Three types of Plate Boundaries

Three types of Plate Boundaries

Author: Aimee Carter

Lesson Objective:

Students will be able to identify and label the distinctive features of the three types of plate boundaries and explain the affects they have on the formation of the earth’s surface.

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In order to meet the stated objective, please complete the following tasks the order is not as important as reviewing the reading and viewing the content:

1) Review-Notes from Dynamic Earth Module

2)  View "Geology Kitchen #9 - Plate Tectonics" - YouTube Video

3) View "Cracked Up" - YouTube Video

4) Take the quiz 

5) Lastly, Draw a model and label each of the three plate boundaries. Include a brief description of each plate boundary.

Don't forget to add the accurate land formations associated with the plate boundary.

Notes from Dynamic Earth Module

Convergent Boundaries — Colliding Plates

At convergent boundaries, tectonic plates collide with each other. The events that occur at these boundaries are linked to the types of plates — oceanic or continental — that are interacting.

Subduction Zones and Volcanoes

At some convergent boundaries, an oceanic plate collides with a continental plate. Oceanic crust tends to be denser and thinner than continental crust, so the denser oceanic crust gets bent and pulled under, or subducted, beneath the lighter and thicker continental crust. This forms what is called a subduction zone. As the oceanic crust sinks, a deep oceanic trench, or valley, is formed at the edge of the continent. The crust continues to be forced deeper into the earth, where high heat and pressure cause trapped water and other gasses to be released from it. This, in turn, makes the base of the crust melt, forming magma.

The magma formed at a subduction zone rises up toward the earth's surface and builds up in magma chambers, where it feeds and creates volcanoes on the overriding plate. When this magma finds its way to the surface through a vent in the crust, the volcano erupts, expelling lava and ash. An example of this is the band of active volcanoes that encircle the Pacific Ocean, often referred to as the Ring of Fire.

A subduction zone is also generated when two oceanic plates collide — the older plate is forced under the younger one — and it leads to the formation of chains of volcanic islands known as island arcs. Examples include the Mariana Islands in the western Pacific Ocean and the Aleutian Islands, off the coast of Alaska.

Since the collision and subduction of plates is not a smooth process, large, powerful earthquakes are another phenomenon that result from this type of interaction. Earthquakes generated in a subduction zone can also give rise to tsunamis. A tsunami is a huge ocean wave caused by a sudden shift on the ocean floor, such as an undersea earthquake. If the wave reaches land, it can cause incredible destruction, like the Asian Tsunami, which killed more than 200,000 people in 11 countries across the Indian Ocean region in December 2004.

Collision Zones and Mountains

What happens when two continental plates collide? Because the rock making up continental plates is generally lighter and less dense than oceanic rock, it is too light to get pulled under the earth and turned into magma. Instead, a collision between two continental plates crunches and folds the rock at the boundary, lifting it up and leading to the formation of mountains and mountain ranges.

An example of this mountain-building process is the Himalayan range in southern Asia. Containing the highest mountain peaks in the world and traversing the modern-day countries of India, Pakistan, China (Tibet), Bhutan, and Nepal, the Himalayas were formed by the collision of the Indian and Eurasian Plates. This process began after the breakup of Pangaea, when India became an island continent and began traveling northward toward Asia. The island of India slammed into Asia about 40 to 50 million years ago near modern-day Tibet, crushing and folding the plates to form the Himalayan mountain range. Its best known peaks, Mount Everest and K2, are among several that measure over 8,000 meters (26,000 feet) high at their summits. Since the Indian Plate is continuing in its northward movement into Asia, the Himalayas continue to grow higher each year by small amounts (5 to 20 mm or 1 inch per year).

Divergent Boundaries — Spreading Plates

At divergent boundaries, tectonic plates are moving away from each other. But if these huge masses of crust are moving apart, what happens in the space left between them?

Seafloor Spreading

Divergent boundaries in the middle of the ocean contribute to seafloor spreading. As plates made of oceanic crust pull apart, a crack in the ocean floor appears. Magma then oozes up from the mantle to fill in the space between the plates, forming a raised ridge called a mid-ocean ridge. The magma also spreads outward, forming new ocean floor and new oceanic crust.


When two continental plates diverge, a valley like rift develops. This rift is a dropped zone where the plates are pulling apart. As the crust widens and thins, valleys form in and around the area, as do volcanoes, which may become increasingly active. Early in the rift formation, streams and rivers flow into the low valleys and long, narrow lakes can be created. Eventually, the widening crust along the boundary may become thin enough that a piece of the continent breaks off, forming a new tectonic plate. At this point, water from the ocean will rush in, forming a new sea or ocean basin in the rift zone.

Transform Boundaries — Grinding Plates

At transform boundaries, tectonic plates are not moving directly toward or directly away from each other. Instead, two tectonic plates grind past each other in a horizontal direction. This kind of boundary results in a fault — a crack or fracture in the earth's crust that is associated with this movement.

Faults and Earthquakes

Transform boundaries and the resulting faults produce many earthquakes because edges of tectonic plates are jagged rather than smooth. As the plates grind past each other, the jagged edges strike each other, catch, and stick, "locking" the plates in place for a time. Because the plates are locked together without moving, a lot of stress builds up at the fault line. This stress is released in quick bursts when the plates suddenly slip into new positions. The sudden movement is what we feel as the shaking and trembling of an earthquake.

The motion of the plates at a transform boundary has given this type of fault another name — a strike-slip fault. The best-studied strike-slip fault is the San Andreas Fault in California. It is located at the boundary between the Pacific and North American plates and runs roughly 800 miles (1,300 km) through Northern and Southern California. As the two plates grind past each other — the Pacific Plate moving northwest and the North American Plate moving southeast — the motion produces numerous earthquakes along the fault. While many are small and cause only minor trembling, the San Andreas Fault has also been the site of major events: the 1857 Fort Tejon earthquake, the 1906 San Francisco earthquake and fire, and the 1989 Loma Prieta earthquake. Many scientists believe that the San Andreas Fault is due to unleash another large earthquake — a "big one" — in the coming decades.

Source: Quinn, A. (2007). Dynamic Earth. Retrieved March 12, 2016, from http://www.learner.org/interactives/dynamicearth/slip2.html

Geology Kitchen #9 - Plate Tectonics