Separating plates At divergent margins, tectonic plates are coming apart and hot rock forces its way to the surface between them. Many divergent plate margins are under the oceans, creating long undersea rift zones that fill with lava. Lava Types Magma comes in different ''flavors'' or compositions. Each of these will produce a different lava ranging from fluid, fast moving basalt to slower, more viscous andosite. Because rocks are made up of collections of minerals that melt at different temperatures, the make up of the rock being melted affects the magma that results.
Scientists can often find clues about past eruptions by studying the deposits left behind.
Areas affected by lava flows, debris flows, tephra or pyroclastic flows can be mapped, making disaster planning more effective. In addition to this type of long range forecasting, scientists are becoming more and more skilled at spotting the warning signs of an eruption. Causes of death by volcanoes erupting in the last 400 years look at this link. The Different Kinds of Volcanoes. Many people think that there is only one type of volcanic eruption because they are all so bad, but there are a couple.