Armchair Geology - Bonus Notes from the first fieldtrip!

By Keith Douville, Geology Class Student and Scholarship Volunteer

On September 22, we had our first field trip of the class, focusing on the lower parts of the valley.  Due to smoke from the Okanogan complex fires, we decided to focus our trip on the Twisp River valley.  We began with older rocks and as we moved up the valley, we moved up in time as well. 

Newby rocks at the junction of Poorman Creek are discussed

Our first stop was at the junction of Poorman Creek, at an outcropping of rock.  The rocks observed here were of the Newby formation, the earliest rocks we could observe as the Hozameen formations are typically only visible further to the west.  Newby rocks are a combination of igneous and sedimentary rocks, formed from island arcs and their surrounding oceanic areas.  Because they were located near a fault zone, they were squeezed and often metamorphosed.   The green color of these rocks is an indication of this metamorphic activity, and can hide the original volcanic texture.  Quartz veins in these rocks were later added as an intrusion after pressure was released and liquid rock flowed into the cracks.  These breccias were more pyroclastic than basalts, evidenced by the larger angular pieces surrounded by sediments.  Other formations near this area include intrusions (and associated mines) such as the Alder Creek and Spokane grade areas.

Our next stop was at our instructor Eric Bard’s house.  Here we examined sediments that were laid down around the volcanic islands.  These sedimentary rocks are known as argillites, or more commonly as shale.  Because of the enormous amount of activity following deposition in this dynamic geologic landscape, these shales were “cooked” and became argillite.  This “cooking” process has destroyed many but not all of the fossils that you would expect to find in sedimentary rocks.  Despite that fact that these rocks formed all around volcanic islands, some of the parent rocks that the sediments originated from are not volcanic in origin but may have travelled longer distances and were laid here by ocean current movement.   The rocks here differ from the Newby formation with smaller crystals and finer sediments.  This argillite can be a challenge for current valley residents because of its inability to hold water and makes a challenge when drilling wells when compared to drilling in glacial tills. 

Outcrop of high energy conglomerate along the Twisp River

Our third stop, moving up valley ahead in time again, was at an outcrop on the side of the road.  These rocks were a high energy conglomerate formed from alluvial fans extending beneath the ocean surface.  Adding to these fans of sediment from the mainland were again oceanic deposits that may have travelled great distances.  The larger fragments in these rocks are more rounded, indicating the energy of moving water that smoothed them before they were buried and eventually became rock.  The shales around the edges of these rocks show the less energetic environment expected of deeper ocean environments that surrounded these fans.

Low grade coal seams along the Twisp River are described

Moving again forward in time, we stopped at a low-grade coal seam a bit further up valley.  Like all coal, this rock was formed from organic compressed swamp material.   The layering at this site may indicate different climates as the sediments were laid down.  The weathering at this site is impressive showing chemical reactions which can change the colors of rocks, some to red.  This red color is not common with rocks until exposure to the air, and then it often indicated iron in the rocks as they “rust”.  The coal here is not of high quality and later attempts to burn it with a torch by a classmate were unsuccessful, so I cannot recommend shoveling a truckload to heat your home through the long Methow winter!  It is still impressive to see such a variety of geology in the area however, and to imagine the swamp that once was at this site. 

When I originally thought of geology in the Pacific Northwest, I thought of volcanoes and great eruptions.  Our next stop showed us a bit of evidence of that.  We stopped at a cut bank along the river to look at Mazama ash, which was deposited from the great eruption of Mt Mazama which collapsed to form Crater Lake in Oregon.  This was a relatively recent event, and the ash can be found throughout the Pacific Northwest.  Look for the bands of white, extremely fine grained, slippery to the touch ash in cut banks as you travel about.

Next, we looked at some Midnight Peak volcanic formations. These newer rocks formed from the subduction of Cascade episode lavas, although we don't know exactly where all of the volcanic centers for these flows were. These rocks formed at the same time as the Oval Peak batholith, but instead of slow cooling underground as occurred in that batholith, the liquid rock flowed to the surface as lava and cooled faster. White crystals in the rock show slower underground cooling; after eruption the surrounding rock cooled faster. 

(Photo:  Midnight Peak formation volcanics.  Note the difficulty of viewing the rock through weathering and lichens.  To ID your rocks more effectively, try to crack it open with hammer (use safety glasses).)

