Tag: Oregon

Hike with a Geophysicist

Robert (Bob) Lillie at the summit of Marys Peak

Have you ever wanted to travel back in time to see what the Earth was like thousands or millions of years ago? Well, then this post is for you!

A hike on Marys Peak is like a window into Oregon’s geological past. Marys Peak’s rocks, viewpoints, and vegetation, all paint a picture of large-scale changes that occurred in Oregon millions of years ago, and continue to shape the landscape today.

Hiking with Robert (Bob) Lillie—a geophysicist with a knack for interpreting the Oregon landscape—is like having a tour guide along for the journey.

Armed with a simple model of Marys Peak, rock samples, and two books on Oregon Geology authored by Bob, he met me at the Day Use Area on Marys Peak to begin our hike.

View of Marys Peak from Beazell Memorial Forest’s south meadow.

The Hike

  • Trailhead: Summit Trailhead (Marys Peak Day Use Area)
  • Distance: 3.5+ miles (summit loop trail + meadowedge loop trail)
  • Elevation Gain: approx 700 feet
  • Notes: Northwest Forest Pass is required to park at the Marys Peak Day Use Area where you will find ample parking and pit toilets. There are many additional hiking options on Marys Peak of various length and difficulty.

Marys Peak Rocks

Holding up a labeled bicycle helmet as a model, Bob explained that Marys Peak was made up of several layers of different types of rock, each with unique properties. At the base was black volcanic rock called basalt, followed by thick layers of light colored sandstone and dark shale, and at the top an intrusive rock known as gabbro. This hard gabbro layer, Bob pointed out, is where we would be hiking today.

Bob’s bicycle helmet model of Marys Peak.

Cool Rocks

You may recall from middle school science, that igneous rocks form when lava or magma cools and solidifies.  However, due to differences in formation and chemistry, not all igneous rocks turn out the same. Bob pulled out some rock samples- gabbro and basalt- and began to explain their differences.

Dark-colored basalt is a low-silica igneous rock that forms from thin, fast-flowing lava (think Hawaiian volcanoes) that cools and hardens quickly— within a few hours to days. Gabbro is also dark-colored with the same low-silica chemical composition as basalt, but forms from magma that cools very slowly below ground, taking 10s to 1000s of years to cool and harden.

The long cooling time allows large crystals to form in gabbro rock. On the other hand, basalt has very fine crystals, making it a bit dull looking and less valuable. Thus, gabbro is used in masonry in Oregon, often as a granite alternative, while basalt is used to gravel roadways.

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

Putting the rock samples away, Bob and I followed the gravel road part of the summit loop trail upward from the parking lot. Eventually, we reached some gabbro outcroppings, with large crystals glimmering in the sunshine. 

Heading up the summit trail to the first set of gabbro outcroppings

Weathering Time 

Remember, gabbro forms below ground. According to Bob, two miles of sedimentary layers once covered the now exposed gabbro rock. Of course, that was millions of years ago. So what happened? Where did the sedimentary layers go?

The answer lies in one of the most underappreciated geological processes— weathering an erosion. Weathering is the breakdown of rock by contact with the atmosphere, hydrosphere, and biosphere. Basically, exposed rocks get worn down over time with a little help from the environment.  This weathered material can then be eroded (moved away by wind and water), uncovering more rock that lies below. Sedimentary rock weathers and erodes easily, while igneous rock such as gabbro is much harder. 

 “Look up,” Bob exclaimed, “imagine two miles of sedimentary rock pushing down from above you.” 

The slow action of weathering and erosion removed it all! What a load off!

Mini-Yosemite 

As we hiked along the gabbro rock gardens, Bob pointed to some rounded outcroppings of gabbro rock that reminded me of pillow basalt— a form of basalt that results from cooling in water. Though pillow basalt can be viewed on the road up to Marys Peak, it made no sense that we would find it here in the gabbro layer. Something else was going on! Bob explained that the answer lies in a process known as spheroidal exfoliation.

With the slow removal of the weight of two miles of sedimentary rock layers, the gabbro sill would have fractured and broke into cubed or rectangular blocks. Then, spheroidal weathering would have taken over—discriminately breaking down the gabbro blocks; wearing down corners more than edges, and edges more than faces; and eventually forming rounded spheres surrounded by concentric “shells” flaking off.  Once exposed, these layers may erode and “peel” away layer by layer—much like peeling away the layers of an onion.

Spheroidal exfoliation on a gabbro outcropping

Bob compared the rounded rocks on Marys Peak to the huge granite domes (such as Half-Dome) you can see in Yosemite National Park. The same basic mechanisms of exfoliation apply, just on a different scale. Thus, Bob dubbed Marys Peak a “mini-Yosemite” in honor of the striking resemblance.

Hard as a Rock

At about 500 feet above the rest, Marys Peak is the highest mountain in Oregon’s Coast Range. In part, Marys Peak stands out above the other mountains because it is hard-headed or, as Bob puts it—stubborn! Compared to the sedimentary rocks that once covered it, the gabbro on top of Marys Peak is very resistant to weathering and erosion. The stubborn gabbro thus acts as a sort of shield to the elements, allowing the peak to remain prominent.

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

Island in the Sky 

The fact that Marys Peak is “stubborn, has essentially allowed it to maintain its height and, in turn, a cold subalpine climate. Marys Peak, as Bob describes, is “an island in the sky.” 

With colder, harsher conditions than other coastal mountains, Marys Peak exists as a remnant of the past. Rather than the typical Coast Range Douglas-fir/hemlock forest, Marys Peak is a botanical anomaly, and a very beautiful one—it has even been designated a Scenic Botanical Special Interest Area.   

The meadows, rock gardens, and noble fir forests that make up the upper reaches of Marys Peak are unique to the Coast Range today, but once would have been typical of the region. Botanically speaking, Marys Peak is living in the last ice age that ended about 12,000 years ago. Many subalpine wildflower species are found here. During our hike through the rock garden, Bob and I took note of several: harsh Indian paintbrush, spreading phlox, Cascade desert parsley, and Cardwell’s penstemon, to name a few; and in the meadows- glacier lilies.  

