The mantle rock is now in a zone of lower pressure as it is closer to the surface of the planet. This caused the mantle to swell outward to replace the zone that once was occupied by the formerly thick crust. Geologists say that "magma follows tectonics." As the crust was stretched, this created a zone of relatively low pressure in the lithosphere. As the region west of the Colorado Plateau thinned and fractured crust, magma can rise through these fractures and erupt on the surface. There are two main reasons why there is so much volcanism in the area. The volcanic fields in this region are actively monitored and only the one near Flagstaff has shown any unrest. Helens-style eruption, it will be like what was seen in at Kilauea in Hawaii in 2018. ![]() If we do, it will not likely be a catastrophic Mt. It is worth mentioning that it is highly unlikely we will see an eruption in the next century. This page explains how magma is injected in the crust, why there is such a range in eruption types from lava fountains and lava flows to explosive pyroclastic events. The first section on the Colorado Plateau and the Basin and Range, as well as the Geology section of the website, provided a solid foundation to understand Basin and Range crustal extension. Uinkaret VF magma comes from about 15 to 55 miles below the surface. ![]() This diagram shows that rising magma follows zones of weakness, either horizontal, forming a sill, or vertical, forming a dike.
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