Where is Volcanic Rock Found?

Volcanic rock is formed from magma, molten material beneath the Earth’s surface that erupts through cracks or fissures onto the surface as lava or volcanic ash. The minerals and glass in the lava or ash crystallize and solidify into volcanic rock. So volcanic rock is found wherever volcanoes currently exist or existed in the past. Here are the main regions where volcanic rock can be found:

Active Volcanic Zones

Places with active volcanoes obviously have volcanic rock. There are roughly 1,500 active volcanoes around the world, concentrated along the edges of tectonic plates where subduction is occurring. Major active volcanic zones include the “Ring of Fire” around the Pacific Ocean (the west coasts of North and South America, Kamchatka in Russia, Japan, the Philippines, Indonesia, and New Zealand). Other active zones include Italy, Iceland, Africa’s Great Rift Valley, Hawaii, and underwater volcanic ridges like the Mid-Atlantic Ridge. Volcanic rocks in these areas are freshly formed.

Dormant Volcanic Regions

Dormant volcanoes are those that have erupted in recorded history but are currently inactive. Dormant volcanic areas may still erupt again in the future, so the volcanic rocks there are not brand new but are generally on the scale of hundreds to thousands of years old. Regions with dormant volcanoes include the Andes Mountains, Central America, the Southwestern United States, the islands of the South Pacific, Scotland, Germany, Turkey, and Armenia.

Extinct Volcanic Areas

Extinct volcanic regions are places where volcanoes last erupted over 10,000 years ago. Without current seismic and volcanic activity, these areas are unlikely to erupt again. But the old volcanic rocks remain as evidence of ancient lava flows and ash falls. Extinct volcano sites include the Canadian Shield, Siberia, Scotland, Norway, Greenland, India’s Deccan Traps, Australia’s Nullarbor Plain, and many other locations where plate tectonics have shifted. The volcanic rocks in these areas can range from 10,000 years to over 2 billion years old.

Subduction Zones

Places where oceanic tectonic plates are being subducted under continental plates accumulate volcanic rock over millions of years. Powerful friction and pressure melts the upper mantle into magma, which rises in plumes through the continental crust. Subduction zones typically have large batholith formations, made up of granite that cooled underground, as well as extrusive igneous rocks on the surface. The Pacific Northwest and Andes have extensive volcanic rock deposits from subduction.

Rift Valleys

Rift valleys form when tectonic plates slowly spread apart. As the plates diverge, magma wells up from the mantle to fill the gap. Lava spills out along these constructive boundaries between plates. The East African Rift Valley is an example of a place with ongoing rifting and associated vulcanism. Other famous rift valleys like the Rhine River Valley also feature thick layers of basaltic lava although they are no longer active spreading zones.

So in summary, volcanic rock can be found anywhere with currently or previously active volcanoes, subduction zones, or rift valleys. The type of volcanic rock depends on the specific eruption and cooling history at each site. But overall, volcanic rocks are widespread, covering about 8% of the Earth’s current land surface.