A gabbro wildflower rock garden on Marys Peak

Marys Desert?!?

But subalpine flowers were not the only botanical anomaly of note on Marys Peak. As we hiked farther up the summit trail, past most of the rock gardens, Bob pointed out a slightly lower ridge to the left on the south flank of the mountain.  Here we found another remnant of the past—a veritable desert!  

Some 6,000 to 4,000 years ago, during a warm, dry period, species still found today in the eastern or southern parts of Oregon spread into parts of western Oregon.  Later, as the climate again shifted toward cooler and wetter, most of these—what are known as xeric species—retreated back.  But this outcropping- with it’s thin, rocky soil (thanks again to stubborn gabbro) and it’s harsh, drying winds- held onto its xeric species. The west-facing of this area is especially important because high winds coming from that direction blow away most of the heavy snow blanket that covers other areas near Marys Peak summit. 

I was unable to see or identify xeric species from where I stood, but prostate lupine (eastern Oregon species) and sulfur flowered buckwheat (southern Oregon species) are apparently two xeric species to keep an eye out for. 

Marys Desert—A xeric rock garden (desert ecosystem) on the west-facing slope of Marys Peak  

Story Beneath the Scenery

About ½ mile from the start of the trail, we reached the summit of Marys Peak. Ignoring the unsightly communication towers behind us, we looked out into the horizon. The views on Marys Peak are reason number two for visiting—come for the wildflowers, but make sure you stay for the viewpoints (and the geology)!  

From the summit, looking to the west, you can see the Pacific Ocean; and to the east the Cascade Volcanoes are prominently on display, with the Willamette Valley in the foreground. With such scenery, it is easy to get caught up in the simple beauty of Oregon.

It’s also the perfect opportunity to start thinking like a geophysicist—which, according to Bob, involves observing the landscape and visualizing what happened beneath Earth’s surface to cause it.  Much of geology happens slowly. We can’t watch changes occur, but we can use what we do see to develop inferences regarding the past. Like watching the final scene in a movie, it isn’t too difficult to deduce some of the earlier scenes if you are paying attention.  As Bob puts it- “there is a story beneath the scenery.”  

Views from the summit of Marys Peak

Moving Plates

The Earth is composed of about 12 hard tectonic plates that move around on a softer part of the mantle, called the asthenosphere. These plates grind past one another, and they grow and shrink as they move toward, under, and away from each other.  The motion is messy, resulting in cracking and folding, as well as earthquakes and even volcanic eruptions. These large-scale motions help explain much of Earth’s formations, including those visible from the top of Marys Peak. 

Born in the Ocean

Marys Peak did not start out as a peak. Rather, Marys Peak, and the Coast Range in general, started out as rocks and islands scattered about in the Pacific Ocean. What is now Oregon did not exist 200 million years ago! Over long periods of geological time, the North American plate bulldozed these rocks and islands off the ocean floor, and in the process built Oregon.  

As Bob explained, Oregon sits along a convergent plate boundary, where the North American and Juan de Fuca plates have been colliding for millions of years. More importantly, due to differences in density, the oceanic Juan de Fuca Plate has been diving beneath the continental North American Plate—a process known as subduction.  

But subduction is not a clean or smooth process.  Anything massive that doesn’t fit under North America is scraped off the oceanic plate and added to the continent. These masses of land, called exotic terranes, are responsible for a good portion of Oregon’s land mass, including Marys Peak and most of the coast range.  

In the case of Marys Peak, the basalt lava flows and overlying sedimentary rock layers formed in the ocean.  Later, as the oceanic plate subducted beneath the western edge of Oregon, magma intruded into these rock layers, forming vertical dikes and horizontal sills of gabbro (like the one that forms the “stubborn” caprock of Marys Peak). As the plate convergence continued, a large block of rock was thrust upward and eastward along the Corvallis Fault. Marys Peak was born!  

The other Coast Range mountains visible from Marys Peak summit are similarly composed of volcanic and sedimentary rocks from the ocean that were thrust upward and over the edge of the continent. And like Marys Peak, many of the other high Coast Range mountains are capped by hard, intrusive gabbro. 

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

Volcanic Peaks

Marys Peak is not a volcano, but from Marys Peak you can see a great many volcanoes. From our vantage point, Bob and I were able to see Mt. Hood, Mt. Jefferson, and the Three Sisters; and, later in the day, Three Fingered Jack, Mt, Washington, Mt. Bachelor, and Diamond Peak. On clearer days you can also see Mt. Rainer, Mt. St. Helens, Mt. Adams farther north; and Mt. Thielsen, Mt. Mazama (Crater Lake), and Mt. McLoughlin to the south. Marys Peak offers views of most of Washington’s and Oregon’s great Cascade Volcanoes! 

I love the Cascade Volcanoes and can’t help but smile anytime I can see them off in the distance. But why are they there? Is there a story beneath the scenery? 

Don’t Sweat! 

Yep! Once again, plate tectonics provides an explanation.

When an oceanic plate subducts, as is occurring off the Oregon Coast today, it starts to sweat!  At about 50 miles below the surface the plate is under so much heat and pressure that it begins to metamorphose and dehydrate. The hot water released reacts chemically with overlying rock, causing it to melt and generate magma. The result is the starting material for repeated volcanic eruptions. 

For the last several million years, the Cascade Volcanoes have been fed by the magma generated by the subduction of the Juan de Fuca Plate below the North American Plate.  The volcanic peaks have erupted countless times during this time period, building up their cone shapes with each eruption.  Though it may seem infrequent on a human timescale, eruptive periods are frequent- with more than 100 Cascade eruptions over the past few thousand years.  As long as subduction continues, the Cascades will continue to erupt. 

Image Credit: Lillie, Robert. “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Wells Creek Publishers, 2017.

