The Blue Planet: Geology and the Pacific Northwest

Notes from the 2nd class of the Big Ecology Conservation Course by Course Volunteer Bob Herbert
The second night of the Conservancy’s Big Ecology course was a fascinating presentation by Alan Gillespie that revealed the dynamic geology of earth.  Like all disciplines in science these days, geologists continue to revise and hone their understanding of how the planet came into being, and how it has changed over time.

            

Basalt in the Columbia River

We learned that rocks are divided up into three categories: igneous, sedimentary and metamorphic.  Igneous rocks are created through the recycling action of volcanoes.  Granite and basalt are both examples of igneous rock.  As tectonic plates collide, the heavier one will dive under the lighter.  As the rock gets forced downward into the mantle of the earth it melts the leading edge of the plate and through a volcanic eruption, it reappears on the surface as lava.  

             

Sedimentary rocks are created through a layering process.  For example, layers of sand build up through wind and rain erosion and with time and pressure they form sandstone.  When sandstone is exposed to the elements it erodes into beautiful and delicate hoodoos and arches, and Utah and Arizona are filled with amazing examples of these.

             

Metamorphic rocks are formed under intense heat and pressure.  Some of the rock crystallizes, while other parts become warped.  When these rocks are exposed, they show banding that is curved and distorted, instead of linear. 

             

We discovered that geology is no different from other disciplines of science in that its origins were found in stories and legends.  These legends served as factual science for the people of that time period and geographic location.  The legends transformed over millenniums, and now they are nothing more than humorous stories about our ancestor’s lack of scientific knowledge, but for a long time this was how science was taught.  One of the main things that these stories provided was a process for how things worked.  It didn’t necessarily have to be correct to sufficiently explain a natural process that people wondered about, like the sun rising and setting every day.  Science is the modern outcome of these campfire stories, and science continues to improve and adjust its understanding of the world we live in.

            

The discovery of radiometric dating opened the door for geology.  This process measures the amount of Carbon 14 found in a rock and through a mathematic equation, the age of the rock is determined.  This discovery allowed geologists to measure the ages of various layers of rocks and fossils and through this data our modern understanding of earth’s geology and plate tectonics was born.  Carbon dating has confirmed that the earth is 4.55 billion years old.

            

The Earth is made of a "core," "mantle," and "crust"

When the earth was originally forming, the heaviest elements sank to the center, which is how our super-heated iron core came into being.  Uranium is found in the transition into the outer core and mantle, and the earth’s crust formed as the surface of the liquid mantle cooled.  Scientists believe that our moon was actually a large meteor passing through our solar system and it slammed into the side of earth.  A portion of earth broke off and the remnants of this collision went into orbit around the planet, giving us our moon.  At the same time, the collision tilted earth’s rotational axis.  It is this tilt that provides the four seasons for our planet.  If earth’s orbit around the sun was perpendicular instead of being tilted at 23.44 degrees, then the weather at your home would remain the same year round.       

             

The rotational velocity of earth (approximately 1,000 mph) combines with the electrical field that surrounds the inner core, and together they create the dynamo that produces the dipolar magnetic field which protects earth from cosmic radiation.  This phenomenon not only provides earth with protection from solar radiation, but it also provides us with magnetic north/south for navigational purposes.  The Van Allen belts are the name of this magnetic field and they are also responsible for the northern lights.              

             

By studying fossil records geologists have confirmed two major extinction periods that occurred 250 million years ago and 65 million years ago.  The oldest is named “Snowball Earth” and it was a massive ice age that covered the entire planet with snow and ice.  As the glaciers receded toward the poles the age of the dinosaurs slowly began.  Giant reptiles dominated the surface, air and oceans until 65 million years ago.  At that point, a meteor is thought to have hit the earth and the dust from the impact blocked out the sun long enough to drive the dinosaurs into extinction.  We are currently living in another period of mass extinction (right now nearly 20,000 species of animals and plants around the globe are considered at high risks for extinction), and unfortunately, humanity seems to be the cause for this one.

             

300 million years ago there was one supercontinent called Pangaea

Geology took another leap forward when it was determined that the continents were joined together about 300 million years ago in one supercontinent named Pangaea.  The crust floats on top of the liquid mantle, and over time it broke into pieces. Over millions of years they drifted apart from each other and created the continents as we know them.  Geologists determined that oceanic plates are heavier and continental plates are lighter, and they are all in motion.  Fault lines have been created where these plates have come together, and when these giant chunks of earth slip against each other they create earthquakes.

