At a constructive plate boundary, two tectonic plates are moving away from each other, creating a new pathway for rising hot magma from the mantle to reach the surface. As the plates move apart, magma rises from the mantle to the Earths surface, forming shield volcanoes with wide and gently sloping sides. These eruptions are typically prolonged and less explosive than those at destructive plate boundaries. The process of fracturing, injection, and eruption is repeated frequently, so that tensional stresses do not have time to accumulate significantly, and as a result, constructive plate boundaries are characterized by frequent, low-magnitude seismicity occurring at shallow crustal depths along the ocean ridge systems.