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Smith Rock State Park –great geology at the edge of Oregon’s largest caldera

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Smith Rock, the Crooked River, and modern Cascade volcanoes from Misery Ridge.

The view from outside the small visitor center at Smith Rock State Park offers a landscape of contrasts. The parking lot, and nearby camping and picnic areas, are flat, underlain by the edge of a basaltic lava flow that drops off in a series of steps to a narrow canyon, some 120 feet (37 m) below. The Crooked River, which rises about 100 miles (162 km) away in the High Lava Plains, fills much of the canyon bottom. Across the canyon, tan cliffs and spires of tuff, another volcanic rock, soar overhead. Smith Rock itself forms a peninsula of this rock, enclosed by a hairpin bend of the Crooked River. The tuff erupted 29.5 million years ago in the largest volcanic eruption to occur entirely within Oregon.

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View down the Crooked River from near the parking lot. On the left is the Newberry basalt flow; the reddish tower just right of the river is the rhyolite dike intruding the Smith Rock Tuff.

The eruption created the gigantic Crooked River Caldera, which stretches like an ellipse southeastward from Smith Rock more than 20 miles (32 km) and traversed along its length by the Crooked River. