Mountains, basins and unique topography can form along transform boundaries depending on the fault’s geometry, the rock type and how parallel the motion of the plates are to the strike of the fault.
Earthquakes associated with transform boundaries are relatively shallow occurring at depths of ~0-20 km beneath the surface. Like all plate boundaries, the movement of crust along transform and strike-slip faults creates earthquakes. Transform boundaries also form on larger scales on land like the San Andreas fault in Western North America and the Alpine fault in New Zealand. As shown in the map below, they are particularly common along divergent plate boundaries where they connect sections of oceanic spreading centers or mid-ocean ridges, helping create some of the longest topographic features on the planet. Transform boundaries occur all over the world and come in many shapes and sizes. Similarly, if the same situation occurred and the fault was left-lateral, the tree would move left. As shown below, a person standing on one side of a right-lateral strike-slip fault will watch a tree on the opposite side move right as the fault slips. Transform boundaries can be dextral (right-lateral) or sinistral (left-lateral) with fault planes near vertical or dipping steeply in one direction. Instead, due to the relative motion of the plates being parallel to and in opposite directions across the fault, the plates slide past each other laterally. Unlike divergent (constructive) and convergent (destructive) plate boundaries, lithosphere at transform boundaries is neither created nor destroyed deeming them “conservative” plate boundaries. The Caribbean volcanic islands form a curved linear chain or ‘volcanic island arc’ parallel and to the west of the Puerto Rico Trench.Transform boundaries occur where the Earth’s tectonic plates slide past each other horizontally along transform or strike-slip faults. The eruptions on Montserrat during the 1990s are a good example of this type of activity. These volcanoes typically produce ash and pyroclastic flows, as well as small amounts of andesitic lava. The water and gases in andesitic magma account for the explosive activity of andesitic volcanoes, which typically lie dormant for many hundreds or thousands of years. It is viscous, trapping gases as it rises. This produces magma, which rises and may be erupted explosively as andesite at the surface.Īndesitic magma is less dense than the surrounding material, and can have a temperature of 1000 oC. As the plate heats up the water is liberated, lowering the melting point of the mantle and causing partial melting. This results in frequent shallow focus earthquakes that get deeper as the ocean plate descends further, defining a zone of earthquake foci known as a Benioff zone.Ĭontinued subduction of the South American Plate brings sea water, locked in the ocean crust, deep into the mantle. As the South American Plate descends, it drags against the overlying plate, causing both to fracture and deform.
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