The state of Oregon contains about a dozen active volcanoes. These active volcanoes include Mount
Hood and Mount Jefferson. However, not all of the volcanoes within the state are tall
stratovolcanoes. One of these lesser known volcanic fields is located in a sparsely
populated portion of Lake County, and is adjacent to two other recent volcanic fields. What I am
referring to is the Devils Garden volcanic field. This video will discuss this active volcano,
and mention what its future hazards are. The Devils Garden volcanic field can be found in
the south central portion of Oregon. Specifically, it is 23 miles southeast of the Newberry
Volcano and 10 miles northeast of Fort Rock. Within 15 miles of this volcano are two other
massive lava flows. All of these regional eruptions are part of the so-called high
lava plains in southern Oregon. These volcanoes exist due to a mechanism known as slab rollback.
Underneath Oregon, the Juan de fuca plate is being subducted underneath the north American plate.
The subducted crust from this collision then migrates upwards, creating the cascade volcanoes.
However, these 3 volcanoes are NOT part of the cascade range. For an unknown reason,
the portion of the subducted Juan de fuca plate has recently driven downwards at a much steeper
angle. This caused material deep in the mantle to rise upwards and fill the void,
which caused a number of basaltic eruptions. The Devils Garden volcanic field contains
a vast field of a basaltic lava variety known as pahoehoe, which forms ropy masses.
This lava covers covers a vast area, which totals approximately 45 square miles. Interestingly,
all of this lava is believed to have formed in a single eruption. We have not been able
to definitively date when this eruption occurred, but current evidence suggests that it took place
sometime between 15,000 and 20,000 years ago. This eruption began in the northeast portion
of the current lava field. Initially, effusive lavas erupted from a 2 mile long fissure which
was around 4900 feet in elevation. The lava which erupted was very fluid due to its low
silica content, and moved several miles per hour. Lavas flowed outwards in every direction,
but preferentially travelled to the southwest as gravity naturally carried it in that direction.
As lavas continued to flow downhill, a new vent opened up a mile to the south. This vent formed
two small cinder cones which climbed to 60 and 70 feet above the surrounding landscape.
Eventually, lavas stopped erupting from this vent, and drained out from underneath
to erupt elsewhere. This caused the center of the two cones to partially collapse, thus
giving these features the name "the blowouts". This effusive eruption continued for several
years, causing lava to reach more than 9.5 miles away. Eventually, this eruption slowly came to a
conclusion. As nearby lava drained back into the fissure it originated from, it formed a feature
known as a rampart. Once the lava tubes which fed the eruption were completely absent of molten
rock, they either collapsed under the weight of overlying rock OR formed a series of caves. Today,
several of these caves can be explored if you have proper equipment. The most
well known of these caves is called Derrick's Cave, from which a photo is shown on screen.
Although no eruptions have occurred since, this Devils Garden volcano could erupt once again.
A future eruption, although unlikely, would produce additional fissures of basaltic lava
which would slowly spread out over a wide area. Such an eruption would not necessarily
occur over this existing lava field, but rather somewhere within 20 miles of the Devils Garden.
This type of eruption would pose two hazards, in addition to the danger of slow moving lava flows.
Although the 3 eruptions which have historically occurred in the region have NOT been explosive,
this could change during if lava came into contact with groundwater. This could cause
a phreatic eruption, and throw boulders up to a few miles. The second hazard to note is that this
type of eruption produces lots of toxic gasses, such as carbon dioxide and sulfur dioxide. Both
of these gasses are heavier than air, and could travel downhill where it could cause asphyxiation.
As a result of these hazards, the US geological survey designated the Devils Garden volcanic
field as a very low threat volcano. I hope that you enjoyed this video.
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