America's Volcanic Past
|"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994|
Volcanic Highlights and Features:
|[NOTE: This list is just a sample of various Death Valley features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of Death Valley.]|
The oldest rocks exposed in Death Valley are about 1.8 billion years
almost half the age of the Earth. These venerable rocks are the remnants of an
ancient volcanic mountain belt with its flanking deposits of mud and sand.
At about 1.8-1.7 billion years ago, these
volcanic and sedimentary rocks were severely
metamorphosed -- altered, recrystallized, and partially
remelted by the Earth's internal heat and by the load of overlying younger rocks.
The original rocks were transformed to contorted schist and gneiss,
making their original parentage almost unrecognizable.
At about 1.4 billion years ago, the metamorphic complex was injected with dikes
and larger blobs of
During Late Paleozoic and Mesozoic time (225 - 65 million years ago),
the Death Valley landscape changed dramatically. The quiet, sea-covered
continental margin was replaced by erupting volcanoes, uplifting mountains,
compressional thrusting. These changes were brought about by a tectonic collision to the west.
The western edge of the North American continent was pushed against
the oceanic plate under the Pacific Ocean. A deep trench formed, and the
Pacific oceanic plate began to sink (subduct) beneath the more
buoyant continental rock of North America. A chain of volcanoes pushed
through the continental crust parallel to the deep trench,
fed by magma rising from the subducting oceanic plate as it entered
Earth's hot interior. Thousands of feet of lavas erupted,
pushing the ocean over 200 miles to the west. The Death Valley region
was no longer coastal real estate, as it had been for the previous billion years.
Most of the volcanic activity was centered just to the west of Death Valley,
although some of the oldest Mesozoic rocks are exposed in the southern Panamint Range.
The deep magma chambers feeding the volcanoes eventually cooled and solidified,
forming the granites widely exposed in the Sierra Nevada Mountains.
A few of these granitic bodies intruded the Panamint and Cottonwood Mountains,
but these rocks are not easily accessible. One of these relatively small
granitic plutons emplaced 67-87 million years ago, right near the end of the
Mesozoic Era, spawned one of the more profitable precious metal deposits
in Death Valley, giving rise to the town and mines of Skidoo (although
these gold deposits were quite small compared to the larger California
goldfields west of the Sierra Nevada Mountains).
Death Valley itself was a broad, mountainous region during this time.
Mountains are mostly sites of erosion, not deposition, and the sediments
worn off the Death Valley region were shed both east and west carried by
wind and water; the eastern sediments which ended up in Colorado are now
famous for their dinosaur fossils.
After 150 million years of volcanism, plutonism, metamorphism, and
thrust-faulting had run their course, the early part of the Cenozoic Era
(early Tertiary, 65-30 million years ago) was a time of repose.
Neither igneous nor sedimentary rocks of this age are known here.
No great events were recorded here, simply the weathering away of the
region to a rolling landscape of low relief.
Beginning in Miocene time, the geologic tranquility was shattered.
Volcanism and faulting started up again, but this time caused by extension
in the crust rather than compression. The birth of the Death Valley
landscape familiar to us today was beginning.
Excerpts from: USGS/NPS Geology in the Parks Website, August 2001
|Death Valley National Park|
The face of the Black Mountains along Artist's Drive is made up of the multicolored rock of the Artist Drive Formation. Aprons of pink, green, purple, brown, and black rock debris drape across the mountain front, providing some of the most scenic evidence of one of Death Valley's most violently explosive volcanic periods. The Artist Drive formation is made up of cemented gravel, playa deposits, and much volcanic debris, perhaps 5,000 feet thick.
The steep face of the Black Mountains is made up of some of the oldest rocks in Death Valley. These 1.7 billion-year-old Precambrian rocks are the remnants of an ancient volcanic mountain belt with flanking deposits of mud and sand.
8,000 feet of metasediments and volcanics.
Split Cinder Cone:2
Less than 300,000 years ago, a chamber filled with solid crystals and searing molten basaltic rock simmered beneath Death Valley. Magma rose toward the surface, following weaknesses in the Earth's crust. Nearing the surface, the black lava encountered the fractured earth of the Death Valley Fault zone. Lava quickly made its way through the fault-weakened rock and burst out of the valley floor as a fiery fountain of scorching lava and gas. Lava fountains threw blobs of molten basalt hundreds of feet into the air. Although lava erupted at 1200 degrees C (2200 degrees F), most of the molten, airborne globs cooled and solidified to form cinders before reaching the ground. Most cinders fell very near the central vent, building a small cone. Split Cinder Cone was probably built over a very short time; its birth and death probably spanned less than a few decades. Although the little volcano lay quiet, the Death Valley Fault zone continued to move as it had for almost three million years. The wrenching force of this very active fault pulled one part of the volcano to the southeast, while the other part was pulled toward the northwest. Eventually, the crust could no longer resist the wrenching motion of the fault and the cinder cone began to be ripped into two pieces. Each time the fault moved, the two sides of the cone moved farther apart.
Less than 10,000 years ago over a dozen volcanoes dot the landscape of Ubehebe volcanic field. Ubehebe Crater is the largest and youngest volcanic feature. Following weaknesses in the Earth's crust, searing basaltic magma rises upward. A fault along the base of Tin Mountain, responsible for uplift of the entire mountain range, lies in the path of the molten mass, providing an easy escape route to the surface. Magma worked its way through the fault-weakened rock where it met water-soaked bedrock and alluvial fan sediments. In an instant, water flashed to steam. A sudden, violent release of steam-powered energy blasted away the confining rock above. The largest of these eruptions produced Ubehebe Crater, over a half a mile wide and 770 feet deep. The eruptions that created Ubehebe Crater blasted through older conglomerate layers, now revealed in the crater walls. Over a dozen other explosion craters and tuff rings in the Ubehebe Crater field are the result of this type of hydrovolcanic eruption.
Willow Spring Pluton:1
The steep face of the Black Mountains is made up of some of the oldest rocks in Death Valley. These 1.7 billion-year-old Precambrian rocks are the remnants of an ancient volcanic mountain belt with flanking deposits of mud and sand. About 1.8-1.7 billion years ago, these volcanic and sedimentary rocks were severely metamorphosed, altered, recrystallized, and partially remelted by the Earth's internal heat and by the load of overlying younger rocks. The original rocks were transformed to contorted gneiss, making their original parentage almost unrecognizable. 11 million years ago, these venerable rocks were injected with magma that solidified to form the Willow Spring pluton. The diorite to gabbro composition of the Willow Spring pluton blends well with the dark Precambrian gneiss, so you'll have to look carefully to see the contact between the two rock types.
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