The student knows that plate tectonics is the global mechanism for major geologic processes and that heat transfer, governed by the principles of thermodynamics,

The student knows that plate tectonics is the global mechanism for major geologic processes and that heat transfer, governed by the principles of thermodynamics, is the driving force. The student is expected to:

• C) Explain how plate tectonics accounts for geologic processes and features, including sea-floor spreading, ocean ridges and rift valleys, subduction zones, earthquakes, volcanoes, mountain ranges, hot spots, and hydrothermal vents;

• E) distinguish the location, type, and relative motion of convergent, divergent, and transform plate boundaries using evidence from the distribution of earthquakes and volcanoes

How Plate Tectonics Accounts For:

Sea-Floor Spreading is the process in which the ocean floor is extended when two plates move apart.  As the plates move apart, the rocks break and form a crack between the plates. 

•Earthquakes occur along the plate boundary.  •Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.

How Plate Tectonics Accounts For:

As magma meets the water, it cools and solidifies, adding to the edges of the plates. 

•As magma piles up along the crack, a long chain of mountains forms gradually on the ocean floor.  This chain is called an oceanic ridge.  •When these boundaries form on the continents, they are called Rift Valleys.

The boundaries where the plates move apart are 'constructive' because new crust is being formed and added to the ocean floor. An example of an oceanic ridge is the Mid-Atlantic Ridge.  It is one part of a system of mid-oceanic ridges that stretches for 50,000 miles through the world's oceans. 

How Plate Tectonics Accounts For:

As we’ve already learned, the Earth's tectonic plates can move apart, collide, or slide past each other. The Mid-Ocean Ridge system - the Earth's underwater mountain range - arises where the plates are moving apart. As the plates part, the seafloor cracks. Cold seawater seeps down into these cracks, becomes super-heated by magma, and then bursts back out into the ocean, forming hydrothermal vents.

These hydrothermal vent communities have evolved some of the most interesting communities of organisms on Earth…perhaps showing us the place where life on Earth originated.

How Plate Tectonics Accounts For:

When two oceanic plates collide, the younger of the two plates, because it is less dense, will ride over the edge of the older plate. Oceanic plates grow more dense as they cool and move further away from the Mid-Ocean Ridge

The Marianas Trench, where the enormous Pacific Plate is descending under the leading edge of the Eurasian Plate, is the deepest sea floor in the world.

The Challenger Deep at the trench’s southern end measures nearly 7 miles deep. If Mount Everest was set down in the Pacific at this place, there would still be well over a mile of water left above it.

The older, heavier plate plunges steeply through the athenosphere, and descends into the Earth, where it forms a trench that can be as much as 70 miles wide, more than a thousand miles long, and several miles deep.

Only three descents into the trench have ever been achieved. The first was the manned descent by Trieste in 1960. This was followed by the unmanned ROVs Kaiko in 1996 and Nereus in 2009. Convergent boundaries are referred to as “destructive”.

How Plate Tectonics Accounts For:

One need only look at a map of tectonic plates, and one of earthquake activity, to see the close association.

If we were to remove the clutter of the minimal earthquakes, and only show those equalling 7 or higher on the Richter scale, you can see that all major earthquakes have been centered along tectonic boundaries.

An earthquake, also known as a quake, tremor or temblor, is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquake intensity is measured most commonly in terms of the “Richter Scale”, where each increase in whole number, yields a10-fold increase in intensity. So, a magnitude 7 earthquake is 10 times stronger than a 6, and 100 times stronger than a 5…etc.

Japan 2011Haiti 2010

China 2008

How Plate Tectonics Accounts For:

A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from below the surface

Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together.

Iceland Volcanoes

By contrast, volcanoes are usually not created along transform boundaries, but they may form where there is stretching and thinning of the Earth's crust in the interiors of plates, such as in the East African Rift, and the Rio Grande Rift in North America.

This type of volcanism falls under the umbrella of "Plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are hypothesized to arise from upwelling of magma from the core-mantle boundary, 3,000 km deep in the Earth.

Three Sisters, East of Albuquerque NM, the newest addition to the Rio Grande Rift Volcanic chain.

How Plate Tectonics Accounts For:

Although Hawaii is perhaps the best known hotspot, others are thought to exist beneath the oceans and continents. More than a hundred hotspots beneath the Earth's crust have been active during the past 10 million years. Most of these are located under plate interiors, but some occur near diverging plate boundaries. Some are concentrated near the mid-oceanic ridge system, such as beneath Iceland, the Azores, and the Galapagos Islands.

A few hotspots are thought to exist below the North American Plate. Perhaps the best known is the hotspot presumed to exist under the continental crust in the region of Yellowstone National Park in northwestern Wyoming. There are several calderas (large craters formed by the ground collapse accompanying explosive volcanism) that were produced by three gigantic eruptions during the past two million years, the most recent of which was 600,000 years ago.

As you can see from prior ash layers, the area affected by a volcanic eruption would be immense.

How Plate Tectonics Accounts For:

When two continents carried on converging plates ram into each other, they crumple and fold under the enormous pressure, creating great mountain ranges.

The highest mountain range in the world, the snow-capped Himalayas, is an example of a continent-to-continent collision. This immense mountain range began to form when two large landmasses, India and Eurasia, driven by tectonic plate movement, collided. Because both landmasses have about the same rock density, one plate could not be subducted under the other.

The pressure of the colliding plates could only be relieved by thrusting skyward.

The existence of linear mountain chains on the Earth makes the Earth unique in the solar system.

Although there is volcanism on Venus and Mars and on some of the larger moons, there is no evidence of linear mountain chains.

Linear mountains suggest the movement of a plate boundary and the existence of active plate tectonics

We’ve already shown evidence of convergent and divergent boundaries by looking at the earthquake/volcanic activity maps. What about transform boundaries?

Since transform boundaries are “sliding” past one another, they are obviously a place of great earth movement, and areas of high earthquake activity.Map of midoceanic ridges (red) and deep-sea trenches (blue).

Transform faults are shown in black, cutting the ridges.

Many earthquakes occur along transform plate boundaries.

Three types of transform faults:

• Ridge-ridge

• Ridge-trench

• Trench-trench

are by far the most abundant. The active displacement on these faults occurs only between the ridge segments, as shownabove. No movement occurs along the rest of the fracture zone.

are much less common. They form an important connection between diverging and converging plates. The longest transform faults are all of this kind.

are also rare. These faults appear to connect trenches together.

Transform faults can connect convergent and divergent plate boundaries in various combinations. In all cases, the trend (or movement) of a transform fault is parallel to the direction of relative motion between plates.