The City of Rocks National Park in New Mexico is a geological marvel. The rock formations were caused by a VERY large volcanic eruption – 1000 times larger than Mount Saint Helens eruption on May 18, 1980. Even though we lived thousand of kilometers away, I remember wiping away centimeters of ashy dust from my parked vehicle over the space of a week or two when Mount Saint Helen’s blew its top, and that explosion happened quickly. The volcanic eruptions that formed the City of Rocks would have taken months to years to subside and would have left the sky darkened and the air unbreathable for a long time.
Those who study such things say the magma that produced the eruption was probably 6 to 15 km (3.7 to 9.3 miles) below the earth’s surface. A conduit formed between the molten magma and the earth’s surface allowed the magma to escape through a volcanic vent. They believe the main phase of the eruption was the most violent and began forming what is commonly known as the Kneeling Nun Tuff, of which the City of Rocks is part. They calculate that close to 240 CUBIC MILES of volcanic pumice, ash and gas rained out of the sky. As the volcano’s vent blew wider more and more magma spewed forth allowing increasing amounts of volcanic material to erup quickly and then move as a large, hot, turbulent cloud depositing volcanic material as far as 200 km. (125 miles) away. Imagine throwing rocks the size of those in the City of Rocks for 200 kms! But it did just that in what geologist cal the “Ignimbrite eruption” phase. When this very hot material fell, it compacted to form the dense rocks of the City of Rocks and others in the surrounding areas. The residual heat from the magma ws so hot it produced thermal areas and hot springs like Yellowstone National Park and even on just down the road from the City of Rocks.
The columns, or pinnacles, of rocks the City of Rocks likely were deposited after the main explosion. These massive columns are heavily pitted and although they look like separate rocks, I scratched the soil and found it had little depth before reaching solid rock. This must be why the desert is so dangerous in a rainstorm. The water has no place to go other than in a quick moving, dangerous wash area.
When these columns started cooling, cracks formed perpendicular joints to the ground surface. The cooling joints widened by erosion caused by freezing and thawing and wind that also allowed vegetation to take hold. The vegetation put down roots and along with vegetative acids widen the cracks even further. Eventually the erosion processes striped finer sized material from the rocks and produced the material that covers the desert floor with a rock dense sand. In times of high wind, dust storms close down highways, cover everything in a fine grit and must make breathing difficult.
The desert around the City of Rocks is a beautiful place with its own charm, but I’m beginning to think it has bi-polar tendencies. The days can be searing hot and the nights bitter cold, and the vegetation that grows in abundance is appealing to the eye, but prickly and sharp to the touch. It’s a landscape very different from my native home within the Boreal Forest, but one in which the majesty, creativity and power of God is bare for all to see and experience.