At the surface of plate A, several geologic features may form depending on the tectonic setting, especially if plate A is involved in a convergent boundary where another plate (plate B) is subducting beneath it:
- Volcanoes : As plate B subducts and descends into the mantle, it melts due to increasing temperature and pressure, generating magma. This magma rises through plate A and erupts at the surface, forming volcanoes. These can be volcanic island arcs if both plates are oceanic or volcanic arcs on continental crust if plate A is continental
- Earthquakes : The interaction and grinding between plate A and the subducting plate B generate tectonic earthquakes along the boundary
- Deep Ocean Trenches : At the subduction zone where plate B sinks beneath plate A, a deep trench or submarine valley forms on the ocean floor adjacent to plate A
- Tsunamis : Sudden movements or uplift of plate A’s edge during subduction can displace large volumes of water, potentially causing tsunamis
If plate A is at a different type of boundary, other features might form:
- At a divergent boundary , new crust forms as magma rises, creating mid-ocean ridges or submarine mountain ranges
- At a transform boundary , fault lines and earthquakes occur due to plates sliding past each other horizontally
In summary, at the surface of plate A in a convergent setting with subduction, expect volcanoes, earthquakes, trenches, and potentially tsunamis as key geologic features