Twisp Valley schist at War Creek

Our final stop of the trip was at War Creek.  The creek had a mass wasting or washout event in 2011, exposing the Twisp valley schist beneath.  While stream blowouts such as this can be a pain for road and trail users attempting to access the backcountry, they can be a blessing for geologists by removing the pesky overburden, in this case 13,000 years of soil covering the rock below. The rocks here have distinct linear foliations from metamorphic activity.  As pressure was placed on the rock from a consistent direction, the particles in the rock aligned themselves perpendicular to that pressure and formed the foliations. To see this process yourself, try mixing mica flakes in play-doh and then squeezing a ball of it between your palms.  Break the flattened ball in half and see how the flakes have aligned perpendicular to the pressure. Veins in this rock often contain quartz intrusions amid the sedimentary and oceanic parent rocks which have been metamorphed. 

An intrusion of quartz within the War Creek schist

This field trip was great with many interesting questions from the class.  The areas we travelled to and the rocks observed raised questions about the Earth, plate tectonics and the crust, the formation of planets and cosmology, the formation of minerals, and some of our unique minerals such as Oakanogenite.  We were left with an excitement for our next field trip, which occurred further up the valley. 

Geology of the Pacific Northwest with Instructor Eric Bard - Notes from the thrid class

By Keith Douville, Geology Class Student and Scholarship Volunteer

On September 24 we had our third class meeting of Geology of the Pacific Northwest at the Methow Valley interpretive center to discuss the Cascade Episode, which covered the early establishment of the roots of the Cascade Mountains that occurred to the west of the Methow Valley, and the great basalt flows to the Southeast. 

The Cascades in Winter.  Photo by John Scurlock

The Cascade Episode begins at the end of the Challis Episode and still exists today.  It is important to note right away that the uplifting and rise of the modern Cascade Mountains (and the Olympics which remained a shallow marine coast) did not occur until about 5-7 million years ago, and that for much of the Cascade Episode only slight elevation rise was occurring.  The Cascade Episode is marked by a northward subduction of the Kula plate, causing its eventual breakup and the installation of the Farallon or Juan de Fuca plate on the coast of North America, roughly about where the I-5 corridor lies today.  The Farallon plate was originally further south, near California, but moved northward and began a shallow subduction under the North American Plate.  This subduction of the Farallon plate produced the magmas of the Cascade arc. 

For long periods of time (36 million years), this magmatism along an Andes-type margin produced volcanic centers up and down the Pacific coast.  Here in the North Cascades, greater uplift has allowed much of the volcanic rocks to erode away leaving only the plutonic roots (such as Dome Peak and parts of the Pickets).  Further to the south, generally south of Snoqualmie Pass (such as in the Ellensburg formation, the Ohanapecosh, and Stevens Ridge) many of these volcanic rocks remain in place at the surface and cover earlier material.   In the Ohanapecosh, andesites, rhyolites, and ash/mudflow material is nearly 10,000 ft thick in places and hides evidence of earlier rocks effectively from view.  Not all of the early volcanic centers are known, but some ancient calderas identified include Fife’s Peak which shows an explosive history of volcanism.

 

Mount St. Helens

Today we have many stratovolcanoes in the Cascades such as Rainer, Adams, Baker, and Glacier Peak.   These large and steep volcanoes have magma filled chambers and can spew ash, pyroclastic flows, and lava.  These differ from calderas left behind because calderas are the collapsed remains after magma chambers have been expended and can cover even larger areas.  Some volcanoes are more gentle sloped and have lava which flows more easily, with less explosive power, and are known as shield volcanoes.  Many of our volcanoes are active, others are dormant, and few are dead.  These volcanoes provide beauty and can provide rich soils, but are also hazardous to live near, especially when covered in glaciers which can liquefy into lahars during eruption events.  Ashfall and earthquakes are a more likely hazard here in the Methow today.  Monitoring of seismic activity helps us manage this risk today and hopefully we will not experience major eruptions in our lifetime. 

Magmas evolve and this evolution can be seen in the rocks produces at different times in the life of a volcano as well.  Early on, basalts and andesites are found from activity.  Later, silicas found in rock indicate a more explosive nature from the disgorging of more root rocks.  Less mafic mineral gradually become present and we begin to see more dacites and rhyolites.  The Methow volcanoes show high silica content and andesites, indicating an explosive past.  The silica rich felsic rocks are formed from a tight network of bonds under high pressure. 

