A volcano caldera is a depression in the ground created by the collapse
of land after a volcanic eruption. In some cases, the caldera is created
slowly, when the ground sinks down after a magma chamber is emptied. In
other situations, the magma explodes violently, and the caldera is the
deep pit in the ground that remains after the volcano blows its top off.
http://www.universetoday.com/31160/volcano-caldera/Animation of how a caldera forms: http://www.bioygeo.info/Animaciones/Caldera.swf
Here we can see the oceanic plate moving from left to right. The top layer
of the mantle and the crust (all called the lithosphere) sinks beneath the continent.
A deep ocean trench is formed. Water gets carried down with the oceanic crust
and the rocks begin to heat up as they travel slowly into the earth. Water is
then driven off triggering the formation of pools of molten rock which slowly
rises. The plate moves downwards at a rate of a few centimetres per year. The
molten rock can take tens of thousands of years to then either:
- Solidify slowly underground as intrusive igneous rock such as
granite.
or
- Reach the surface and erupt as lava flows. Cooling rapidly to form extrusive igneous rock such as basalt.
The floor of the Easter Pacific is moving towards South America at a rate of
9 centimetres per year. It might not seem much but over the past 10 million years
the Pacific crust has been subducted under South America and has sunk nearly 1000
kilometres into the Earth's interior.
As the rift valley expands two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does.
As the rift valley expands, water collects forming a sea. The Mid-Atlantic Ridge is now 2,000 metres above the adjacent sea floor, which is at a depth of about 6,000 metres below sea level. The sea floor continues to spread and the plates get bigger and bigger. This process can be seen all over the world and produces about 17 square kilometres of new plate every year.
http://www.moorlandschool.co.uk/earth/tectonic.htm
Animation : http://www.bioygeo.info/Animaciones/DivergentBoundary.swf
En la imagen de arriba se precia como los océanos pueden cerrarse al
colisionar la corteza continental de ambas orillas, movida por una
Dorsal mas potente, dando lugar a la colisión de placas continentales y
al crecimiento de los contimentes. Parecido proceso hizo colisonar a la
India con Asia, originando la cordillera del Himalaya. (Imagen del
libro "continentes en colisión" de la colección Planeta Tierra de
Time-Life)
Millions of years ago India and an ancient ocean called the Tethys Ocean were sat on a tectonic plate. This plate was moving northwards towards Asia at a rate of 10 centimetres per year. The Tethys oceanic crust was being subducted under the Asian Continent. The ocean got progressively smaller until about 55 milion years ago when India 'hit' Asia. There was no more ocean left to lubricate the subduction and so the plates welled up to form the High Plateau of Tibet and the Himalayan Mountains. The continental crust under Tibet is over 70 kilometres thick. North of Katmandu, the capital of Nepal, is a deep gorge in the Himalayas. the rock here is made of schist and granite with contorted and folded layers of marine sediments which were deposited by the Tethys ocean over 60 million years ago.
http://www.laalianzadegaia.com/obduccion.html
http://www.moorlandschool.co.uk/earth/tectonic.htm
Animation of the same process: http://www.bioygeo.info/Animaciones/Foliation1.swf
Animation (formation of the Himalayas): http://www.bioygeo.info/Animaciones/ConvergentMargin.swf
Animation (three types of boundaries): http://www.bioygeo.info/Animaciones/PlateMotion.swf
http://volcano.oregonstate.edu/hot-spot-volcanism
A hotspot is a region of high volcanic activity not located at a tectonic plate boundary.
It is caused by upwelling of deep mantle plumes.
Hotspots are 100 to 200 km across.
Hawaii is the best known example of hotspot volcanism. The mantle plumes are long lived and relatively stable.
As an area moves over the plume new volcanoes form producing a chain of volcanoes.
Hotspots are irregularly distributed over half the world's surface and estimates of their total number varies from 42 to 117.
Activity:
Who was Marie Tharp?What thecnology did she use to make her map?
What later thecnology proved Tharp’s map to be accurate?
Are the oceanic crust denser than the continental one because the weight of the water or because the rocks in each crust are different?
Have the scientists ever touched the sea floor? If so, was it before or after they touched the Moon?
http://www.earthinstitute.columbia.edu/news/images/TharpMapLarge.jpg
http://c250.columbia.edu/c250_celebrates/remarkable_columbians/marie_tharp.html
http://www.marine-geo.org/portals/gmrt/
http://www.laalianzadegaia.com/corteza_terrestre.html
Faults and folds: http://ees.as.uky.edu/sites/default/files/elearning/module10swf.swf
What are the effects of an earthquake?
Animation: earthquakes effects (choose "model"): http://ees.as.uky.edu/sites/default/files/elearning/module11swf.swf
Virtual volcano (choose "build your own volcano and watch it erupt"): http://dsc.discovery.com/convergence/pompeii/interactive/interactive.html
Earthquakes from around the world in last 24 hours : http://www.mibazaar.com/earthquakes.html
Last earthquakes in Spain: http://www.ign.es/ign/layout/sismo.do
Good, and short, National Geographic videos:
- Earthquake 101: When the trembling stops, the disaster is only the beginning.
Volcano Eruptions: Watch spewing volcanoes, descending lava, and a truck try to escape a lava trap.
Volcano Lava: Get immersed in a volcanic landscape with bubbling lava, spewing eruptions, and colliding rivers of fire.
Ultimate Volcano: Naples faces a potential super eruption.
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