Obsidian Flow at the Newberry Caldera
La Pine, OR - Sat, 14 Sep 2019, 7:45pm
"There's a national monument we'll be driving right past? That we've never been to before?" was our discussion in the car as we headed up into the Cascades Saturday afternoon. It's the Newberry National Volcanic Monument. It seemed like we'd have to go! Yet it was odd that we'd been past it at least twice before and somehow chose not to stop either time. Could it have been that we looked up trails there and didn't find anything interesting? Hawk looked it up in our guidebook as we drove and found at least two interesting trails. We'd have to go! Thus we sped onward from our hike at Salt Creek Falls earlier in the afternoon to get to Newberry before dusk.
Indeed it was close to sunset as we reached the trailhead inside the huge caldera of this ancient volcano. Fortunately it was a short trail, looping around atop an obsidian flow. An easy, paved trail led to the base of the flow; then wooden stairs led up the steep side.
The obsidian flow here is similar to what we encountered at Glass Mountain in northern California two weeks earlier. In fact for that reason we almost chose not to do this hike; we figured we were "lava'ed out" this month. But I'm glad we came as trail felt more remote while the mountain seemed more manageable in size. In the picture above it may seem downright small- like that's a puddle and a fern in the photo- but the obsidian flow is about 100 feet tall there and up to 200 feet tall elsewhere. That puddle is actually a small lake.
The rocks are the result of a lava flow from about 1,300 years ago. They're a combination of obsidian and pumice. Both are primarily silicon dioxide (SiO2) - the material commonly referred to as glass. But why aren't they clear like glass?
For pumice, the answer is bubbles. Bubbles of gas are trapped in the molecular structure of the silicon dioxide, preventing it from being translucent. In the lighter colored pumice the bubbles are tiny; darker pumice results when the bubbles are larger.
Obsidian is solid glass. It has no bubbles. So why isn't it clear? The answer for obsidian is that it contains a small amount of magnetite (iron dioxide) that gives it the black color.
Very little of the rock in this flow is obsidian. In general it's extremely rare, as it only forms in lava flows like this. Natives who lived in this area prized the obsidian for its effectiveness in forming tools. Obsidian knives and arrowheads, for example, could be made very sharp and held their edges well. Obsidian was a valuable trade good and thus a source of wealth for people who lived in this region.
The trail around the top of the flow led us to a nice view of Paulina Peak in the distance. Paulina Peak is volcanic but it's not the center of the volcano. It's the edge! The ancient volcano here is the size of the state of Rhode Island. We're in the caldera, the sunken inside of the cone. This caldera is several miles across.
Also inside the caldera are not one but two large-ish lakes. In the distance above is Paulina Lake, the larger of the two. Beyond it you can see the far rim of the caldera.
I'm glad we chose to come out here. And I'm glad we're here at sunset. It's actually a very nice time of day with beautiful light. The one downside is there's a second hike out here in the caldera we'd like to do- but won't have time for. We may have to truck back out here from Bend Sunday morning.
"There's a national monument we'll be driving right past? That we've never been to before?" was our discussion in the car as we headed up into the Cascades Saturday afternoon. It's the Newberry National Volcanic Monument. It seemed like we'd have to go! Yet it was odd that we'd been past it at least twice before and somehow chose not to stop either time. Could it have been that we looked up trails there and didn't find anything interesting? Hawk looked it up in our guidebook as we drove and found at least two interesting trails. We'd have to go! Thus we sped onward from our hike at Salt Creek Falls earlier in the afternoon to get to Newberry before dusk.
Indeed it was close to sunset as we reached the trailhead inside the huge caldera of this ancient volcano. Fortunately it was a short trail, looping around atop an obsidian flow. An easy, paved trail led to the base of the flow; then wooden stairs led up the steep side.
The obsidian flow here is similar to what we encountered at Glass Mountain in northern California two weeks earlier. In fact for that reason we almost chose not to do this hike; we figured we were "lava'ed out" this month. But I'm glad we came as trail felt more remote while the mountain seemed more manageable in size. In the picture above it may seem downright small- like that's a puddle and a fern in the photo- but the obsidian flow is about 100 feet tall there and up to 200 feet tall elsewhere. That puddle is actually a small lake.
The rocks are the result of a lava flow from about 1,300 years ago. They're a combination of obsidian and pumice. Both are primarily silicon dioxide (SiO2) - the material commonly referred to as glass. But why aren't they clear like glass?
For pumice, the answer is bubbles. Bubbles of gas are trapped in the molecular structure of the silicon dioxide, preventing it from being translucent. In the lighter colored pumice the bubbles are tiny; darker pumice results when the bubbles are larger.
Obsidian is solid glass. It has no bubbles. So why isn't it clear? The answer for obsidian is that it contains a small amount of magnetite (iron dioxide) that gives it the black color.
Very little of the rock in this flow is obsidian. In general it's extremely rare, as it only forms in lava flows like this. Natives who lived in this area prized the obsidian for its effectiveness in forming tools. Obsidian knives and arrowheads, for example, could be made very sharp and held their edges well. Obsidian was a valuable trade good and thus a source of wealth for people who lived in this region.
The trail around the top of the flow led us to a nice view of Paulina Peak in the distance. Paulina Peak is volcanic but it's not the center of the volcano. It's the edge! The ancient volcano here is the size of the state of Rhode Island. We're in the caldera, the sunken inside of the cone. This caldera is several miles across.
Also inside the caldera are not one but two large-ish lakes. In the distance above is Paulina Lake, the larger of the two. Beyond it you can see the far rim of the caldera.
I'm glad we chose to come out here. And I'm glad we're here at sunset. It's actually a very nice time of day with beautiful light. The one downside is there's a second hike out here in the caldera we'd like to do- but won't have time for. We may have to truck back out here from Bend Sunday morning.