Big Bend National Park is a geologist's dream -- or nightmare. There is so much to study here, where do you start?
Much of the park was covered many times with lava flows, and experiences cataclysmic eruptions and earthquakes. See: (
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Goat Mountain is one of the famous mountains in the park, and was formed as a result of volcanic eruptions long ago.
Two signs along the Ross Maxwell Scenic Drive explain:
"GOAT MOUNTAIN
Some 29,000,000 years ago, volcanoes dominated the ancient Big Bend. Many of the formations along the Ross Maxwell scenic Drive, including Goat Mountain, originated in this volcanic past. A new theory (diagrams below) tells a tale of fiery explosions and massive volcanic domes.
[graphic]
An initial large explosion created a crater with an older, layered volcanic rock. Possibly the explosion occurred when rising magma (molten rock beneath the Earth’s crust) came into contact with water trapped in the older lava, causing it to flash into steam.
[graphic]
Silica rich magma continued searching upward, causing repeated pyroclastic eruptions (a mixture of superheated gas, ash, and rock fragments). The flows partially filled the crater, informed a collar of steaming volcanic material around the vents. Similar pyroclastic material is visible at Tuff Canyon and Burro Mesa Pouroff.
[graphic]
Over time, the gas content of the magma decreased, and the final eruptions produced thick slow, slow moving silica rich lava (magma that reaches the surface). The lava form thick domes that were higher than, and spread over, the crater walls. A dozen or so similar volcanic domes of dotted the landscape between Burro Mesa and Castolon.
[graphic]
About 27 million years ago, the region was uplifted and faulted and erosion began to shape the land we see today. The overlying silica rich lava was resistant to erosion and form steep, jointed cliffs. The weaker car pyroclastic deposits below or eroding away, exposing a dike (magma intrusion) that may represent part of the original magma feeder system."
"FINS OF FIRE
The spines of dark rock marching across the desert floor are called dikes. Contemporaries of the Chisos Mountains, these outcrops are evidence of the most recent igneous activity in the area. Like great stone fences, dikes can be traced for miles across the park - reminders of the molten world beneath the quiet desert surface."