             

Even though North America and Asia appear to be seamless pieces of land, they have actually been created through a series of smaller pieces slamming into the larger, main piece.  India is a perfect example of a smaller piece of land crashing into a larger one.  The point of contact for India was in the north and the collision with Asia created the Himalayas.  We also learned that the west coast of North America was not part of the original craton (an old part of the continent), which broke off from Pangaea.  The Rocky Mountains were created when a piece of land drifting east across the Pacific Ocean slammed into the older bit of continent.  The Pacific Crest is another example of how a collision between two plates produced a north/south oriented mountain range in North America.

Another geological discovery that helped explain earth’s ever-changing landscape was hot spots.  The Hawaiian Islands are the most obvious example of this.  Kauai was the first island to form, but as the crust shifted over the hot spot in the mantle, another neighboring island formed, and so on.  This is why the only island with an active volcano is the Big Island, because it is the last island to be created, and it currently sits on top of the hot spot.  We learned that Washington was also over a hot spot at one point in its history.  The basalt created in the Columbia River Basin was from the same hot spot that is now underneath Yellowstone National Park.  The amount of volcanic material (basalt) deposited in Washington from the hot spot was approximately 80,000 times that of the eruption of Mt. St. Helens, and that same plume of heat now drives the geysers and hot springs of Yellowstone.

             

Once all of the big pieces of the west coast were in place, then a combination of volcanic activity and glacial erosion created what we now know as the Methow Valley.  Mt Robinson is actually one of the dividing lines between continental rock and basalt (volcanic) rock.  A quick glimpse on Google Earth confirms the rock to the west of the peak is charcoal grey eroding basalt and the rock to the east is lighter and granite in appearance. 

The upper Methow is U-shaped because it was carved out by glaciers.

The upper valley (Mazama & Lost River) was formed as a result of a glacier 7,000 feet thick that covered the North Cascades, and it began receding 17,000 years ago.  The shape of the upper valley in the Methow is “U” shaped which is indicative of glacial erosion.  Below Carlton, however, the erosion becomes “V” shaped, which indicates erosion from water runoff alone, so the Methow was actually formed by two different geological actions.

The northwest is rich in volcanic nutrients and boasts enormous biodiversity.  The Cascade Range is a wonderful combination of plate tectonics and volcanoes, glaciers, forests and rivers, and thanks to Alan ’s expertise, we all have a better understanding of how the magical Methow came into being.

Geology of the Pacific Northwest - Notes from the fourth and final class

By Keith Douville, Geology Class Student and Scholarship Volunteer

Our final class of the Geology of the Pacific Northwest class was on October 1, 2012.  The first thing we discussed was a bit of review, to reiterate some of the concepts that we went over earlier.  Questions on the Kootenay, the Omenica arcs, orogeny episodes, The Coast range episode, the breakup of the Kula plate, the timing of the Cascade episode, and the differences in the formations north and south of Snoqualmie pass were rewarded with chocolate. 

John Nickel from the class had found a fossil at our second field trip, and George Wooten had written a small interpretive piece on it.  The fossil is on display at the Methow Valley Interpretive center. 

Some questions from the class were discussed and we talked about challenges of geology in general.  Often geologists are forced to interpret a landscape with very little of the original material intact, say 10% or so.  This material has been faulted, broken, and accreted.  Follow this with multiple glaciations events and subsequent flooding.  Finally, our ability to replicate these processes is limited at best.  These challenges make interpretations difficult, but it is the challenge which can make it so rewarding as well. 

Following the review and questions, we discussed the Ice Ages and what they meant to the area.   These events over the last 5 million years have had a profound impact on the landscape, sculpting it into the landforms which we see today.  While we are still in the Cascade Episode, the last 5 million years have been most instrumental in changing the shape and function of our landscape and are worth additional scrutiny. 

We are still in this recent Ice Age by most accounts.  The ice ages have been found to correlate with the Milankovitch cycles, which describe the changes to the Earth’s climate from the regular changes in the tilt and orbit of the Earth.  Other theories to the induction of the current ice age are the India plate collision which gave rise to the Himalayas, in turn changing the amounts of atmospheric dust, ocean circulation, and atmospheric CO₂ removal as rock weathering increased the amount of calcium carbonate in the oceans.  The PBS series NOVA produced “Cracking the Ice Age” which can help describe some of these changes.  The advent of the ice ages allowed for an increase in two types of glaciations: Alpine and Continental. 

A classic glacier-carved U-shaped valley in Mazama.

