Newberry Volcano

For a Google Earth .kmz file to explore Newberry Caldera and the surrounding landforms, scroll to the very bottom of the page.

Here is a volcano you might not know anything about. Its name is Newberry Volcano and it rises about 4000ft above the city of Bend, Oregon (Donnelly-Nolan et al., 2011). The volcano is actually nestled between several towns, but is hard to give an exact location because of its size and the various lava flows that is has erupted. It is located most closely to La Pine, fairly close to Sunriver, and near Bend, Oregon. And there are really two parts to this volcano to take into consideration. The volcano dimensions are 75 miles long in the north-south direction and 27 miles wide in an east-west direction (2011). The volcano, though, is hard to truly make out because the flanks of the volcano are not like the others found in the Cascade Volcanic Arc. The sides are shallowly sloped because, unlike the composite cones of the Three Sisters volcanoes and Mt. Bachelor very near Newberry Volcano, Newberry is a shield volcano. What this means is that the flanks of the volcano have been built up by basalt, and basalt is low viscosity lava. Low viscosity lavas tend to flow much more easily, and don’t mound up like those lavas that erupted from other nearby volcanoes. Instead, it flows down the side of the volcano fairly easily creating an upside down dinner plate shape (or shield, get it?).

The other feature, which more people could probably point out, is the volcano’s caldera. A caldera is just a really big crater formed from the collapse of the vent of a volcano. Newberry’s caldera is about 4 miles by 5 miles, so it’s a pretty big hole (http://volcanoes.usgs.gov/volcanoes/newberry/newberry_geo_hist_85.html). There are two lakes present in the caldera, Paulina Lake (pronounced Pa-line-a) and East Lake. These two lakes are separated by the Central Pumice Cone, which has been dated at approximately 7,200 years old (its formation happened a little while after the formation of Crater Lake and can be dated because of the presence of related ash) (Jensen and Chitwood, 2000). Also, within this volcano is a feature called the Big Obsidian Flow. This particular flow was part of a group of eruptions called the Big Obsidian Eruptive Episode. This included quite a few explosive eruptions that culminated in the final eruption known from Newberry, the Big Obsidian Flow. These later eruptions show Newberry Volcano to be a bimodal volcano, or a volcano that emits mainly basaltic eruptions on its flanks and more rhyolite volcanic activity dominates the eruptions within the caldera (another good example of bimodal volcanism would be from the Yellowstone Hotspot). This final eruptive period began 1580 years ago with explosive eruptions of pumice falls from a vent near the southern Caldera wall (2000). 250 year later an ash flow occurred and the final eruption from this vent was the obsidian flow. The progression of these events, from basalt to rhyolite, shows us that that the volcano was degassing, leaving us with those final stages of silica-rich lavas, like obsidian. Obsidian flows usually mark the end of an eruption phase.

Obsidian is a very cool rock, both in temperature and characteristics. Unlike other rocks, it contains very few crystalline minerals, meaning there is no crystalline lattice here, no order like the components seen in other rocks. The other rule that obsidian doesn’t follow is that it is felsic but is dark in color, unlike most other felsic rocks. That is confusing to most people, why is it black and still considered felsic? Well, the term felsic really pertains to the composition of the rock, felsic meaning that the rock is rich in silica. And in the case of obsidian, it contains ≥70% silica, which is a lot. The dark color that is seen in obsidian is thought to a result of the glass being tinted by impurities (things that aren’t silica) present during obsidian’s formation (see Figure 2). So, why are there no mineral crystals present in obsidian? Well, there are a few explanations out there. First, most people say that obsidian cools very quickly, too quickly to form those perfect crystalline bonds that are seen in minerals. So a glassy texture develops because the lava flowing is already below its crystallization temperature, and the resulting rock formed has ions that cannot arrange themselves into a perfect, repetitive lattice. The other explanation has to do with the flow of obsidian. Considering the thicknesses of some obsidian flows, there is no way that the entire flow could have cooled quickly (see Figure 3). As a result, some suggest that the very slow flow of viscous obsidian prevents the crystallization of minerals (Winters, 2001). So, there is still some debate about its formation but that doesn’t make it any less amazing of a rock. Though the Big Obsidian Flow is probably one of the most visited sites within the caldera of Newberry Volcano, there are numerous other volcanic features that can be visited that are a result of Newberry eruptions outside of the caldera. The various landforms and formations associated with Newberry are all over the place south of Bend and here are a few of note. Before getting to the Caldera drivers along Highway 97 will come across Lava Butte, one of 400 cinder cone vents that dot Newberry’s flanks and this cinder cone is perhaps the most accessible (see Figure 4). There you can visit the Lava Lands Visitor Center of the Newberry National Monument as well as take a spin around an a’a flow with all of the features you would expect, like accretionary lava balls and lava channels.

The lava flow associated with the eruption of lava Butte also stretches in a northerly direction towards the Deschutes River causing the flow of the river to be permanently displaced around the margins of the lava flow. The other features that are probably some of the most exciting that are a result of basalt flows along the flanks of Newberry are the various lava tubes that people can explore. These subterranean caves can be easily accessed from basically 2 places; the most travelled is the Lava River Cave outside of Sunriver and the others are on China Hat Road in the very southern part of the city of Bend. All of these caves are associated with basaltic eruptions from Newberry’s flanks and show cave features like lavacicles, step marks and cauliflower a’a lava (probably not the true name, but it really does look like cauliflower).

Though Newberry Volcano is not currently “active”, meaning not currently erupting, there are global positioning systems (GPS) receivers and seismic stations that are constantly monitoring the volcano to note any changes that occur in activity. Small magnitude earthquakes occur every once in a while but no great threats have been seen from the volcano within historical times. However, if Newberry Volcano were to erupt in our lifetime, geologists presume the likely hazards would be lava flows along the volcano flanks, tephra from either a smaller vent on the flank or a larger eruption from the caldera, pyroclastic flows from the caldera, and earthquakes and faulting leading up to an eruption and even occurring after a catastrophic eruption (Donnelly et al., 2011).