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 , allow volcanoes to erupt and set off . All of these three; earthquakes, volcanic eruption and landslides can trigger if they happen in or close to the ocean. , volcanic eruption, , , and 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 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, , 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 .

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 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. 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 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 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