Despite the large amount of volcanism in the Cascade episode, it pales in comparison to earlier ones.  Essentially it has been a chain of volcanoes up and down the coast, occasionally rising above the coastal plain.  Volcanic intrusions primarily are located at fault zones.  Magmatic activity seems to be correlated with a steepening of the subduction zone.  Uplift only recently changed the landscape 5-7 million years ago, giving birth to the rain shadow effects that we see today.  The uplifting that occurred also created a “fold” with the Olympic Mountains to the west, the Puget Trough forming the low spot, and The Cascades to the east.  This folding that occurred relatively recently is probably caused by resistance to the western movement of the North American plate at the subduction zone, and this explains the uplifting. 

Basalt columns and terraces near Dry Falls.

The great basalt floods for which Eastern Washington is known also occurs during this period.  The Columbia River basalts in Washington and Oregon and the Chilcotin Plateau basalts of British Columbia are over 5000 feet thick in places and cover nearly all of the older geology with some 200,000 km3 of material.  Immense amounts of lava flowed through hundreds of dikes and spread out over the landscape all the way to the ocean.  This occurred many times, and the area originally covered is probably even more extensive than we realize due to erosion and uplifting of the Cascades, which occurred later.  Lava basalt flows such as these are usually seen at spreading centers between plates, or at hot spots where a mantle plume of magma extends through the crust.  The Yellowstone hot spot has left its mark across the North American plate as it moved to the west, and the timing seems right to attribute the Columbia basalt floods to it.  It also seems the North American plate covered a spreading center in California, and the consequent Nevada-Oregon rift zone lies in line with the Chief Joseph dike swarms where much of the lava appears to have originated.  So while still debated, the hot spot combined with a rifting zone provided the conditions for these floods.  The Ginkgo Petrified Forest near Vantage, WA contains logs that were once buried in mud and encased in the lava flows.  The species there tell of a time before the Cascades were uplifted, a time when arid conditions did not prevail.  

The Cascade episode is one I find very interesting due to its more recent activity than the other earlier episodes.  The basalt floods that are visible as you travel Eastern Washington are intriguing to me, and are indicative of what I thought of when I thought of the Cascades originally-lava, and lots of it.  I also like the idea of living among some of the youngest mountains in the world, only recently uplifted.  Makes you want to keep studying geology so you can keep unlocking mysteries, doesn’t it?

On Behalf of the Birds

A rufous hummingbird, photo taken by Mary Kiesau

Like a good gardener chronicling successes and failures in the garden, I diligently keep a list of my concerns and observations of our property and all of the related chores I wish I might get to in the spring and summer to come.  This list is often inspired as much by rational thought as panic, when I witness the march of weeds throughout my neighborhood and property:  call the County to order beneficial insects, mow whitetop, pull cheat and bulbous bluegrass in May, pull Barnaby in the heat of July, (ugh) an outbreak of Russian thistle to pull in August.  Then the shortening days of September give me an out to my semi-successful campaign, nothing more I can do about the weeds it seems. 

One priority item on my list that was truly successful this year, surprising me I have to say, is preventing the window kills of songbirds at our house.  For 9 years we lived in yurts on our property, with vinyl windows and wooden slats ensuring that even the most careless bird would not be drawn in.

The first spring we built our house changed all of that; songbirds, particularly in May and June, met their death on our windows with such regularity that my daughter Sally and I tried putting up stickers, hanging reflective tape, keeping the shades drawn, providing safe haven to stunned birds hoping they would revive.  We listened with dread when the smack on the windows would sound.  Was it a bad one?  We knew based upon how loud the smack.  In spite of our efforts, none of these measures seemed to help.

Okay, we thought, let’s move the birdfeeder, it must be too close to the house.  This proved to be disastrous!  Now with the feeder 100 feet from the house, the birds had just enough opportunity to gather speed and hit our windows with this greater velocity.  Moving the feeder was not the silver bullet we had hoped for. 

Could taking down the feeder altogether help to solve this?  We tried it, taking down the feeder that provides us with so much awe and enjoyment… and lo and behold, this spring and summer, we reduced our bird strike deaths to just a few.  And though I really do miss seeing the birds out our windows with greater regularity, I am greatly relieved to have found a solution on my property that makes a positive impact on birds and their survival in the Methow.

My to do list for next year?  Pulling and mowing weeds of course, keeping the bird feeder down to test my theory for another season, and taking hikes with Sally, our binoculars and bird book, to enjoy and identify the fabulous songbirds in the Valley. 

When she's not caring for her beautiful property and all of its wildlife, Jeanne White serves as the Methow Conservancy's Land Project Manager, helping conservation easements come to life!