Spreading centers are places where tectonic plates are diverging (moving away from one another). As the plates separate, a pathway is created for magma to move toward the surface. Spreading centers can extend into continental plates, such as The Great Rift Valley in East Africa. Magma produced at spreading centers is mafic. Therefore, much of the oceanic crust is made of basalt, a mafic rock.
Some of the magma produced at spreading centers erupts as lava flows and pyroclastic material, but most of it cools internally below Earth's crust. Fault zones are areas where the crust is cracking, usually due to the movement of the tectonic plates. Earthquakes and volcanism are common around fault zones.
There are no areas of active sea-floor spreading found within a national park of the United States. The country of Iceland, however, continues to grow due to the phenomenon. There are a few national parks that have evidence of past volcanism in rift valleys.
Isle Royale National Park, Michigan [Geodiversity Atlas
] [Park Home
Keweenaw National Historical Park, Michigan [Geodiversity Atlas] [Park Home
Petroglyph National Monument, New Mexico [Geodiversity Atlas] [Park Home]