Parashant is a wonderland of deeply cut canyons, plateaus, basins...and volcanoes! The Grand Canyon-Parashant landscape is dual story of Basin and Range stretching and Colorado Plateau uplift. On the west side of the monument Earth's crust has cracked and slumped to the west over the last 17 million years, thinning the crust significantly. This crustal extension doubled the surface distance from Parashant west to the Pacific Ocean. This thinning in turn caused Earth's mantle to swell upward to replace the stretched crust due to isostacy. Not only did this swelling put hot mantle rock closer to the surface, it pushed the Colorado Plateau thousands of feet higher in elevation than it otherwise would be over the last six million years. This set the stage for both erosion, including the cutting of the Grand Canyon, and the hundreds of volcanic eruptions mapped in the monument. At least 213 eruptions have occurred in Parashant's Uinkaret Volcanic Field. The most recent happened only about 950 years ago. Several nearby volcanic fields have also erupted in the last few thousand years. There will be more in the near future. This story is not unique to Parashant. In fact volcanism, Basin and Range stretching, and uplift of the Colorado Plateau is a story that spans four states from southern Utah to northern Arizona to northern New Mexico and western Colorado.
A new development in geologic circles that seems to explain why there has been so much volcanism in the region is a phenomenon that is still poorly understood but being actively researched. Ground scans to the lower crust and upper mantle appear to show that the base of the Colorado Plateau is melting and falling down into the mantle. This has caused even hotter rock from the aesthenosphere to rise around the 'drip' and replace what is falling away, putting even hotter rock closer to the surface. This heat increases mantle melts and causes more volcanism. Tectonics from active faults like the Hurricane and Toroweap faults and the general uplift of the Colorado Plateau gives magma many paths to the surface. With more research and understanding, the reasons behind the region's excessive volcanism is becoming clearer.
Volcanism on its own is dramatic, but the interaction of lava and water adds an extra level of drama. The Uinkaret volcanic field in GC-Parashant is famous as the source of the 150 lava flows that poured right into the Grand Canyon. Seventeen of them blocked the Colorado River, boiling it away, then damming it. The cooled lava, called basalt, blocked the river and formed huge reservoirs that lasted from a few years to decades, perhaps even a century or more. Remnants of these dams can be seen at places like Whitmore Canyon Overlook in Parashant or Toroweap, in Grand Canyon National Park.
To learn more about the incredible volcanic story of Parashant, use the links below. These pages are an indepth overview of the topic but written for general audiences and students. To put this volcanism in context, see the Geology section of the website for the rest of the geologic story of Parashant over the last 600 million years.
Section 1: Setting the Stage for Volcanism
The Basin and Range Faulting of Parashant
Section 2: What Kind of Eruptions Happen Here?
How Magma Melts and Mixes Below Ground to Influence Eruption Characteristics
Section 3: The Uinkaret Volcanic Field and its Eruptions in Parashant
Recent Eruptions and Lava Flows Dams in the Grand Canyon
Section 4: Timeline of Events for the Most Recent Eruption 950 Years Ago
The Little Springs Eruption near Mt. Trumbull
Last updated: February 18, 2020