Pisgah crater
The first place we went to was Pisgah crater. Pisgah crater is off hwy 40 about 40 miles southeast of Barstow. The crater and cinder cone are very young, under 100,000 years old. Cinder cones usually only erupt once, another eruption will form a separate cone, in this way, large clusterings of cinder cones can form, like the one in the northern Mojave with over 40 cinder cones streatching over 26,000 acres.
Pisgah crater is off on its own, 30 miles northwest of the next cider cone, Amboy crater. Pisgah is easy to get too. A quarry road leads half way up the cinder cone, and is surrounded by 10 miles of lava flow.
No one is quite sure why these cinder cones form in the desert. They are made of basalt magma. Basalt is what makes up the islands of Hawaii. It is typified by a dark appearance (mostly black with some red or gray), very low viscosity, and mild, flowing, eruptions. The eruption first throws out tephra, a porous rock heavier than pumice, which builds the cone. After the volcano is done erupting tephra, a lava flow begins. The tephra cone isn't strong enough to support a tube of magma, so it flows out of the bottom of the cone.
the view of the cinder cone about half way up
Me inside the crater
View from the summit. I believe those mountains mark the boundary of the Mojave National Park (train for scale)
View of the lava fields from the summit (truck for scale)
We found this rock while descending the cone. Not exactly sure how the different colors formed.
This is a pressure ridge. Flowing lava underneath the outer layer of cooling lava caused the outer layer to crack open. I believe the pressure of the steam from the lava beneath it is the main cause of this. In some cases, it won't burst, leaving a bubble of cooled lava (unfortunately, I didn’t see any of these)
This neat piece of volcanic rock was found near another, larger, pressure ridge that collapsed when the pressure was released. I think what happened here was, two pieces of the cooling lava fell just right, so that they fused together in this way. The whole in the center is probably where a steam/gas bubble escaped. Notice how jagged the inside of the rock is in comparison to the outside. The inside rock is called aa, named by the Hawaiians because it hurt to walk on.
Another shot of aa
Pahoehoe is a common occurrence along pressure ridges. It occurs when the flowing lava bumps up against an obstacle. The lava then bunches up, causing this rope like surface. Pahoehoe is the Hawaiian word for “rope”. It is exactly the same make up as aa, just with less gas content.
“squeeze out” also happens along pressure ridges. This is where that hot lava oozes out from cracks in the cooling lava.
My dad helping to be the scale for this crack we found in the lava field. Looks to be fault related.
Looking back up at the cinder cone from the lava field (truck for scale)
Pisgah crater is off on its own, 30 miles northwest of the next cider cone, Amboy crater. Pisgah is easy to get too. A quarry road leads half way up the cinder cone, and is surrounded by 10 miles of lava flow.
No one is quite sure why these cinder cones form in the desert. They are made of basalt magma. Basalt is what makes up the islands of Hawaii. It is typified by a dark appearance (mostly black with some red or gray), very low viscosity, and mild, flowing, eruptions. The eruption first throws out tephra, a porous rock heavier than pumice, which builds the cone. After the volcano is done erupting tephra, a lava flow begins. The tephra cone isn't strong enough to support a tube of magma, so it flows out of the bottom of the cone.
the view of the cinder cone about half way up
Me inside the crater
View from the summit. I believe those mountains mark the boundary of the Mojave National Park (train for scale)
View of the lava fields from the summit (truck for scale)
We found this rock while descending the cone. Not exactly sure how the different colors formed.
This is a pressure ridge. Flowing lava underneath the outer layer of cooling lava caused the outer layer to crack open. I believe the pressure of the steam from the lava beneath it is the main cause of this. In some cases, it won't burst, leaving a bubble of cooled lava (unfortunately, I didn’t see any of these)
This neat piece of volcanic rock was found near another, larger, pressure ridge that collapsed when the pressure was released. I think what happened here was, two pieces of the cooling lava fell just right, so that they fused together in this way. The whole in the center is probably where a steam/gas bubble escaped. Notice how jagged the inside of the rock is in comparison to the outside. The inside rock is called aa, named by the Hawaiians because it hurt to walk on.
Another shot of aa
Pahoehoe is a common occurrence along pressure ridges. It occurs when the flowing lava bumps up against an obstacle. The lava then bunches up, causing this rope like surface. Pahoehoe is the Hawaiian word for “rope”. It is exactly the same make up as aa, just with less gas content.
“squeeze out” also happens along pressure ridges. This is where that hot lava oozes out from cracks in the cooling lava.
My dad helping to be the scale for this crack we found in the lava field. Looks to be fault related.
Looking back up at the cinder cone from the lava field (truck for scale)
posted by Life Saver at 8:37 AM
1 Comments:
Hi
Interesting account and photos. Nice to make a trip like that with your dad. I was recently past Pisgah crator on the way home from Meteor Crater ... now I'm anxious to return and explore ... Thanks!
rbruns@napavalley.edu
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