Transform faults in continents show strike-slip offsets during earthquakes and are high angle faults with dips greater than 70°. Over millions of years, the Pacific Plate has moved over the hot spot, creating a chain of volcanic islands.Transform boundaries on the continents include the San Andreas fault in California, the North Anatolian fault in Turkey, the Alpine fault in New Zealand, and, by some definitions, the Altyn Tagh and Red River faults in Asia. The Hawai’ian hot spot causes magma to rise and erupt as lava on the ocean floor. The Hawai’ian Islands are a chain of volcanoes in the middle of the Pacific Plate, which have formed due to the presence of a hot spot. Heat from the mantle plume causes melting and thinning of the crust, which leads to volcanic activity at the surface. It is also referred to as hot spot or intraplate volcanism. This may happen in areas that are distant from plate boundaries. Volcanoes can also form above a column of superheated magma called a mantle plume. Here, the pushing together of two continental plates results in the mountain forming processes that shaped, for example, the Alps and Himalayas. Note: There is a third setting of destructive boundary: continent-continent. It is this process that allows the generation of magma at depth that feeds volcanoes that are formed at the surface. Water has the effect of reducing the melting temperature of the mantle by about 60–100☌. As the subducted oceanic plate sinks and heats up, water is gradually released from the sediments and minerals within the plate ‘slab’. Subduction provides a mechanism for introducing water-bearing sediments into the mantle. This illustration shows ocean-continent subduction. Volcanoes can form at subduction zones where tectonic plates are moving towards each other and one plate descends beneath the other. The majority of volcanism in Iceland occurs along volcanic rift zones that cut through the centre of the island. Some are extinct, but over 30 are still active. The island is covered with more than 100 volcanoes. As the plates pull apart, molten rock (magma) rises up and erupts as lava, creating new ocean crust. Iceland lies on the Mid Atlantic Ridge, a constructive plate boundary, where the North American and Eurasian plates are moving away from each other. Volcanoes can sometimes form in these setting one example is Iceland. The Earth’s crust is pulled apart to create a new pathway for rising hot magma to flow on to the surface. Read more Constructive plate boundary volcanoesĪt constructive plate boundaries, the tectonic plates are moving away from one another. It erupts from vents, sometimes as lava, but usually the magma becomes solid within the volcanic vent, giving much more explosive eruptions.Īuthor Chris King, reproduced with the author’s permission from Exploring Geoscience Across The Globe. The eruption of intermediate and silicon-rich magma is very different. Rivers of lava can flow over the ground or move more slowly as blocky masses bulldozing along. When runny basaltic magma erupts as lava, it pours out of the ground along long surface cracks or through volcanic vents and may be sprayed into the air as spectacular lava fountains. So in summary, iron/magnesium-rich basaltic magmas are free-flowing with low viscosity, while intermediate and silicon-rich magmas are very sticky with high viscosity.

When magmas contain a lot of gas this makes them more runny too, although basaltic magmas usually do not contain much gas.

Basaltic magmas also tend to contain few crystals, increasing their runniness. Basaltic magmas are also usually the hottest and the hotter the magma is the less viscous it is as well. The balance between iron/magnesium and silicon composition changes the runniness: iron/magnesium-rich basaltic magmas are the most runny (low viscosity) at one end of the scale and silicon-rich are the least runny (highly viscous) at the other end. What are we doing about climate change?.Understanding carbon capture and storage.What causes the Earth’s climate to change?.NGR hydrocarbons (well samples) database.Palaeontology and biostratigraphy collections.Donations and loans of materials collections.

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Transform boundary