Gallery: Obsidian Lava Flows in the Cascades and Long Valley
01cordon-caulle-chile
Cordón Caulle, Chile -------------------- The folks at NASA's Earth Observatory posted [one of the best images of a lava flow](http://earthobservatory.nasa.gov/IOTD/view.php?id=80330) I've seen in a long time this week — it shows the dark [obsidian](http://volcanoes.usgs.gov/images/pglossary/obsidian.php) flow from the [2011-2012 activity at Cordón Caulle](http://stag-komodo.wired.com/wiredscience/2011/06/spectacular-images-and-video-of-the-puyehue-cordon-caulle-eruption-in-chile/) in Chile. The flow is a dramatic feature against the light-colored background of volcanic ash and debris (tephra). The best part of this flow is that according to reports of volcanologists on the ground, the flow is still creeping along even though the eruption has been over for almost a year. I won't spoil the story, so be sure to read the great description of the flow on the NASA EO page linked above. However, you don't need to travel to Chile to see great obsidian flows — flows made of glassy lavas, usually rhyolitic (high silica). The Cascades and Long Valley in the western United States have multiple domes and flows that are fully obsidian or at least partially the glassy, crystal-free lava that is obsidian. I've had a chance to visit a few of these, so I thought we could take a virtual tour of some of the obsidian flows in our national backyard. There are even more than pictured in this gallery, but these here are some of the most striking. *Image: NASA Earth Observatory.*
02panum-crater-california
Panum Crater, California ------------------------ Near the north end of the [Mono Craters](http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-12-) in eastern California, Panum crater is a small rhyolite dome that formed [only around 660 years ago](http://volcanoes.usgs.gov/volcanoes/mono_inyo_craters/mono_inyo_craters_geo_hist_20.html) (the youngest of our western North America obsidian flows). This aerial view of Panum Crater shows the two components of many obsidian flows/domes — the dome itself and the crater formed by some of the initial (and later) stages of dome/flow emplacement. The pile of debris around the edges of the main dome is mostly volcanic tephra caused by explosive eruptions — and the Panum eruption would have [ranked as a VEI 4](http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-12-&volpage=erupt) — while the later dome in the middle is clearly an effusive (lava flow) feature. The dome itself (and some related domes nearby) total about 0.5 cubic kilometer of rhyolitic material. *Image: USGS*
03puffed-obsidian-from-panum-dome
"Puffed Obsidian" From Panum Crater ----------------------------------- This close-up view of some of the rhyolite that makes up Panum Dome shows some of the neat features of glassy volcanic lava. You can clearly see the dark, dense volcanic glass (obsidian) but there are also layers that look lighter and distinctly "puffed" out — these are also made of volcanic glass, but they likely had higher concentrations of gas bubbles, something akin to pumice. As the bubbles expanded when the magma reached the surface and cooler, the layers puffed and cracked like [breadcrust](http://volcanoes.usgs.gov/images/pglossary/breadcrust.php). *Image: Erik Klemetti*
04glass-creek-dome-california
Glass Creek Dome, California ---------------------------- Here is another rhyolitic dome in the [Long Valley](http://volcanoes.usgs.gov/volcanoes/long_valley/) area, this time as part of the [Inyo Chain](http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-13-). There are multiple domes that run roughly north-south along the Sierran front north of the Long Valley Caldera and this is my favorite, Glass Creek, that is draped over a pre-existing ridge. [These were erupting](http://volcanoes.usgs.gov/volcanoes/mono_inyo_craters/mono_inyo_craters_geo_hist_11.html) almost simultaneously with Panum Crater and parts of the Mono chain — roughly 630 years ago. Ash from these eruptions can be found across Nevada as part of [another VEI 4 event](http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-13-&volpage=erupt). Wes Hildreth in [his seminal study of Long Valley](http://pubs.er.usgs.gov/publication/70026744) thinks that the Mono-Inyo chain, although geographically close to the Long Valley caldera, is actually not magmatically related to the giant caldera-forming systems that formed the caldera 740,000 years ago. *Image: Erik Klemetti*
05glass-mountain-california
Glass Mountain, California -------------------------- One set of the obsidian flows I have yet to visit are in and around the [Medicine Lake](http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-02-) caldera. Glass Mountain, Little Glass Mountain, Crater Glass Flow and the Medicine Lake Glass Flow are all rhyolite flows that erupted as [recently as about 950 years ago](http://www.volcano.si.edu/world/volcano.cfm?vnum=1203-02-&volpage=erupt) (for Glass Mountain). Unlike the Mono-Inyo chain, [Medicine Lake](http://volcanoes.usgs.gov/volcanoes/medicine_lake/) is what we call a bimodal volcano — that is, it erupts both low silica basalt and high silica rhyolite — with nothing in between (like andesite). *Image: USGS*