Alpine glaciation has had a significant impact on the Methow and the Pacific Northwest.  Several landforms are commonly seen from the movement of alpine glaciers in the area and were discussed in class.  Cirques are bowl-shaped depressions formed at the head of glaciers as the weight of increasing ice carves out the side of a mountain.  These bowls often contain a mountain lake after the ice melts.  A Kame forms when debris, usually rounded outwash, forms laterally along a retreating glacier and a terrace is left behind.  Examples of Kame terraces are found near Sun Mountain, Pug flat, and Rooster flat.  Distinct U-shaped valleys are formed as a large alpine glacier scours a valley.  This is different than the V-shaped valleys that form with stream erosion.  The Methow valley’s wide U-shape with steep walls and a wide flat bottom is a classic example of this type of alpine glacier erosion.   Lake Chelan is an example of a fjord lake that has formed from another U-shaped valley or glacial trough.  A Nunatak is exposed rock that protrudes above the surrounding ice, and many of the horns that are present in the North Cascades are pinnacles of rock that stayed above the ice.  Erratics are rocks that are carried by glacial ice and then deposited as ice retreats, or moved by glacial floodwaters, and can be seen throughout the valley floors.  Erratics are often composed of different rock than the surrounding area and are easily spotted.  

The Stauning Alper Glacier of East Greenland is a classic alpine glacier with the main ice sheet separating peaks of granite from the heavily eroded valley.  This is probably what the Methow looked like 15,000 years ago!

 As glaciers melt and retreat the landscape is changed as well.  Outwash plains and lakes can deposit large amounts of silt, and this is common in valley floors.  These outwash plains typically have sorted material, with distinct layering or stratification.  This differs from glacial till, which is deposited in moraines usually at the ends or lateral edges of glaciers and is poorly sorted, with angular chunks surrounded by finer materials.  Drumlins can be found in the area as well, but usually in the lowlands and not in the mountains.  These mysterious features are elongated hills, oriented along the long axis with the direction of glacial travel and are thought to form within glaciers as till is repositioned and deposited.  Striations or scratches in bedrock can indicate the direction of ice travel as well. 

Continental glaciation occurred in Washington in addition to the alpine glaciers.  Continental glaciers are huge, one of the major differences from alpine glaciers, in the range of 50,000 sq. km or so.  The Frasier or Cordilleran ice sheet reached its maximum in the Methow about 15,000 years ago.  The Winthrow (yes, Winthrow, which is in the Waterville Plateau area of WA) moraine marks the terminal of one of its lobes.  As the ice retreated, sometimes large chunks of it remained in debris and as it melted kettle ponds were formed, such as Dead Horse Lake.  In Western Washington the Puget Lobe extended east of Olympia and the Juan de Fuca lobe extended further north between the Olympics and Vancouver Island.  

Withrow is a town in the Waterville Plateau (east of Chelan) where the terminal moraine of the last major glacier in the Columbia Plateau is found.  This moraine, from the Okanogan lobe of the Cordilleran Glacier, shows amazing features of past glaciation including kettle lakes, erratic boulders, drumlins, kames, and loess soil. A place to visit says instructor Eric Bard!

Fine silts forming from glacier erosion can be moved by self generated winds off the cold glaciers.  When wind deposited silt collects in dunes it is called loess, a major feature of the Palouse landscape in southeastern Washington.  Loess is known for its high moisture retention and nutrients, and makes for great farmland. 

Pipestone Canyon here in the Methow Valley

As huge amounts of water are generated from melting ice, coulees can be formed, such as Alta or Elbow coulee locally. Pipestone canyon is probably another coulee formed in the same way, from meltwaters or flooding as opposed to long lasting stream cuts forming deep flat bottomed canyons.  Sometimes these meltwaters would become impounded by ice and when these dams fail the results can be catastrophic.  J. Harlen Bretz won the Penrose medal, a prestigious award in geology, for his lifetime of research which led to the acceptance of the Missoula floods (aka the Ice Age Floods).  Lake terraces formed high on the hills around Missoula show huge, ancient water bodies, and the channeled scabland landscape in Eastern Washington shows how multiple flood events fought their way to the ocean following collapse of the dams.  Crescent Bar shows how water can drop huge deposits, and the Wallula Gap shows how stronger rock formations can create choke points for the waters.  Bruce Bjornstad with the Ice Age Floods Institute will speak about the Missoula Floods on November 25^th 2012 at the Methow Valley Interpretive Center. 

