Plate tectonics provides us with a dynamic photo of our planet. Plates continually relocate over the hot, partly molten rocks in the mantle. They converge together, move apart, and also scrape by each other. In the process, tall mountain chains are slowly and steadily uplifted and also worn down, and broad ocean containers are opened and closed as continents come together and also split apart. Nothing on planet is permanent, since heat consistently flows native the warm interior come the cooler surface, and mantle convection provides the major mechanism for that heat transfer. The range of these recurring processes is vast, practically outside our ability to comprehend, yet we are periodically reminded the the strength of geological processes.

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For hundreds of years humans have realized the Earth’s most violent events—volcanoes and earthquakes—do not happen randomly. Earthquakes are common in California and Alaska, yet extremely rarely in Kansas or Florida. Volcanoes are commonplace in Hawaii and also the Pacific Northwest however never appear in brand-new York or Texas. Why have to this be? key tectonics gives an answer.

Plates and also Volcanism

The worldwide distribution of volcanoes may be interpreted in regards to the principles of key tectonics. Volcanoes are typical in 3 geological situations: follow me divergent plate boundaries, near convergent bowl boundaries, or above places referred to as “hot spots.”

1. Divergent key Boundaries

The formation of brand-new crust follow me volcanic dispersing ridges of divergent plate boundaries is the principal method that new crustal rocks are developed (see number 17-14 below). Brand-new basaltic bowl material creates at the rate of a couple of centimeters per year along around 85,000 km of oceanic ridges about the world.

2. Convergent plate Boundaries

Volcanoes are likewise common close to subduction zones, other than where 2 continental tectonic key collide. As water-rich crustal material plunges right into the mantle, it becomes hotter and may partially melt. This magma, i beg your pardon is highly mobile fluid rock, rises to the surface to form chains the volcanoes, typically around 200 kilometres inland indigenous the line of subduction. The “Ring that Fire,” a dramatic cable of volcanoes that borders much of the Pacific Ocean, is a direct repercussion of plate subduction (see number 17-19 below).

The volcanoes that kind the Cascade hill chain follow me the northwestern coast of the United states (including mount Rainier and also Mount St. Helens) space striking examples of the processes linked with subduction of one oceanic plate in ~ a continent. Regular dramatic eruptions of similar volcanoes in main America, Japan, and the Philippines point to other areas where subduction and also volcanism take place in tandem.

3. Warm Spots

Finally, hot spots are a dramatic kind of volcanism indirectly associated with plate tectonics. Earth scientists acknowledge dozens of hot spots approximately the world, consisting of Hawaii, Yellowstone Park, Iceland, and others where huge isolated chimney-like columns the rising warm rock, additionally known together mantle plumes, climb to the surface much more or much less like bubbles coming to the surface ar in water being heated on a stove. This plumes might originate in the reduced mantle or also at the core–mantle boundary. On a geological timescale, sources of warm spots are relatively stationary, so if a tectonic plate progressively moves over the fixed warm spot, the result will be a chain that volcanoes choose the Hawaiian Islands that are constructed through a collection of basaltic lava eruptions (see number 17-20 below). This islands were developed one at a time together the Pacific bowl moved over the localized hot spot. The present-day volcano Kilauea on the “big island” the Hawaii, the website of most of the island chain’s active volcanism, is straight over a hot spot. The volcanic islands to the northwest are progressively older, as well as smaller owing to erosion, revealing the the movement of the Pacific bowl is likewise toward the northwest. In fact, a collection of eroded submarine peaks the were islands countless years earlier stretches numerous kilometers farther come the northwest. In numerous million years, the many northwesterly that the existing Hawaiian archipelago will have been eroded in ~ the waves, but brand-new volcanic task has already begun on the s floor south east of Kilauea, promising a new island the has already been given the surname “Loihi” by islanders.

FIGURE 17-14. diagram of a common divergent plate boundary in an s setting.

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FIGURE 17-19. Diagram of a usual convergent plate border in an s setting.

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FIGURE 17-20.

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diagram of Pacific plate movement with respect to the Hawai’I warm spot.