Pacific Northwest NAGT #3 Diamond Craters

The Pacific Northwest NAGT meeting was supposed to have 4 days of field trips, and one day (Saturday) of meetings. This years meeting only had about a 1/2 day of meetings so Saturday afternoon we headed out to Diamond Craters,, BLM designated "Outstanding Natural Area". Diamond craters began erupting about 20 ka and according to the the Global Volcanism Program website was last active about 7 ka. But according to our guide, there may be indications of eruptive activity in archeological sites that are less than 500 years old. 

  

From the ORE BIN vol 26 No 2, Feb 1964 

Unfortunately time was limited so we were only able to make three stops in the area, but each stop represented a different kind of volcanism so it was a great overview of the eruptive history: The first stop was a pair of Maars at the western end of the road. The first was smaller and dry, but the second (Malheur Maar) was deep with an active mosquito breeding farm at the bottom.

Maars/craters are generally caused by the ejection of hot steam and other volcanic gasses. The pressure of these gasses blow a hole in the surface that becomes the crater, but the eruption containes little to know magmatic material. So at our second stop we saw an eruptive area that showed indications of fountaines of eruptive matieral. Red Crater was a lapilli crater built up to about a hundred feet on the eastern side. The rim was comprised of lapilli sized tephra that had fused while still molten. Scattered around the site were a number of "Breadcrust Bombs". Volcanic Bombs that were beginning to cool and harden on the outside while still molten and outgassing on the inside. The release of the internal gasses cause the bombs to continue to expand, stretching the outercrust creating cracks like a crust of baked bread. This bomb was found about 50 feet from the crater rim.

Our last stop was Lava Pit Craters. Actually three craters formed by drained Lava lakes. Eminating from each lake are a sereies of tubes and caves of highly basaltic lava. 

One of the pits has a large cave/tube with lavacicles hanging down and a hornito on top.

 

 

Unfortunately because our time was limited, we did not make the hike into the central vent area with more than 30 vents and some "dribblet spires" where smalll amounts of molten lava is forced to the surface with just enough energy to run down the sides as it cools. Sort of like the magma version of a drip sand castle.  Oh well, it gives me a reason to make the drive back. 

Pacific Northwest NAGT Field Trip #2

I began writing about the 2011 Pacific Northwest NAGT field meeting here. On Friday we circumnavigated Steens Mountain. The final stop was in Colony Canyon south of Fields, Oregon near the Oregon Nevada Boarder. The area was postulated to be accreted terrain that was originally near the continental craton, but has been moved hundereds of kilometers east by the extension of the Basin and Range Province. There were numerous outcrops of highly metamorphic rock, and not enough time to thoroughly explore.

Andy and Turk debate the Metamorphic grade of the outcrop

I am not strong on metamorphic rocks, but I know a nicely folded schist when I see one, and it makes a nice folded structure for a Friday.

The schist was actually folded by three separate events, the first forming the shist planes, the second altering the foliated planes into wavey folds, and finally a large tilting of the whole block to dip towards the north east. The layer on the right that appears to be intruding into the schist was interpreted by Turk and Andy to be Ultra-mylonite. The area was also full of granitic intrusions with lots of trace minerals, many of which I could not identify.



A great stop, but it would take a field season to really get a feel for all of the geology.

Pacific Northwest NAGT

So last weekend I went to my first Pacific Northwest NAGT meeting. The meeting is a collection of mostly 2-year geology teachers who spend 4 days travelling around the area and one day of actual meetings.  Because this years meeting was located at Malheur Field Station in Southeastern Oregon, the first day of the meeting was spent getting there. As many of the participants (and the meeting host) were from the coast area they started near Salem and had a field trip driving to MF, while I took the more direct routes south on 395.

MFS is located northwest of the Steens Mountains on the border between the Basin and Range and the high volcanic plateau of Central Oregon. Although the Steens are an archtypical fault block mountain range, most of the features of the trip focused on Volcanic and Thermal features of the area. The Google map screen shot below shows some of the features we stopped to look at, with red balloons the stops that I will post about in this and the next couple of posts.

One of the first stops on Thursday served a dual purpose. The cap rocks shown below are Devine Canyon Tuff, and there is normal faulting down slope (north) that identifies the Brothers Fault. The Brothers fault at the surface is normal faults, but in general it is a strike slip fault that is the boundary between the relatively stationary Lava High Plains, and the (westward) extension of the Basin and Range to the south.

At this stop there was also a road cut through the tuff which afforded an up close look of the Devine Canyon Tuff. The Devine Canyon Tuff is one of four large welded tuffs in the area: The Rattlesnake (~7.02 Ma), Prater Creek (8.5 Ma), Devine Canyon Tuff (~9.7 Ma), and Dinner Creek (~15.5 Ma). The Devine Canyon Tuff eruptive center was ~20 miles northeast of MFS (~15 miles SE of Burns, OR) covered an area of 18,600 km2 (195,000 k3)to a fairly uniform thickness of about 30m. Because of its size, the Devine Canyon Tuff (and the Rattlesnake Tuff) is a good geologic markers throughout SE Oregon.

On Thursday we also drove north of Burns to look at the Rattlesnake welded Tuff (235,000 km3 with an eruptive center (~50 miles NW of MFS), and where the Dinner Creek Welded Tuff contacted the Mesozoic aged accreted terrain that makes up of much of Oregon (but is mostly covered by Tertiary Volcanics) 

On Friday we set out for a ~250 mile circumnavigation of the Steens Mountains. The east face of the Steens is steep exposures of Steens Basalt, and older layers. This vantage point is from the NE looking down Pleistocene Lake Bed at the base of the Range

Further along, we stopped at Mickey Hot Springs, a series of thermal pools that are being investigated for their potential to produce commerciall scaled geothermal energy. There were a series of hotsprings and abandoned vents in the area. The stricking thing to me though was the overall lack of thermal deposition. There was some sinter, and some algal mats that had lithified, but the area was very low in carbonate deposites that are often associated with thermal areas; in fact the water at the hot springs is fairly low in any dissolved ion content, which is part of what makes it attractive as a geothermal resource. Lastly, because the source of the hot water is not magma (it is hypothesized to be fault driven) so the thermal area had almost no SO2 and the associated sulfur smell. All in all it was a pleasant place to lunch.