What is the relationship between the plates and earthquakes and volcanoes?

4 comments

1. 

   Earth Man on July 15, 2010 at 5:13 pm

   So your question basically, is, "Explain plate tectonics."

   Earthquakes (the vast majority of them) occur at plate boundaries. Most of the time, all you need is a large amount of rock, under large forces, moving past each other. The rock deforms under the stress, and when it can’t handle further stress, it snaps back to where it "should" be, in what is called elastic rebound. This is an earthquake.

   The most frequent, and moderate-sized quakes occur at transform boundaries (*not* passive boundaries), where two plates move past each other along a horizontal plane. Example, the Pacific plate moving north relative to the North American plate moving south along the San Andreas Fault Zone.

   The largest earthquakes, but infrequent, occur at convergent boundaries, where to plates are meeting in a collision (doesn’t matter if there’s subduction or not). Example, as a non-subduction type, the large earthquakes near the Himalaya Plateau, where the Indo-Australian and Eurasian plates are meeting on a north-south collision. Example, as a subduction-type meeting, the Nazca plate moving east and subducting beneath the South American plate moving west. The largest earthquake on record, the 1960 Chile earthquake occurred here, a 9.5, associated with the Peru-Chile Trench.

   The actual most frequent, but very small earthquakes occur along divergent boundaries, basically the Mid-Ocean Ridge, where plates are moving apart. You have many, many, many, small, small earthquakes as magma rises to either fill in a vacancy, or to push plates apart, causing rock to grind together as an earthquake. Nobody but geologists care about them. Exception — Icelanders, because the Mid-Ocean Ridge comes on land and bisects their island. They got lots of fairly good-sized quakes. So, example, North American plate moving west, Eurasian plate moving east, away from the Mid-Atlantic Ridge.

   One interesting exception to the tectonic boundary rule are the intra-plate earthquakes. These can take place *anywhere* and are caused by huge compressional forces from the tectonic boundaries that have been transmitted through the crust. Generally this will reach a zone of existing weakness to create an earthquake, such as the New Madrid Fault Zone in Missouri. But sometimes? They just happen wherever the hell they want to happen. When they do happen, they’re usually moderately-large, such as the one that happened a week ago up in Ontario, Canada (this happened along an existing zone of weakness).

   Volcanoes are related with convergent and divergent boundaries, but *not* with transform boundaries.

   The divergent boundaries (the Mid-Ocean Ridge) as stated, are where magma is constantly rising and being erupted as new surface crust. This by definition, is is a volcano. Just a small one (again, unless you happen to live in Iceland).

   Convergent boundaries of subduction-style, either oceanic-oceanic or oceanic-continental crust collisions will have the subducting plate eventually reach a melting point within the mantle. This new magma will rise and punch through the surface of the plate that is riding over top of the descending plate. This causes a whole line of volcanoes. In an oceanic-oceanic collision, you will get a volcanic island arc. Example, Pacific plate subducting beneath North American plate, creating the Aleutian Islands. In an oceanic-continental collision, you will get a volcanic mountain range. Example, the Juan de Fuca plate subducting beneath the North American plate, creating the Cascades Range. As mentioned above, a continental-continental convergence does *not* create a volcanic range. Example, the Himalaya mountains. No volcanism.

   You can also have hot-spot volcanism. This occurs where a magma plume rises to the surface, but the plume itself remains fixed with reference to the Earth geoid. What does this mean? If you were to project a grid on Earth and fix it in space by GPS, then sped up time, the continents and plates could roam all around, but the magma plume would remain fixed. Wherever the plates move over this fixed hot spot, a seamount, then volcano will form (if it is over the hot spot long enough). You can observe the movement of the plate over geologic time by looking at the sequence of volcanic islands or seamounts that get created in a chain. Example, the Hawaiian-Emperor Seamount Range.

   This pretty much sums it up in simple words.

2. 

   Eimear on July 15, 2010 at 5:13 pm

   Earthquakes and volcanoes occur at plate boundaries. Earthquakes occur at a passive (plates slide past each other) and compressional (plates smash together) plate boundaries. Volcanoes form at tensional (plates which pull apart and form shield volcanoes) and compressional plate boundaries (plates compress together to form a composite volcano).

3. 

   Maccerbe on July 15, 2010 at 5:13 pm

   The earth is made up surfaces called ‘Tectonic plates’. When there is sudden and unexpected plate movement this can cause major uproar on earth, wether it consists of earthquakes and freak tsunamis to volcanoes erupting and avalanches. You might want to check out the san francisco earthquake which had a rictor scale of 7 i think it was, this was a major earthquake which destroyed most of the city due to plate movement.

4. 

   aliza on July 15, 2010 at 5:13 pm

   before you get into that you have to know the layers of the earth. the top layers are the most important when discussing plate techtonics. the top most layer is called the lithosphere, and the second layer is the atheosphere. you may have heard other layers of the earth because the earth is layered by many different characteristics, this is the physical characteristics, not the chemical.
   the plates are found within the lithosphere, and are made of oceanic and continental crust. these plates glide over the atheosphere, this is possible because the atheosphere is made of a think warm substance much like the consistency of toothpaste, so there isnt any friction. these plates can move towards eachother(convergent) destroying earth, away from eachother(divergent) creating crust, or against each other(transform). each of these plate boundarys involve geological action. in convergent boundaries, the plates move away from eachother, allowing the molten rock(in the athenoshphere) to rise up, and cool. this causes volcanoes. divergent boundaries are when 2 plates colide and rises, creating mountians. each plate boundary involves some sort of geological acticity, from earth quakes to volcanoes.
   Hope this helped:D