Volcanoes in eastern Oregon are a great geologic road trip.

Doc,
I see that volcanoes are your field of interest. I'm a self-professed volcano nut, and I'm already planning next spring's road trip, maybe to the High Lava Plains of eastern Oregon. The name alone is intriguing! I have heard there are some little cinder cones way out there. What do you know about them? Been there? Worth the visit?
Denise Hodgkins,
Port Angeles, WA

Denise,
There are indeed some young-looking cinder cones and lava flows in eastern Oregon. I think you are referring to Jordan and Diamond Craters. I've been to both areas, and they are definitely worth the visit.



Coffee Pot cone in the far distance.

The Jordan Craters are in the southeast corner of the state, off Highway 95 near the town of Jordan Valley. There a number of cinder cones and lava fresh lava flows- they look as if they erupted yesterday (read about cinder cones in my first-ever Doctor Rock post). However, radiocarbon dates indicate that the most recent eruption, at Coffee Pot Crater, was 3200 years ago. Until usable material for radiocarbon carbon dating was found, this cone was widely held to be only 1-200 years old. It is the only cone in the Jordan Craters accessible by road. Here is a map
http://www.blm.gov/or/resources/recreation/googlemap.php?lat=43.14588&lng=-117.4588
use the 'satellite' tab in the upper right to see topography. The lava flows are the dark areas. Coffee Pot erupted 30 square miles of basalt lava.
The area is administered by BLM. The round trip to the single road accessible cinder cone, Coffee Pot Crater, is 52 miles. The roads are not paved. Be wary. It's not a good idea to take a big rig in there. When I was there in the spring, snow had just melted and roads were a quagmire. I barely made it back out of there in my all-wheel-drive Forester. Pay attention to the weather, and only go after the roads have had a chance to dry out. It is remote country- no services, poor cell coverage, no help. Be smart.
There is a great route guide here: http://www.everytrail.com/guide/birch-creek-ranch-jordan-craters
The Global Volcanism Program (a must-visit site for you volcanophiles out there) has sparse information about the Jordan Craters here: http://www.volcano.si.edu/volcano.cfm?vnum=1202-19.
A pamphlet (a bit dated, from 1977) explains some of the detailed geologic features you can see in the Jordan Craters: http://www.oregongeology.com/pubs/og/OBv39n08.pdf

This is Little Red cone in the Diamond Craters.

The other place is the Diamond Craters, 40 miles southeast of Burns and Malheur Lake. The essential info is on this great website for volcanophiles: http://volcano.oregonstate.edu/diamond-craters. There are about a dozen vents in the area, and a signed nature trail takes you to many of the points of interest. The oldest cone is maybe 60,000 years old, but the youngest is a meer 6,000 or so. While you are in the area, consider traveling the Diamond Loop Back Country Byway, a 67-mile unpaved back-country drive. Well worth it!



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What's the difference between the Sierra and Cascade Mountains?

Dear Doctor Rock,

Why do we call the mountain range in California 'The Sierra Nevada' and the ones in Oregon and Washington 'The Cascades'? What is the difference?

Rita Bjornstein,
Topeka, Kansas

Dear Rita,
They are two geologically and geographically separate mountain ranges. The Sierra Nevada (the 'Snowy Range') are older than the Cascades, and were once volcanic. Between about 220 and 15 million years ago, there was subduction off the coast of California- the now-extinct Farallon Plate slid beneath the west-moving North American Plate, and a range of volcanic mountains rose where the Sierras are. The famous granite of Yosemite, Mount Whitney, and elsewhere in the Sierras was once the magma in the crust that fed those volcanoes. Subduction migrated northward up the coast of the continent, and the volcanic rocks that once covered the surface in the Sierras are mostly stripped away by erosion to expose the guts of the silenced volcanoes.
The Cascades are still an active volcanic chain and result from subduction of the Juan de Fuca Plate beneath North America. This volcanic chain is around 40 million years old. They extend from Lassen Peak in northern California through Oregon and Washington and then for another 125 miles north of Vancouver, British Columbia. (Yes, there are many volcanoes in British Columbia!) Subduction still occurs off the coast parallel to the Cascades chain, and as long as it continues, magma will be generated beneath the North American Plate and volcanoes will erupt in the Cascades.
Click here to see an animation about subduction and some more explanation. There is a great YouTube video showing the subduction of the Farallon Plate, the migration of subduction northward, and the end of subduction in California. The author, Dr. Tanya Atwater, is a pioneer is this geology.

Dr. Rock


The Cascade subduction zone. The thicker continental plate overrides the

ocean plate. The colored dots represent earthquakes. Volcanoes can grow once

the subducted ocean lithosphere (rocky crust plus strong upper mantle) have

descended far enough into the soft asthenosphere (weaker mantle).

Two volcanoes: why do they look so different?

Dear Dr. Rock,
When I drove US 97 in the Bend, Oregon area, I saw two kinds of volcanoes. One kind, The Sisters, were high, steep and snowy. The others, like Lava Butte just south of town, or Pilot Butte, right in town, are low heaps of loose rock fragments. You can drive right to the top. Why do these volcanoes look so different?  --Bill Shaffer, Fresno, California

Dear Bill,
Volcanoes form where magma reaches the surface. Magma is a red hot mix of molten rock, gases and solid mineral crystals. Magma that erupts at the surface is ‘lava’. There are several types of volcano structures, and there shape depends on the runniness, or viscosity, of the lava they erupt.

The Sisters are stratovolcanoes (sometimes called ‘composite volcanoes). So are the other big volcanoes in the Cascades: Hood, Rainier, Baker, etc. These are made of successive layers of lava that has erupted tens or hundreds of times over thousands of years from the crater at the top of stratovolcanoes. The magma that erupts at these volcanoes is thick and pasty when it erupts, and is called ‘andesite’. Because it is so pasty, andesite lava doesn’t flow for more than a couple of miles, and usually a lot less than that. It piles up near the crater to make a high cone. The smaller cones you saw are called ‘cinder cones’ after the slag-like, sharp edged black lava fragments they erupt. (These are also called ‘scoria’). This magma is particular-well charged with gas, so that lava is blown upward into the air as glowing hot blobs of molten rock. These ‘cinders’ rain down around the volcano’s vent to built a mound of loose fragments.

Cinder cones might also erupt basalt lava, which is much thinner and runnier than andesite, so these lava flows might flow quite a way. Lava Butte lava flows spread outward from the cinder cone for over 6 miles. Cinder cones are a flash-in-the-pan—they usually only erupt for a few years and then their magma supply is exhausted. Here is a US Geological Survey website where you can learn more about the different types of volcanoes: http://pubs.usgs.gov/gip/volc/types.html .

This sketch shows a cross section through a cinder cone. It is a heap of loose fragments- no lava flows are found in the upper cone. Image by USGS.

The Middle and South Sisters from the summit of the South Sister. These are stratovolcanoes.

Mount Baker (10,781') in the north Cascades of Washington. Erosion has revealed the layers of lava that built this active stratovolcano.

Lava Butte, south of Bend Oregon, is a classic cinder cone, made of a heap of scoria and with a small crater on top. Note the lava flow in the foreground. Photo by USGS.