We concluded talking about other geologic phenomenon that is very recent, geologically speaking, and some open ended questions.  The Little Ice Age, from about 1500 to 1850, left a mark on the Methow with small moraines left from glacial retreat.  Every 300-600 years a subduction earthquake can be a possibility.  One near Chelan in 1872 was estimated to be about 6.8 and created landslides throughout the Cascades, with fissures opening and water geysers erupting for days.  Rain is a common occurrence in the mountains, especially on the Westside, and mass wasting events are common here with the ground slumping and sliding down slope.  We discussed the long term challenges of maintaining roads such as Highway 20 in a mountainous landscape.  As our glaciers continue to shrink, what will it mean for the Methow?  When will our next ice age arrive?  What will we call our next supercontinent? 

This class covered a fairly broad range of materials, and did so in few class periods.  Our instructor Eric Bard’s ability to synthesize and present material from introductory geology to specifics on the Pacific Northwest was second to none, and we were lucky to have the opportunity to have such a knowledgeable and personable expert right here in the valley!  Class participants in this Geology of the Pacific Northwest class emerged knowing a bit more about the landscape they call home.  We learned to think like geologists, and we are a little more excited about rocks than we were before.  We have become time travelers, by our ability to interpret rocks that are from the ancient past.  The Methow Conservancy set up this great course, and the Methow Valley Interpretive Center provided a wonderful place for us to meet for these 4 weeks.  Most of all I would like to acknowledge our instructor Eric Bard for teaching us these great skills!  A big thank you to all of these folks!  Happy rock hounding out there in the Methow!

For further info on the Methow area rocks, check out the Methow Block Field Guide at: http://www.nwgs.org/field_trip_guides/6.%20Methow%20Region.pdf

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?

Armchair Geology: Notes from Class 2 with Eric Bard

By Keith Douville, student in the class

Hello again, another blog following the Geology of the Pacific Northwest class.  Our class this week was focused on “Methow Mysteries, Rocks, Geologic Events, and Connections.”  This time around we worked to draw correlations from the big picture to our corner of Washington and narrow the focus to our observations locally.  Students brought in rocks from around the Valley to observe and discuss.  This homework assignment of finding rocks was designed to get us comfortable looking at rocks and excited about local finds.  It did just that, with many folks bringing in great specimens to share.    

We began with a few questions to keep us thinking about the big picture.  I will list the questions here and follow them up with answers at the end.  Take the quiz and see how you do!

1)     What is the difference between a Passive and Active Margin?

2)     What major ocean opened up to change the Pacific coast from a passive to an active margin?

3)     What specific activity creates volcanic arcs?

4)     When did the eastern boundary crescent basalts arrive in geologic time:  Permian, Cretaceous, or Eocene?  (Hint: the times are listed from oldest to newest). 

5)     What fault divides the Okanogan and the Methow, running roughly from pipestone through 8 mile creek?

All of our sciences have roots in geology, as it is the foundation on which all natural events occur.  There are many good resources out there for geology students, and basic textbooks are a good place to start.  You don’t need to spend a lot of money, as often these texts can be found cheaply second hand at thrift stores or online.  One we discussed is Geology of the Pacific Northwest, by Orr and Orr.  Another more casual read that was discussed between students was The Restless Northwest: A Geological Story, by Williams.  When purchasing books keep in mind that many changes have occurred to our understanding of geology in the last few decades, so try to find one that discusses plate tectonics as this is relatively recent in our understandings of the Earth. 

So what parts of science have contributed to this understanding of geology?  Petrology is the study of rocks and is obviously valuable.  The identification of isotopes and their decay can help us determine radiometric ages.  Strontium and Rubidium ratios have helped us to determine where the approximate coastline of the ancestral continent of North America existed before the accretion of younger terranes.   The identification of geologic structures such as faults along terrane boundaries, areas of deformation, or folding can help us decipher changes and the timing of changes that occurred in our area.  Fossils can help date rocks to certain times, as can radiometric dating.  The stratigraphy of rocks and their environments can help us understand the dates of events, as layers are deposited at different times.  Just remember that the “top” may have once been at the bottom and that entire layers can be flipped or folded.  Finally, uniformitarianism is an important concept in geology.  This means that what we see happening in our world today can lead us to conclusions about what happened in the past, as we can assume that many of the same processes occurred to create similar features.

Here in the Methow one of the major events that occurred was the fore arc basin.  The basin that occurred between island arcs allowed for deep deposits of sediment to form rocks.  This was later uplifted as the area was squeezed between accreting terranes.   

Chert

The oldest rocks in our area are typically oceanic rocks from the Hozameen terrane.  These rocks were once part of the ocean floor and date from the Paleozoic to Jurassic time.  These basalts are often metamorphed, identified by a green color.  Radiolarians rich in silicas in deep water often form layers of chert (microcrystalline quartz) within these rocks.  These cherts provide evidence for a western source from the Hozameen Terrane for some strata in the Methow Basin fill (eg. Virginia Ridge formation).  

