Analytics

Both plates are moving in a northwesterly direction, but the Pacific Plate is moving faster than the Philippine Plate. The movement of these plates creates a convergent plate boundary as the increased speed of the Pacific Plate causes it to collide with the Philippine Plate. This collision creates a subduction zone in the Mariana Trench as the Pacific Plate sinks into the mantle and below the Philippine Plate. This collision occurs at different speeds along the curved plate boundary, but the average relative motion is on the order of tens of millimeters per year. Recurrent earthquakes occur along this plate boundary because the descent of the Pacific plates into the mantle is neither smooth nor uniform. Instead, the plates usually get stuck as pressure builds up, but with sudden slips as the plates move from a few millimeters to a few meters at a time. When plates slide, vibrations occur, and these vibrations propagate through the earth’s crust as seismic waves. As the Pacific Plate descends into the mantle, it heats up from friction and the geothermal gradient. At a depth of about 100 miles, the rocks have heated to a point where some minerals are beginning to melt. This fusion creates magma, which due to its lower density, rises to the surface. When magma reaches the surface, volcanic eruptions occur. These eruptions formed the Mariana Islands archipelago.