The Dynamic Duo: Uplift and Erosion

As Bob pointed out, while tectonic activity is building up volcanoes and lifting up mountains, the other half of a dynamic duo is tearing it all down. The effects of erosion can also be observed at the summit of Marys Peak. 

The Marys Peak region once had an additional two miles of sedimentary rock sitting on top of it!  As the land was lifted up, wind, rain and snow were, at the same time, wearing it down. Sedimentary rock is easily eroded, but Marys hard-headedness—aka her gabbro top—is a big reason she remains tall today. 

The effects of erosion can also be be observed in the Cascade Volcanoes.  When volcanoes become inactive and are no longer being built up by eruptions, they start loosing their tops.  Mt. Washington and Mt. Thielsen are great examples of this. Their pointy tops suggest they haven’t erupted in a really long time, as glaciers have etched away their smooth cones. Yes, even volcanoes show signs of aging!  One the other hand, Mt. Hood’s symmetrical cone shape is a good indicator of “recent” volcanic activity. 

Story of People

After spending several minutes at the top of Marys Peak discussing the “story beneath the scenery,” Bob and I continued our hike, moving downward along the summit trail until we reached the Meadowedge trail junction. Here we took a left and followed the Meadowedge trail. 

Toward the end of that loop, Bob stopped me, suggesting one more time we read the landscape. 

 “What do you see?” He said. 

I looked out across a rolling meadow. But with thoughts of plate tectonics running through my head, I overlooked what he wanted me to see. Finally, he pointed it out- a stage!  

Following WWII, a group known as the Shriners began holding an annual fundraising event on Marys Peak known as the Marys Peak Trek. Each year thousands of people attended to enjoy food and entertainment. One of the meadows even became a parking lot. The damage was extensive. But by 1983, the Trek ended, and the meadows have had some time to start to recover. Even the earthen stage is easy to miss if you aren’t looking for it.  

The Shriners Trek stage.

Bob and I ended our hike by completing the meadowedge loop back to the summit trail, where we hiked through Noble fir forest back to the parking lot where we said our goodbyes.  

Back to the Future

I am not ready to say goodbye to Marys Peak.

Marys Peak still faces many challenges. Rare meadows have been encroached on by Noble fir forest, at least in part due to human disturbance. Social trails and wildflower gathering remain a constant threat to the meadows. And then there is climate change, threatening the very existence of this ice-aged ecosystem.

However, there are also many forces working to preserve Marys Peak. Meadows are being restored and Noble fir populations kept in check. Signs and barriers mark sensitive areas. And many local community groups, like the Marys Peak Alliance, are working to educate visitors on the ecological and cultural importance of Marys Peak.

As we look forward to the future of Marys Peak, it is my hope that it remains as it is today: a future set in the past.

Dr. Robert J. (Bob) Lillie is a free-lance writer, science communicator, and interpretive trainer. Bob was a Professor of Geosciences at Oregon State University from 1984 to 2011. He studied geology at the University of Louisiana- Lafayette and Oregon State University while earning his bachelors and masters degrees, and later studied geophysics at Cornell University where he earned his Ph.D. 

Bob has written extensively about Pacific Northwest geology in “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest” and “Oregon’s Island in the Sky: Geology Road Guide to Marys Peak.” Both books are available at area bookstores, museums and visitor centers, as well as on amazon.com

Run Around the Alvord Desert: Let’s Playa

The Alvord Desert Playa

With the walls closing in at home, my family and I decided to head out to the Alvord Desert for some much needed solitude and wide-open space for a weekend in mid-May. The plan was to camp for a couple nights, and hike and explore during the day. The Alvord Desert is on BLM land and primitive camping is allowed. So, with the promise of room to roam, we packed up our vehicle with the necessary provisions, loaded up the car, and headed southeast. 

Alive in the Alvord

The Alvord Desert is a playa located on the east side of Steens Mountain- a huge fault block mountain that runs for miles at the edge of Oregon’s Basin and Range region. Dry and expansive (about 11 miles long and 6 miles wide), with a cracked earthen floor. The Alvord Desert landscape feels alien- devoid of greenery and seemingly lifeless; a monotonous swath of dirt and dust. Much like what you would expect from a desert.

But then…

You watch the sun rise and fall, casting shadows and painting the sky intermittently between hours of moon and stars and wind. You roam the sagebrush boundary lands, hunting for lizards or other desert life. When the sun is high and the heat is too much, you swat away invertebrates while reading the book you brought on the trip, moving every once in a while in order to remain in the shade. On your early morning run, you discover large pools of water that make you reflect on what you know about hydrology (more on that later). And suddenly, you find yourself waxing poetic about this mysterious landscape called the Alvord Desert… Or maybe it is just me.

Arrival 

After driving for countless miles, my family and I arrived in Alvord Desert late in the afternoon. It was finally cooling down for the night, when we found a spot to camp on the edge of the playa. There, we spent the evening watching our shadows grow long and once night hit, we counted stars and waited for the moon to rise. Eventually, one-by-one, we fell asleep to the sound of the desert winds, visions of wide-open-spaces dancing in our heads.

The Hike or Run 

  • Trailhead: any place you can find your way back to (make sure you know your return coordinates)
  • Distance: any distance your energy level will allow
  • Elevation Gain: virtually none
  • Notes: Run or hike from virtually any point you would like. Bring plenty of water. Distances appear shorter in the desert, so plan accordingly. Make sure you know where you are starting from, so you can make it back safely.
Heading out on a sunrise run.

A Glass Half Full 

At first light, I was up and ready to explore. My plan from the get-go was to run the playa: so much space and nearly level ground- a distance runners dream, I thought. So I donned my running gear and started to move. The light of the early morning was magic, as I trotted along at my usual slow pace, soaking in the atmosphere. I followed the shrub-lined edge of the playa for most of the run. It was eerie and peaceful.

Eventually, I made it around to the opposite side from camp and figured I would cut across the playa when- splash- water! What I had thought was a desert mirage, was actually a thin lake of water that made crossing the playa at that point impossible.