Next, in our general stratigraphy, came the Newby or Twisp formations in the late Jurassic.  These argillites (or more informally shale and volcanic rocks are from early island arcs and the surrounding ocean rocks.  These can be metamorphed later into other rocks and they can be a challenge to identify at times.  Remember that green rocks often indicate this metamorphism.  The red seen on some of these rocks usually points to iron oxide (rusting) on the rock surfaces and to get a good look break them open with a hammer (use safety glasses).  Drawing their name from Newby Creek, these rocks have larger mineral formations speckled amid smaller particles.  The sharp angles in the fragments in some of the volcanic breccias may form at the base of lava flows or as mud flows and the fragments have not had time to round as do river stones.  Some of the more violent explosions formed tuffs, although the exact location of ancient eruptions in not clear.  We are talking about millions of years ago after all!  Many of these rocks can be sedimentary, with volcanic parentage.  They become cemented together with silicas, iron, and calcite.  They can contain fossils, so keep hunting out there, you may find a few.  In fact, dinosaur fossils have not been found in Washington to date, but it seems likely that if found they would be in sedimentary rocks in the Methow area.  Find one and you will be famous!

Conglomerates and shale on top of Virgina Ridge

Close-up of shale (and bitterroot) on Virginia Ridge

Following the Newby rocks are the Fore arc basin fills.  These sedimentary sandstones, conglomerates, and shales were deposited over time between other formations and are of marine and stream origins.  They occur from different time periods ranging around the Cretaceous.  Some examples of these are in Virginia Ridge and Winthrop sandstones, and the Buck Mountain and Paterson Lake areas.  Some are comprised of more fine materials and are known as siltstones.  Many of the parent materials are of volcanic origin but as currents can move particulate great distances in the ocean it can vary.  Some argillites can be present, and we often see conglomerates in this formation which differ from breccias as the larger pieces contained within are rounded.  Remember that the conglomerates have rounded aggregate and indicate high energy rocks (think stones tumbling in a stream) and breccias have sharp aggregate and are from deposits that have not transported far or been eroded by water.  Many of the rocks in these formations are formed in submarine fans and under ocean mudslides.  Unique index fossils can be found in these rocks as well, which help us date them and learn about ancient extinct life such as Ammonites.  

The Midnight Peak Coast range volcanoes deposited volcanic rocks on sedimentary rocks, shown in places such as Goat Wall.  These are volcanic andesites. 

The local Pipestone Formation, which are mainly conglomerates, not soapstone, are formed by erosion from Okanogan batholith rocks to the east and were later cut out by glacial melt water.  Plant fossils like the extinct Dawn redwood can be found in them.  They weathered into pipe shapes and thus the name of the formations.  Zircon crystals in sandstones formed in the cretaceous period about 70 million years ago, but the dating of these rocks could be just dating the older minerals which make them up.  Any way you date them, they are still the youngest sediment stone found within the Methow. 

Throughout time, intrusions of igneous rocks appear as granitic rocks, some from lava flows and explosive events and some as slower cooling subterranean magma pockets.  The material to form these rocks was born in subduction zones, and the magma contained in these plutons can help to “stitch together” geologic terranes.  During the Coast Range episode, many of these rocks built mountains.  Along the margins of these rocks precious or valuable metals can be extruded from host rocks and concentrate.  This can cause excitement for miners and not surprisingly many of the mines in the area are concentrated along intrusive margins.  For example, the Alder Creek mine was a source of zinc and copper.  Be sure to use extreme caution around mines because of unstable rocks, chemicals leeching, rotting timbers, and low oxygen levels within mines that can be difficult to detect until it is too late.  Some other examples of intrusives are Oval Peak tonalite, Fawn Peak diorite, and Monument/Golden Horn granites, all from varying time periods. 

Next week we will cover activity to the West of us, notably the “Cascade Episode.” Stay tuned!

Answers to Questions from Above

1)      A subduction zone at the margin is the usual event that creates an active margin.

2)     The opening of the Atlantic Ocean begins westward movement of the North American continent, creating the active margin on the Pacific west coast.

3)     Subduction creates volcanic arcs. 

4)     The Eocene marks the arrival of the Crescent Basalts, about 50-40 million years ago.

5)     The Pasayten fault separates the Okanogan from the Methow. 

Keith has spent his first summer working on the Beaver Project crew here in the Methow Valley and he's eager to learn all he can about this amazing place.