Rocks that Float and a Mountain of Glass
Modoc National Forest, CA - Mon, 2 Sep 2019, 11am
"Rocks that float and a mountain of glass" is how Glass Mountain in Modoc National Forest was described many years ago. With a name like Glass Mountain, let alone a description like that, we knew we had to see it. It was a few miles off the paved roads, no problem in our 4x4. The trail even showed that it was previously drivable, though now blocked off.
Glass Mountain is another dried lava flow, the remnant of lava that coursed out of a vent nearby. Rocks are piled in chaotic jumbles. If it weren't for the sparse small trees and the blue sky overhead you could imagine this as an alien landscape.
What's fascinating about Glass Mountain is the sheer size of it. The plateau we're on is at least a mile across... and it's 1000 feet high! And that taller mountain in the distance is also volcanic.
From the description, "Rocks that float" refers to pumice. Pumice is a type of volcanic rock. It's formed from molten silicon dioxide that solidies around small gas bubbles during a volcanic explosion. Those gas bubbles make the rock's density low enough that it floats in plain water. Most of the rock in this mountain is pumice... so this mountain would literally float... if there were enough water here. (On a much smaller scale, you could take a rock and throw it in a pond to see it float; though removing rocks from this area is illegal.)
"Mountain of glass" refers to obsidian, a black, smooth rock that forms from lava under the right conditions. Obsidian, like pumice, is also primarily silicon dioxide- i.e., glass! Where it cooled without major impurities it has the glossiness of glass.
We did see veins of obsidian shooting through many of the rocks at Glass Mountain. Though not enough that I'd choose to name the whole mountain for it. Mostly (99%+) it's pumice. So maybe call it Floating Mountain instead. 😉
"Rocks that float and a mountain of glass" is how Glass Mountain in Modoc National Forest was described many years ago. With a name like Glass Mountain, let alone a description like that, we knew we had to see it. It was a few miles off the paved roads, no problem in our 4x4. The trail even showed that it was previously drivable, though now blocked off.
Glass Mountain is another dried lava flow, the remnant of lava that coursed out of a vent nearby. Rocks are piled in chaotic jumbles. If it weren't for the sparse small trees and the blue sky overhead you could imagine this as an alien landscape.
What's fascinating about Glass Mountain is the sheer size of it. The plateau we're on is at least a mile across... and it's 1000 feet high! And that taller mountain in the distance is also volcanic.
From the description, "Rocks that float" refers to pumice. Pumice is a type of volcanic rock. It's formed from molten silicon dioxide that solidies around small gas bubbles during a volcanic explosion. Those gas bubbles make the rock's density low enough that it floats in plain water. Most of the rock in this mountain is pumice... so this mountain would literally float... if there were enough water here. (On a much smaller scale, you could take a rock and throw it in a pond to see it float; though removing rocks from this area is illegal.)
"Mountain of glass" refers to obsidian, a black, smooth rock that forms from lava under the right conditions. Obsidian, like pumice, is also primarily silicon dioxide- i.e., glass! Where it cooled without major impurities it has the glossiness of glass.
We did see veins of obsidian shooting through many of the rocks at Glass Mountain. Though not enough that I'd choose to name the whole mountain for it. Mostly (99%+) it's pumice. So maybe call it Floating Mountain instead. 😉