The majority of volcanism in Iceland occurs along volcanic rift zones that cut through the centre of the island. At constructive plate boundaries, also known as divergent boundaries, tectonic plates move away from one another to produce volcanoes.
Hot magma rises from the mantle at mid-ocean ridges, pushing the plates apart. The interaction of these two types of volcanism, over the last 15 million years or more, has created the island of Iceland. Destructive, or convergent, plate boundaries are where the tectonic plates are moving towards each other. Volcanoes form here in two settings where either oceanic plate descends below another oceanic plate or an oceanic plate descends below a continental plate.
This process is called subduction and creates distinctive types of volcanoes depending on the setting:. Volcanoes can form at subduction zones where tectonic plates are moving towards each other and one plate descends beneath the other. This illustration shows ocean-continent subduction. Subduction provides a mechanism for introducing water-bearing sediments into the mantle.
It is this process that allows the generation of magma at depth that feeds volcanoes that are formed at the surface. Note: There is a third setting of destructive boundary: continent-continent. Here, the pushing together of two continental plates results in the mountain forming processes that shaped, for example, the Alps and Himalayas.
Volcanoes can also form above a column of superheated magma called a mantle plume. This may happen in areas that are distant from plate boundaries.
It is also referred to as hot spot or intraplate volcanism. Heat from the mantle plume causes melting and thinning of the crust, which leads to volcanic activity at the surface. Over millions of years, the Pacific Plate has moved over the hot spot, creating a chain of volcanic islands. This simple schematic diagram shows the movement of the tectonic plate light brown over a mantle plume, or hot spot, to produce a chain of volcanic islands. The superheated magma rises through the mantle yellow , melts the crust above brown and flows on to the surface forming a volcano.
Diagram not to scale. Discovering Geology introduces a range of geoscience topics to school-age students and learners of all ages. The Earth beneath our feet is constantly shifting and moving, and violently with catastrophic and immediate results. Where are volcanoes found? Volcanoes usually form along plate boundaries , where tectonic plates are either moving towards or away from one another: Constructive boundary or divergent boundary - this is where two plates move away from one another.
Magma rises up to fill the gaps between the plates usually to create a shield volcano. Destructive boundary or convergent boundary - this is where two plates move towards one another. Improve this page Learn More. Skip to main content. Module 9: Volcanoes. Search for:. Reading: Volcanoes at Plate Boundaries Volcanoes are fun and difficult to climb. Convergent Plate Boundaries Converging plates can be oceanic, continental, or one of each. Melting Melting at convergent plate boundaries has many causes.
Figure 3. Baker, Washington. Figure 4. A volcanic eruption at Surtsey, a small island near Iceland. Figure 5. Mount Gahinga in the East African Rift valley. Explore More Use this resource to answer the questions that follow. What percent of volcanoes and earthquakes occur on the Pacific Ring of Fire? How long is the arc of volcanoes along the Pacific Rim? How has Augustine built up so high? Does it have high or low silica?
What type of volcanoes are found along the ring of fire? What happens to the gas in the magma? What does water do in hot rock below the surface? What does carbon indicate? What process brings the sediments and water into the mantle?
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