Rerouting my run, questions began to soar through my mind about the wet encounter. I had read that the Alvord desert had a wet and dry season, but for some reason it didn’t fully register until that moment; until I ran smack into it.

Tired and a bit dehydrated from my run, I thought a lot about the hydrological cycle of the Alvord- about its cycles and seasons- and decided I needed to know more about this unique land of wet mud and dry dust.

Ready? Let’s Playa in the Alvord!

The Alvord Desert covered with a thin layer of water

In the Shadow

Lying within the rain shadow of Steens, the Alvord Desert is considered the driest place in the State of Oregon, receiving only about 7 inches of precipitation per year. As part of Oregon’s interior, not a lot of moisture makes it to this southeastern region. And what little does makes it into the region, is removed from the atmosphere as snowfall on Steens Mountain’s western flank. This process is known as the rain shadow effect. When moisture laden air travels up a mountainside (the windward side), it cools, condenses, and eventually falls as precipitation. The dry air then continues down the other side of the mountain (the leeward side), where it heats up, encouraging further drying through evaporation.  The Alvord Desert is on the leeward side of Steens, so it not only gets little rainfall, but it experiences a lot of evaporation.

Dry and Cracked 

Additionally, the Alvord basin, like most watershed in the Basin and Range of Oregon, is a closed-watershed system. Instead of taking a more traditional route to the Ocean, water in the Alvord doesn’t leave by surface or groundwater flowing to the Ocean. Instead, it stays in the basin until the hot sun evaporates it away. The result is another interesting features of the Alvord- cracks.

Alvord Desert’s surface is riddled with geometric shapes separated by cracks. Known as desiccation fractures, these cracks form as the surface of moist clay-rich sediments dry and shrink through sun and wind evaporation. Shrinking results in tensile stresses that radiate out in all directions on the surface that ultimately break, resulting in polygonal cracks- one of the Alvord Desert’s characteristic features.

Desiccation Fractures

Reflecting on a Thin Film of Water

O.K. so that explains why it is so very dry in the Alvord Desert, but it doesn’t explain why there is water there at all.  Where does the water come from, if not from precipitation?

Perhaps not surprisingly, much of the water in the Alvord Desert comes from higher up- on Steens Mountain.  Steens Mountain captures a lot of precipitation in the form of snow. Later in spring, the snowpack melts and feeds streams and groundwater systems that supply water to the basin below. Much like how water accumulates in the drain at the bottom of your sink, the Alvord Desert is one of several low points, separated by alluvial divides, that capture water draining from Steens above. 

Steens Mountain

Shifting Waters

However, as a desert playa, the Alvord Desert also happens to be very large and very flat. In the spring, expansive areas fill with water but at a depth of only a few centimeters. It is the process of inundation that actually helps maintain the flatness of a playa- laying down sediments evenly throughout.

When visiting the Alvord Desert it is important to remember that these thin, but massive lakes of water may grow or shrink, and/or shift, making parts of the playa potentially impassable at times. During my morning run on the playa, it was just a matter of rerouting, but there is potential for getting stranded by these shifting waters. In the Spring, when water levels are wide, the risk of getting trapped by pooling water is particular high, so plan accordingly.

An Ancient Lake

However, even during its wettest season, the thin surface water of the Alvord is nothing compared to the amount of water it once held during its tumultuous past. From about 3.5 million years ago to 15,000 years ago, recurring ice ages increased rainfall in southeast Oregon that filled the large basins characteristic of the region. The Alvord Desert and surrounding sub-basins (as far south as Nevada) were all connected as one massive pluvial lake. Filled to the brim, Pleistocene Lake Alvord had a depth of nearly 200 feet at one point, and would often overflow. 

Overflowing

During periods of overflow, water would travel via Crooked Creek to the Owyhee River.  During one cataclysmic event, water burst through Big Sand Gap on the lake’s eastern rim, eroding it down about 12 m, and sending torrents of water into the much smaller Pluvial Lake Coyote, through Crooked Creek, and out to the Owyhee River. Today along Crooked Creek, you can observe the scabland terrain and boulder bars that serve as evidence of this event.  Apparently, you can also hike out to Big Sand Gap from the Alvord Desert by following wild horse trails to see the breach up close- something I will have to try on my next trip.  

It wasn’t until the last 10,000 years that the Earth warmed again and the Alvord became the desert you see today. 

Alvord Desert at sunrise

You Should Go Playa

Whether you explore on foot or otherwise, the Alvord Desert is a magical place to visit. It may look one-dimensional at first glance, but if you stay awhile, the dynamic nature of the landscape, with it’s subtle shifts and movement, begin to unfold. You should seriously go “playa” in the Alvord- you won’t be disappointing. Just don’t forget the moisturizer.

  • “Alvord Desert – The Oregon Encyclopedia.” 20 Mar. 2018, https://oregonencyclopedia.org/articles/alvord_desert/. Accessed 26 May. 2020.
  • “Playa | geology | Britannica.” https://www.britannica.com/science/playa. Accessed 26 May. 2020.
  • Tanner P.W.G. (1978) Desiccation structures (mud cracks, etc.). In: Middleton G.V., Church M.J., Coniglio M., Hardie L.A., Longstaffe F.J. (eds) Encyclopedia of Sediments and Sedimentary Rocks. Encyclopedia of Earth Sciences Series. Springer, Dordrecht.
  • O’Connor, Jim E., Rebecca J. Dorsey, and Ian Madin, eds. Volcanoes to vineyards: geologic field trips through the dynamic landscape of the Pacific Northwest. Vol. 15. Geological Society of America, 2009.
  • “Oregon: A Geologic History – Oregon Geologic Timeline.” https://www.oregongeology.org/pubs/ims/ims-028/timeline.htm. Accessed 26 May. 2020.

