Divergent Boundaries

Imagine that you are a geographer studying what is below the earth's surface; picture two giant conveyor belts, facing each other but slowly moving in opposite directions. Click on the link below to see divergent boundaries at work.

This activity might not be viewable on your mobile device.Divergent Boundaries

This is an example of divergent boundaries which occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle.

Interactive exercise. Assistance may be required. Click the Divergent Boundaries button to see why they are important for us to study.

Tips for Mobile Device Users

Image of a map of Iceland and an illustration of the Mid-Atlantic Ridge that runs through it. There are arrows depicting the left half of the map as the North American Plate and the right half of the map as the Eurasian Plate. The arrows indicate movement in opposite directions.

Source: Map of Mid-Atlantic Range splitting Iceland and separating North American Plate and Eurasian Plate, U.S. Geological Survey

The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates.

Activity

Answer the following question in your notes:

The Mid-Atlantic Ridge moves about 2.5 centimeters per year- this equals 25 kilometers in 1million years! If you were a geographer (or another type of scientist) studying this information:

Convergent Boundaries

This type of tectonic force occurs where crust is destroyed as one plate dives under another. Depending upon where this plate collision takes place, convergence boundaries form what we know as mountain ranges, volcanic activity, and even earthquakes.

This is an image of hot lava splashing against volcanic rock.

Source: Lava fountains spouting from eruptive fissures during the October 1980 eruption of Krafla Volcano, Gudmundur E. Sigvaldason, U.S. Geological Survey

Video segment. Assistance may be required. Take a look at this news report about a volcano that erupted in Iceland in April of 2010.

Source: Iceland volcano eruption continues, more test flights through ash planned, Russia Today, YouTube

In your notes, complete the following:

To learn more about volcanoes,click here.

Interactive popup. Assistance may be required.

The "Ring of Fire" is an arc stretching from New Zealand, along the eastern edge of Asia, north across the Aleutian Islands of Alaska, and south along the coast of North and South America. The Ring of Fire is composed of over 75% of the world's active and dormant volcanoes.

Image of the map of the Ring of Fire.
This huge ring of volcanic and seismic (earthquake) activity was noticed and described before the invention of the theory of plate tectonics. We now know that the Ring of Fire is located at the borders of the Pacific Plate and other major tectonic plates.Close Pop Up

Convergence: Subduction

Image of the oceanic-continental convergence model that is the conveyor belt meeting and the oceanic crust on the left side is sinking . On the surface, there is a volcanic arc above the continental crust on the right side of the image. There is a depiction of volcanic eruption in this area.

Earth's size has not changed much during the past 600 million years. Scientists believe this is due to the crust being destroyed at the same rate that it is being created (remember the conveyor belt).

Such destruction (recycling) of crust takes place along convergent boundaries where plates are moving toward each other, and sometimes one plate sinks (subduction) under another. The location where the sinking of a plate occurs is called a subduction zone. As the bottom plate starts to melt, magma rises and forms volcanoes at the surface.

Image of the snow-capped Andes Mountains.

Source: The Convergence of the Nazca and South American Plates, George Erickson, U.S. Geological Survey

Convergent Boundaries

Off the coast of South America along the Peru-Chile trench, the oceanic Nazca Plate is pushing into and being subducted under the continental part of the South American Plate. In turn, the overriding South American Plate is being lifted up, creating the towering Andes Mountains (as pictured here), and surrounding ridges, the backbone of the continent. Strong, destructive earthquakes and the rapid uplift of mountain ranges and ridges are common in this region.

Convergent Collision

When two continental plates collide, neither one is subducted; also the plates buckle and fold. Sometimes a double thickness of crust results in the formation of mountain ridges. The image to the right is a continental-continental convergence. Look at the example of the continental-continental convergence model here.

Image of the continental-continental convergence. In this model, the continental slightly sinks below the continental crust as the two collide. Above the surface, a mountain range is formed.

Source: Continental-Continental Convergence, U.S. Geographical Survey

A Real World Example

This photo is a sunset view of towering, snow-capped Mt. Everest, a famous peak in the Himalayan Mountain Range in Nepal. The Himalayas, the highest mountains on earth, are an example of convergence collision. The Himalayas rise 1cm per year- that is growth rate of 10km in a million years. Look at the photo below to get an idea of how tectonic forces work over time.

Image of Mt. Everest that is snow-covered, but looks like lava because of the sunset.

Source: Mt. Everest, from the village of Lobuche (Solu-khumbu), Nepal, Gimmy Park Li, U.S. Geological Survey

Image of the bottom of a mountain that is lined with trees at the bottom and a rock formation exists as it elevates and there are trees at the top.

Source: India. Giant talus in the Himalaya foothills near Dehra dun, Sahasradhara, 1964, McKee, U.S. Geological Survey

Image of a map of The Himalaya Mountains, making up the Tibetan Plateau to the north. India is located South of the range.

Source: The Himalayan Mountains, NASA

This is a satellite map of Asia, provided by NASA, where the Himalayas are clearly shown.