06big-obsidian-flow-newberry-caldera
Big Obsidian Flow, Oregon ------------------------- If we head north, we reach another bimodal caldera that sits behind the main arc of Cascade volcanoes — this time, [Newberry Caldera](http://volcanoes.usgs.gov/volcanoes/newberry/) in Oregon. On the southern wall of the caldera spreading into the caldera itself is the aptly named Big Obsidian Flow that [erupted about 1,320 years ago](http://www.volcano.si.edu/world/volcano.cfm?vnum=1202-11-&volpage=erupt). When this flow was erupted, it produced [pyroclastic flows](http://volcanoes.usgs.gov/volcanoes/newberry/newberry_hazard_61.html) that spread down toward Paulina Lake (and two campgrounds are built on the Big Obsidian Flow deposits). The Big Obsidian Flow is nearly aphyric — meaning you'd be hard pressed to find any crystals in it (and trust me, I've looked at it hoping to get zircon) — meaning it was likely hot when this rhyolite lava erupted, preventing many (if any) crystals from forming in the lava. *Image: USGS*
USGS07sisters77-south-sister-lava-flows-09-77-ann.jpg
South Sister Domes, Oregon -------------------------- [South Sister](http://www.volcano.si.edu/world/volcano.cfm?vnum=1202-08-) is a composite volcano that is part of the Three Sisters volcanic cluster — it is also the youngest and most active, but not from the summit crater. The southern flanks of the volcano are covered in a series of rhyodacite (slightly less silica than rhyolite) domes that are almost obsidian. I say almost because you can actually find crystals in many of these lavas, but it can be challenging. The domes are separated into Rock Mesa and the Devil's Hills Chain. The former likely [erupted roughly 2,350 years ago](http://www.volcano.si.edu/world/volcano.cfm?vnum=1202-08-&volpage=erupt) producing a VEI 4 eruption, while the Devil's Hills were likely erupted about 300 years later and in total are slightly smaller than Rock Mesa (0.3 versus 0.5 cubic kilometers of lava). [Research done on Rock Mesa and the Devil's Hills](http://www.sciencedirect.com/science/article/pii/S0012821X11006339) by colleagues at UC Davis found that many of the zircon crystals in these rhyodacite domes were scavenged from residual magma of rhyolites erupted at South Sister over 20,000 years ago. *Image: USGS*
08obsidian-flow-from-rock-mesa-oregon
Swirling Lava From Rock Mesa, Oregon ------------------------------------ The rhyodacite lavas from Rock Mesa are some of the strangest I've seen, with very glassy carapace (outer layer) than was almost greenish. There was also abundant swirling in the lavas of dense, glassy layers and bubble-rich layers. This betrays the viscous nature of these obsidian (or close) lava flows, where they can deform plastically, yet preserve this deformation as the flow continues to flow and solidify. *Image: Erik Klemetti*
09entrainment-of-material-in-rock-mesa-lava
Clasts Entrained in Obsidian Flows From Rock Mesa, Oregon --------------------------------------------------------- In fact, in some places you can find layers of entrained chunks of other rocks — possibly picked up off the ground surface as the flow was moving — that become incorporated into the flow itself. This layer within a large block of Rock Mesa rhyodacite lava is clearly different material than the dark, dense and glassy lava itself. The taffy-like flow may have flowed over these chunks and they stuck, getting worked into the layer as the flow continued to move. *Image: Erik Klemetti*
10newberry-flow-and-south-sister-oregon
Newberry Flow at South Sister, Oregon ------------------------------------- The largest of the Devil's Hills is the Newberry Flow, the highest up on the flanks of South Sister. In this view, you can clearly see the pressure ridges of the flow and the very steep margin of the flow — you might call this [a coulee](http://stag-komodo.wired.com/wiredscience/2010/03/coulees/). When we were in the valley next to the end of the Newberry flow, you could really get the perspective of the size of it, with walls of 30-plus-foot / 10-meter rubbly lava that meets the glacial lake below South Sister. I do have a standing bet with a friend that the next eruption from South Sister will be another rhyolite eruption, but the [uplift](http://vulcan.wr.usgs.gov/Volcanoes/Sisters/WestUplift/information_statement_08may2001.html) that got us all excited about 12 years ago has [slowed to a barely noticeable pace](http://www.registerguard.com/web/updates/29402840-55/bulge-sister-south-scientists-volcano.html.csp). *Image: USGS*