Hike with a Volcanologist

Upper Shellburg Falls

Entering the Blast Zone

The skies were clear blue as I headed out to meet with volcanologist Mariah Tilman for our hike at Shellburg Falls.  In the distance, I caught a glimpse of snow capped Mount Jefferson, the second tallest Cascade volcano in Oregon.  Though we weren’t going to get up close to this behemoth during our hike, I wondered if our walk in the foothills of the Cascades might offer a glimpse into Jefferson’s power.  What forces are responsible for the formation of the Cascade peaks? Are these same forces at work in other parts of Oregon? Would we see any evidence of past volcanism during our hike through a humble state forest? Little did I know, I was about to enter the “blast zone” when it comes to volcano knowledge.

The Hike

Hike at a Glance

Trailhead: Shellburg Falls Trailhead

Distance: about 2.8 round trip. Out and back trail.

Elevation Gain: about 400 feet

Notes: There is no restroom at the trailhead. Parking is limited. Part of the hike is on private property so stay on trail. There are many variations to this hike with options for more mileage.

Mariah Tilman on the Shellburg Falls trail.

Volcanology Basics

The Shellburg Falls trail begins on a road through private pasture land before entering the forest.  As we made our way through this area, Mariah and I talked a bit about what it is like to be a volcanologist, as well as why the profession is so important.

Of course, the job of a volcanologist is to study volcanoes.  There are five USGS volcano observatories, all found in the western U.S., including the Cascades Volcano Observatory in Vancouver, WA. The main goal of these observatories is to monitor volcanic activity in order to predict and assess the risk associated with volcanic eruptions. 

How do they do it?  According to Mariah, there are a lot of tools a volcanologist will use to size up volcanic risk.  Among the most important tools are seismometers. These can be placed throughout the landscape in order to detect movement of the earth, and give us an idea of what is happening below the surface.  Another tool that is used is satellite imagery. Satellite imagery can be especially useful in monitoring the activity of volcanoes in remote areas, like Alaska, which has 52 active volcanoes, most of which are part of the hard to reach Aleutian islands.  

Safety First

Public safety is the primary reason we study volcanoes. Besides the threat of lava and pyroclastic flows near the erupting volcanic vent, lahars- a hot mix of water and volcanic debris- can travel dozens of miles.  If an eruption occurred during our hike, a lahar from Mt. Jefferson could easily travel far enough to reach us and neighboring towns. Yikes!

Then there is ash.  Ash has the ability to travel large distances causing widespread disruption of natural and human systems.  As Mariah explained, ash can be especially problematic for air traffic. In 1989, two jetliners nearly went down in an ash cloud generated by the eruption of Mount Redoubt in Alaska.

Fortunately, since the famous Mount Saint Helens eruption of 1980, scientists are better equipped to monitor and predict volcanic eruptions, sometimes even a year in advance.  Given enough warning, communities can at least prepare for the onslaught.

With Mt. Jefferson looming “a little too close for comfort,” I asked Mariah if we should be concerned about it erupting.  She reassured me that none of the Cascade peaks are currently predicted to erupt anytime soon. Phew!

It’s All Downhill

A small pile of angular rocks found along the trail.

As we made our way into the forest, we encountered our first geological phenomenon- the remnants of an old landslide.  Landslides occur when the shape of the land, climate, and geology work in concert to weaken the connection between overlying sediment and material beneath.  When this occurs, gravity takes over, moving earth materials downhill where they accumulate. Though people often think of geology as the building up of land through plate tectonics and volcanism, the wearing down of the land by weathering and the movement of land by erosion, are also important geological processes. 

But how do we recognize a wearing down process, like a landslide, in nature?  What can we observe to understand the geological activity of a place? I asked Mariah what to look for.  

Think like a Geologist

She explained, one of the best ways to begin thinking like a geologist is to look for patterns in the landscape.  Differences in the landscape are important evidence to understand the geology of a place. Though the area where the landslide had occurred in the past was now overgrown with trees, moss, and other vegetation, Mariah pointed out that the shape of the land had changed.  

There were other landslide clues as well. First, Mariah and I observed many large rocks strewn about the base of the hillside. Unlike in a river, where sediments are sorted by size as the river loses energy downstream, rocks in a landslide lose energy abruptly, falling into a jumbled piles.  Second, the shape of the rocks was angular. Landslides happen quickly, so rocks in a landslide will be angular, instead of worn down and smooth.

Hotspot or Subduction?

Rock outcropping along the trail.

As we continued our hike past the landslide, the shape of the land changed again . We started noticing outcroppings or rock of unknown origin to the left of us. Mariah and I began to speculate-  How did these rocks form? Where did they come from?  

Mariah narrowed down the source of these outcroppings to two likely possibilities.  First, about 16.7 to 5.5 million years ago it is believed that the Yellowstone hotspot was under the Oregon-Idaho-Nevada border.  This hotspot resulted in huge floods of basalt lava to cover large swaths of Oregon.

Secondly, about 35 million years ago and again 7 million years ago, tectonic activity along the Cascadia subduction zone built up the old and new Cascade volcanoes.  Subduction occurs when an oceanic plate plunges beneath an overriding plate. As the descending plate heats up in the mantle it “sweats,” resulting in a build up of gases and pressure- the perfect conditions for explosive volcanic eruptions characteristic of the Cascades and other stratovolcanoes.  

Igneous Rocks, Rock!

The dark color of these rocks are a clue that we are looking at basalt.

Though Mariah wasn’t 100% sure the origin of the rocks in the Shellburg Falls area, one thing was certain- these were igneous rocks.  In general, rocks can be classified as igneous (molten rock that has cooled), metamorphic (rock that has been subjected to intense heat and pressure), or sedimentary (rock formed from compacted sediments).  However, rocks can also be further described and classified depending on how they formed and their mineral content.  

Rocks formed from hotspot volcanism, for example, are typically basalts, with high amounts of iron and magnesium and low amounts of silica minerals, giving them a dark color.  In contrast, rocks like rhyolite, that are formed through subduction volcanism, have a higher amount of silica content, making them lighter in color. So rock color is a clue to the mineralogy, which in turn is a clue to rock formation. 

Broken rock with large weathering rind.

