PTR - Effects of Plate Tectonics Lesson

 

Effects of Plate Tectonics

Mountains

As mentioned previously, a variety of geological landforms and hazards can result due to the movement of these enormous sections of the Earth's crust. The continents have been moving for billions of years and have been colliding and breaking apart time after time. Viewed at high speed, these collisions would have looked like a demolition derby. Collisions between continents produce mountain ranges and, just like on a car that was involved in an accident, these scars from previous collisions remain long after the impact is over. The Appalachians in North America, and the Pyrenees and Alps in Europe, are remainders of previous plate collisions.

Volcanoes

When collisions involve continental crust and oceanic crust, the subduction of the oceanic crust results in the production of large amounts of magma that work their way towards the surface. The effects of these magma chambers can result in volcanic (or potentially volcanic) mountain ranges ("Ring of Fire", Rocky Mountains in North America, Andes in South America).

Several factors determine the type of volcano that can form at these boundaries.

Thin, free-flowing magma rises to the surface and spreads out over large areas, forming relatively flat volcanoes known as shield volcanoes. The volcanoes in Hawaii and Iceland are examples of typical shield volcanoes:

Cinder cone volcanoes are more explosive, ejecting small chunks of lava into the air that harden into small rocks and ash that pile up to form the cone:

Other volcanoes form both types of materials, and are known as composite volcanoes. Because the runny lava helps hold the cone together, these volcanoes can grow to be much taller than the other types:

Some volcanoes arise not due to a close proximity to a plate boundary, but because of an unusually hot part of the mantle. The intense heat causes the crust above to melt away, forming magma chambers and volcanoes, but tectonic plate movement eventually slides these volcanoes off of the "hot spot", which not only causes the current volcano to go dormant, but also leads to the formation of new volcanoes behind it. Over time, a chain of extinct, dormant, and active volcanoes is the result of tectonic plate movement over a "hot spot".

Over time, the conditions that once caused a volcano to erupt may change, and the volcano may go dormant or become completely extinct. In some cases, a volcano may eventually collapse into the open space that once contained magma underground. This collapse leaves a large crater, called a caldera, where the volcano once was. Ngorongoro crater, in Tanzania, is a caldera that formed when the volcano collapsed around 3 million years ago. Over 10 miles across, it is the largest unbroken, un-flooded caldera on Earth.

Faults

Transform boundaries are known primarily for creating earthquakes as the plates grind past each other, but they are not the only regions that cause tremors. Faults are fractures in the rocks of the crust and allow movement of one side relative to the other side. The rock on each side of a fault can be described as a "hanging wall" or a "footwall"; the hanging wall protrudes farther at the top of the rock, where the footwall protrudes farther at the bottom:

In the case of divergence - where the rock on each side of the fault are being pulled apart - the fault is called a normal fault and results in one side dropping relative to the other side.

When the rocks on each side of the crack are forced towards each other, one side slides up and over the other side, resulting in a reverse fault.

Faults in which one side slides along the other side are known as strike-slip faults and are characteristic of transform boundaries.

 

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