Geologic work at Jordan Craters
Updated: May 21, 2020
This content originates from the BLM Oregon and Washington Facebook site.
Reproduced with permission.
As far as Oregon geology goes, a few thousand years ago is recent history. That’s what makes Jordan Craters in southeast Oregon so impressive – 27 square miles of volcanic rock that looks like “the lava just stopped flowing yesterday,” said Sammy Castonguay, a geologist with Friends of the Owyhee. “It’s that fresh.”
The lava flow at Jordan Craters is almost exactly halfway between the Alvord Desert and Boise, Idaho. It is significant in size, big enough to be seen from space, but a fraction of the lava flow size at Craters of the Moon National Monument in Idaho. BLM geologist Andrea Bowen, who has been to Jordan Craters 15 to 20 times, said since the basalt lava is pristine and not eroded, it’s easy to see the original texture and how it flowed through tubes.
“The lava flows, when it ejects out of the vent, the top solidifies, because it gets cooled by the atmosphere, then the molten part gets insulated, so it kind of develops these tubes,” explained Bowen.
The mobile and volatile molten rock at Jordan Craters created good examples of pahoehoe, a Hawaiian term used to describe smooth or ropy lava flow structures. Perhaps the most perplexing thing about Jordan Craters is that nobody knows when the lava first flowed, or how many times it flowed after that, due to “super inconclusive” dates, according to Bowen. Geologists do know that most the lava likely flowed from one main vent, called Coffeepot Crater, in a southeasterly direction until hitting an ancient stream and creating what is now called the Cow Lakes.
In the 1980s a charred twig from the lakes, presumably where the lava damned the water basin, was dated as 3,200 years old. A study the decade before estimated the lava flow as 4,000 to 9,000 years old, based on lichen growth rates on the volcanic rock. But the lava itself has never been dated, something Bowen and Castonguay intend to do as early as this summer with field schools. The field schools will use a dating technique called cosmogenic helium dating, which essentially estimates how long rocks on Earth have been exposed to the sun.
“There’s a lot of stuff that still should be answered by small projects like these,” said Castonguay, who noted the research will involve local students but also labs at the California Institute of Technology and the University of Wisconsin-Eau Claire.
The BLM is also interested in projects that officially map the locations of caves and Native American heritage sites, said Bowen. The rock at Jordan Craters may be young compared to other locations, like the more than 400 million-year-old rock in the Cascade-Siskiyou National Monument in southwest Oregon, but it still warranted BLM protection as an area of critical environmental concern, and the reason is obvious.
“I think it’s one of the more easy-to-interpret geologic features,” said Castonguay. “This is one of those that really doesn’t take a large imagination to point and say – that was a lava flow.”
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