However, Mariah warned, be careful of broad generalizations. Stratovolcanoes (those formed by subduction) actually form many types of rocks during their activity, including basalt.  Also, the color of rocks can easily be distorted by weathering, making it difficult to identify the mineralogy based solely on color.

Count the Minerals

In order to effectively classify an igneous rock, you need to look at the mineral composition more closely.   Basalt by definition should only be 49-50% silica, rhyolite should be 70-75%, with andesite falling in-between. Unfortunately, in order to get down to percent composition that requires magnification. Without a microscope in the field, using color and shape are often the best one can do.

With that in mind, and after cracking into a rock to get a better look at its color, we came to a conclusion that the outcroppings were probably basalt.  Left in uncertain agreement, we hurried up the road. 

Crystal Clear

Outcropping of rock found near the Shellburg Creek bridge.

Soon, we reached the bridge that leads over Shellburg Creek, just above lower Shelberg Falls. To the left, was a large outcropping of igneous rock. At Mariah’s suggestion, we stopped to examine the rocks here.   

However, rather than trying to identify them, Mariah began searching the rocks for crystals. Mariah explained, in order to really understand the life of an igneous rock, knowing the type is not good enough- you have to look at the crystals!

A bit like tree rings provide the life history of a tree, crystals provide a record of where and for how long the magma the crystal formed in spent underground. Different crystals will form in magma depending on its temperature and depth. For example, olivine- a green colored mineral- forms at high temperatures and depth.  While quartz forms at low temperatures and shallow depths.

Perhaps the most notable crystals that form in magma are those called plagioclase feldspars. The chemical composition of these crystals will change depending on temperature. Deep in the ground under high temperatures they are calcium rich, but as the crystal grows closer to the surface, calcium is gradually replaced by sodium. The results are concentric rings of crystals with different amounts of sodium and calcium that offer a record of the magma’s movement before an eruption. 

Unfortunately, we didn’t find any distinct crystals in our wall of rocks, only some small grains. It seems the magma that formed this particular outcropping did not spend much time underground. 

Right before the outcropping is a small dirt trail to the left that leads to upper Shellburg falls. We retraced our steps back a few yards to this junction and made our way onward toward our final stop- the falls.

Free Fallin’

As we walked along Shellburg creek, we could see large boulders of rock in the creek below.  Where did they come from? These boulders were likely the remains of an old waterfall overhang- “old Shellburg falls.”

You see, waterfalls form when a hard rock overlays a soft rock.  In the case of Shellburg Falls, basalt rock sits on top of sedimentary rock. The softer rock erodes over time creating a waterfall overhang.  With enough weathering, the overhanging rocks stability can become compromised resulting in collapse. This process of weathering and collapse means a waterfall is always moving further upstream over time.

We would need to move further upstream to see”new Shellburg falls.”

Blanketed in Basalt

Shellburg Falls- notice the distinct layers of igneous and sedimentary rock. A large boulder to the left may have once been part of a past waterfall overhang.

Before long, Mariah and I were in full view of the waterfall. The hard igneous rock cliffs that line the canyon, and form the waterfall overhang, stood out beautifully against the sedimentary rock below it. 

But wait, look at the rocks to the left! The left wall of the canyon showed a familiar jointing pattern- columnar basalt! Columnar basalt looks sort of like a pipe organ, but with hexagonal pipes that aren’t pipes at all, but columns of lava rock.  This pattern of basalt is the result of slow cooling, cracking, and contracting. Columnar basalt is not only useful for identifying rock as basalt, but it is a geological wonder in many regions around the world.

Columnar basalt

Ancient Waters

The cavern behind the falls

Things got even more interesting, as we made it into the large cavern behind Shellburg falls. From here, you could see how the soft sedimentary rock had been worn away below the basalt cliffs.  However, rather than looking up at a ceiling of hexagonal columns of basalt like that observed outside the cavern, large bubbles of rocks protruded down towards us. We found pillow basalt!

Pillow basalt forms when lava flows into water and cools there.  That means the location of present day Shellburg falls was once the location of another ancient body of water. Not only that, but this ancient body of water probably existed for some time. The sedimentary layer below the basalt was thick; it must have taken a good deal of time to collect so much sediment- possibly millions of years!  

Pillow basalt

According to Mariah, the geological history of Oregon is not very long compared to other areas of the country.  Oregon is young geologically speaking. Yet, so much has happened to take us up to the current day. Oregon of the past was a fiery furnace with lava flows and explosive eruptions; it faced deluges of water & ice; and experienced many changes in climate and weather.  It has been built up and torn down countless times by the forces of nature. And it is just beginning! The ancient body of water that existed in the past may be long gone, but give it a few million years and Shellburg Falls will look completely different.  

Rock on!

After continuing to the other side of the falls for a different perspective, Mariah and I decided to head back to the trailhead.  Who knew that in just a few miles of trail, one could see so many signs of geological activity. From landslides to lava flows, from weathering to the formation of crystals, you don’t need to visit a volcano to see the drivers of geological activity in Oregon.  Just pay attention to the landscape. And maybe pick up a rock or two.  

Mariah Tilman is a volcanologist and igneous petrologist. She studied volcanoes at the University of Alaska, Fairbanks.  In addition to volcanology, she also has a background in hydrology and water quality. She currently teaches Geology of the Pacific Northwest among other classes at Chemeketa Community College and Portland Community College. 

Hike with a Snow Scientist

View up Potato Hill trail from trailhead.

Here Today, Gone Tomorrow

Ah, snow— tiny frozen ice crystals falling from the sky.  Snow is amazing— chillingly beautiful and fun to play in. Great for skiing, snowshoeing, sledding, and don’t forget building snowmen.  But most of the world’s snow is ephemeral. It is like a holiday, or romantic tryst—magical at the moment but doesn’t last.  

However, it is the ephemeral nature of snow that perhaps makes it so vital.  The fact that snow hangs out for a while on the landscape is one of the most important features of snow. How snow accumulates, shifts and changes form, and eventually melts away, significantly influences the ecology, hydrology, and natural resources of the land. 

