This web site is intended to give a brief look at some of the volcanoes in Arizona. All of these volcanoes are inactive and have been that way for a long time. A volcano is a hill or mountain that forms from the accumulation of matter that erupts at the surface. There are several different types of volcanoes. These volcanoes are produced by a variety of magma types.
Basaltic lava is one type of magma.
It has a low viscosity and silica content. There are several categories of this type. Flood basalts that are highly fluid and erupt on flat terrain. Pahoehoe forms when highly fluid lava spreads in thin sheets and a thin glassy elastic skin congeals on its surface as it cools. These two types of lava are formed on a slope.