The four types of lava are basaltic, andesitic, dacitic and rhyolitic. Basaltic is further divided into pillow, a'a and pahoehoe lava. The primary difference among these types is the amount of silica they contain. Higher silica content results in slower, cooler and more explosive flows.
Basaltic lava flows are the hottest and the most common, appearing as pillow flows when volcanoes erupt under water or ice. These flows build up, creating submarine mountains and islands over time. Rhyolitic flows are thick and slow, creating crystallizing rocks such as granite. Andesitic lava is common in the Andes Mountains and is an intermediate form between basaltic and rhyolitic. Dacitic is between rhyolitic and andesic in viscosity.