Change

Christina Aragon on the top of Potato Hill.

While snow is a great influencer, it is also greatly influenced. From its start as a snowflake falling from the sky, its fate depends on a host of environmental factors. Just a little nudge in temperature, or a small shift in humidity, and snow will change. It may fall as sleet, or turn into rain. It may not accumulate or melt early.

Concerns around changing snow, brought me to reach out to Christina Aragon, snow hydrologist and Ph.D. student at Oregon State University. After seeing her speak at a TapTalk in early February 2020, I HAD to see if she would be up for a snowshoe with me. She agreed. And before the month was up, we headed into the Cascade Mountains to find some snow.  

The Hike

  • Trailhead: Potato Hill Sno-park
  • Distance: 3.5 miles, with a possible 5+ mile loop option by adding the forested Hash Brown Loop.
  • Elevation Gain: about 800 feet
  • Notes:  Sno-pass is required for parking. There is no restroom at the trailhead. The parking lot is not huge. Snowshoe route follows Jack Pine Road.  The elevation is 4,200 feet.

Special as a Snowflake 

We arrived at the Potato Hill Sno-park late in the morning.  The snow was falling as we strapped into our gear. It was still falling as Christina and I began our steep ascent through the white and drifted snow.  

We had gone no more than a few 100 yards when Christina wistfully reached out and caught a few snowflakes on her glove. I leaned in closer to have a look. Christina explained as I tried to make the details in the tiny crystals on her glove that, though each snowflake is unique, snowflakes can be classified by their shape.

Different snowflake shapes will form depending on the temperature and relative humidity in the atmosphere. The snowflakes that were falling while we headed up potato hill were mostly clusters of needles.  Needles, which look a lot like their namesake, form when the temperature is relatively warmer and humidity is at mid-range.  

Christina also caught a stellar dendrite in flight, but it quickly melted into her glove. 

Stellar dendrites look more like a classic snowflake- flat with six intricate lace arms coming out from a center.  Stellar dendrites will form when humidity is higher and temperatures are a bit warmer, or if the humidity is really high, but temperatures are cold.  (They also form when you combine a six-year-old with a white piece of paper and scissors, but I digress.)

Several different snowflakes can fall at one time, but usually, one type predominates.

Other snowflake shapes include columns, capped columns, and six-sided plates.

Also, keep in mind snowflakes are small, defined as a single crystal.  If you are looking out the window at what appear to be large fluffy snowflakes, these are actually clumps of snowflakes falling together. This occurs when flakes fall and start to warm up, melting into each other.  

What’s the Graupel?

Not all ice falling from the sky is snow or made up of snowflakes.

Graupel is another form of falling ice crystals.  Graupel forms when a falling snowflake collects supercooled water droplets on its surface forming a large (2-5 cm) rounded pellet.  Though not a snowflake, graupel is a type of snow.

In contrast, sleet is not snow because, though it may start as snow, it melts and refreezes into ice.

Who knew that just defining snow would be so complicated? 

A slice of snow cake

Christina digging a snow pit.

Up the tree-lined road, we continued walking along what felt to me like very stable snow.

Just a couple of weeks ago, I had been snowshoeing through snow that was very unstable. That got me wondering—Why was that? What happens to snow once it reaches the ground? Why was the snow today such a pleasure to walk on compared to before? I asked Christina for the skinny on-ground snow. 

Once the snow falls to the ground, like a caterpillar in a chrysalis, it begins to undergo metamorphosis (though the change is less predictable than you get with a monarch). The best way to see these changes is to dig in and look at the layers.

Digging a snow pit reveals a snow profile.  A snow profile serves as a record of events in the “life history” of the snowpack. It can also help you determine its stage of metamorphosis—is it becoming more or less stable, for example? So that is what we did.

Our snow profile revealed fairly stable snowpack conditions.  By running a finger or two through, and into, the snow layers, we were able to identify a softer “new snow layer” and a deeper layer of very “stable rounds”. 

Snow profile testing.

Rounds or Facets

Rounds dug from the lower portion of the snow profile.

New snow layers still retain some of their original crystalline shapes and are less dense. While deeper in the snow, either rounds or facets will form depending on the temperature gradient.

Rounds form in snowpack when the temperature range through the snow is pretty similar throughout the snowpack, or isothermal.  When the temperature gradient has more than a 1 ° C change for every 10 cm of the snowpack, this is a sign that facets are forming.

Facets are unstable and can lead to avalanche danger. Unlike rounds that have sinters that hold the snow together, facets are large and angular with points and don’t stick together well. Imagine “sticking your finger into sugar” and that is kind of like what facets feel like, explained Christina.

Rain Crusts

In addition to the two main layers, our finger test revealed a small rain crust in our snow profile. Rain on snow is a source of latent energy, as the liquid water freezes on the snow, energy is released into the snowpack.

A rain crust can also change the movement of water through the snow. Instead of water flowing vertically through the snowpack and into the soil below, water can flow horizontally through the snowpack along the ice layer.

One of these Snow is not like the Others

In the Cascade Mountains, having a stable snowpack is actually the norm compared to other places in the U.S. Snowpacks in maritime snow climates, like the Oregon Cascades, generally form right at freezing temperatures, building deep, dense, wet snowpacks. In continental mountain ranges, like the Rockies, temperatures are much colder, and the air is much drier creating a shallow, less dense snowpack. Think fluffy “champagne powder.”

The maritime climate of Oregon’s Cascades results, not only in relatively warmer, but much deeper and denser snowpack. Warm moist air is carried inland from the west, sometimes on huge atmospheric rivers, and pushed up over the Cascade Mountains- this is called orographic lift.  The result is that as this air rises, it cools, and the moisture is squeezed out as rain or snow.  

Losing Structure

The unstable snowpack I experienced a few weeks ago, was probably due to a loss of structure that can occur with mid-season melt (another very Oregonian snow predicament). In this case, mid-season melt probably caused most of the sinters that hold the rounded snow together to melt away. The remaining snow was more like a loose collection of rounded pebbles of ice with very little strength.

