the resulting tsunami is almost incomprehensible. We cannot even begin to
think what damage such a tsunami would do to Norwegian oil industry, fisheries and our coastal population if it would have
taken place today.
Moving over the North Atlantic and almost to the West coast of the US in Wyoming, we find the beautiful Yellowstone
national park. Yellowstone is known for its wildlife and its many geothermal features such as geysirs. This park is namely
situated on the top of a vast calderas from several volcano eruptions so big that Yellowstone merits the name
supervolcano. Yellowstone is monitored by scientists that for obvious reasons find this place particularly interesting, and
they report that there are no signs that indicate the supervolcano is about to erupt any time soon.
Today Yellowstone seems like the most peaceful spot on the planet, but looking closer (and being a geoscientist) you'll find
evidence of a dramatic past. The Yellowstone supervolcano last erupted 650 000 years ago, the calderas covering an area of
55x 72 km.
There are several other fascinating geohazards of great dimensions such as Santorini in Greece, Lake Toba in Indonesia
and several others.
http://www.science20.com/planetbye/extreme_geohazards_what_are_they-85018
http://drpinna.com/earthquakes-and-global-warming-4026
http://mail.colonial.net/~hkaiter/volcanoes.html
http://volcanoes.usgs.gov/Imgs/Jpg/Landslide/30210600-077_caption.html
http://www.cartoonaday.com/japan-tsunami-cartoon-and-worse-things/
http://water.usgs.gov/edu/sinkholes.html