Snow on Fire

The transition from forest to burn area.

Nearing the top of Potato Hill, the scenery changed from snow-covered trees to more open terrain. The B&B Complex fire of 2003 burnt down much of the forest in this area.  

Observing snow in burnt forest areas, was one of the ways Christina first became interested in studying snow.  In B.C., when one of her favorite forested snow recreation areas was burnt, she noticed that the snowpack was gone MUCH earlier than before the fire. Christina was later able to work with Dr. Kelly Gleason on a research project that explained the phenomenon.  

Black Snow

Burnt trees from B&B Complex fire.

We hiked up to one of the burnt trees on Potato Hill where Christina pointed out its charred bark. She explained how black carbon and micro-charcoal particles from trees and other sources end up in the snow following a burn. 

Snow normally is very reflective of the sun’s rays—it has a high albedo. However, as dark particles accumulate on snow’s reflective surface, instead of bouncing back, the rays get absorbed by the black carbon, heating up and melting the snow!  

We dug into the snow to see if we could see the particulates in the snow on Potato Hill.  Despite the fire being over 10 years ago, the snow still looked dirty with particulates. 

Snow profile taken in burned area.

More Melt

However, black snow is only one factor that affects snowmelt in the west. Climate change is causing shifts in both the quantity and timing of snowfall in the western United States. Many places in the west are already seeing a decline in snowpack and a shift to earlier spring snowmelt, trends that are expected to continue.

This is a huge problem! Snow is a reservoir for our water supply—storing water for later in the year when we need it.  In the western U.S., about 70% of our runoff originates with snow. With the timing of snowmelt shifting to earlier in the year, runoff is making it into our valleys too soon, and we don’t have the supply we need for later in the year. 

A Vicious Cycle

Less snow means less reflection of light from the sun (lower albedo), which means more heat absorption and more melting—a vicious cycle.

Earlier melting of snow also results in dryer forest soil in the summer and a longer fire season, which means more black snow and more melting. Another vicious cycle.  To make matters worse, the effects of black carbon on snow are not short-lived either—lasting 10 years or more. 

Snow Measurement

Break at the summit- what a view!

Pelted by crystalline water droplets, Christina and I reached a “viewpoint.”  Here we stopped to celebrate with pictures and a snow depth measurement.  

A big part of Christina’s Ph.D. work involves improving models of snow distribution in mountainous and remote places in order to better understand water resource availability during the year.  In order to do this work, good reliable snow data is needed. In particular, she needs to know the SWE of snow. SWE is snow water equivalent, the amount of water contained in the snowpack, and is based on snow depth x snow density.  

Measuring SWE is not easy to do and involves heavy equipment that most people don’t want to carry in their packs.  So instead of measuring SWE, Christina encourages and promotes a citizen science project called Community Snow Observations.  Data gathered by the project is used to validate data gathered remotely and improve snow models. And the best part is it is easy.  Using an avalanche probe, or even a ruler, you take several depth measurements, average them, and then report the value using an app. 

Christina measuring snow depth.

Become a Citizen Scientist

Finding SWE from depth using both ground and remote sensing technologies is a hot area of research in the hydrology world.  It is also research anyone can get involved in. If you want to do your part visit communitysnowobs.org to learn more. 

 Shifting Snow

On our way back down the hill to the car, Christina and I talked more about what to look for when in a snowpack environment.  

The distribution and build-up of snow on the ground are always in flux, which can make it both extremely interesting to explore, as well as very complex and hazardous.  Here are a few variables to consider while hiking in the snow. 

Snow inception on trees.

Number 1- Trees. 

The effects of trees on snowpack are complicated.

Trees can intercept snow, preventing it from reaching the ground where it accumulates, and increasing rates of sublimation, the direct transition of snow to water vapor. When branches of a tree are wide with low hanging branches, like most conifers this can also result in the formation of dangerous tree wells.

Trees also emit longwave radiation, like other dark objects, making the snow around trees slightly warmer than open areas, which may lead to more melting, particularly at the tree’s base. However, at the same time, forests block a lot of incoming solar radiation from reaching the forest floor, slowing down snowmelt in many forests.

Number 2- Wind. 

The wind moves snow around a lot.  Where the wind is going and coming from changes the profile of the snowpack—making it more shallow in some areas, and in others really deep and hazardous.  Wind loaded slopes are a real avalanche danger that can occur on downward slopes where wind piles up snow. Wind scoured slopes, like the top of a peak, will have a shallow profile and can be difficult to travel on. 

Number 3- Elevation

In general, the higher up you are in elevation the more snow will accumulate (with the exception of peaks scoured by high winds).  Snow profiles deepen at high elevations and may present more layers. Thus, to understand the snowpack in an area, it is generally a good idea to dig snow pits at multiple elevations and locations. 

Number 4- Aspect.

North-facing slopes receive less solar radiation than south-facing slopes.  Even on a small scale, once the snowpack enters the ablation period, where it is melting off, south-slopes will melt off faster.  

Number 5- Slope Angle.

One of the easiest factors to keep in mind when considering potential hazards in a snowpack area is the terrain.  Steeper slopes are much more prone to avalanches. If your slope is between 20-25 degrees or less, your risk of avalanches drops significantly. 

Let it Snow

Phew!  That was a veritable blizzard of snow information!  So don’t let it melt away. Instead, hit the snowshoe trail, catch some snowflakes, dig a snow pit or two, measure the snow, or simply watch the snowfall. And next time you take a shower or sip your favorite beverage, think about those cool white flakes. Because odds are, that liquid you are enjoying, first fell as snow! 

Christina Aragon is a Ph.D. student at Oregon State University studying hydraulic modeling.  Originally from Denver, Colorado, she has experience in avalanche operations and snowboarding.  She got her undergraduate from the University of British Columbia where she studied kinesiology and ecology. She got her master’s in Geography from Portland State University where she studied hydro-climatology.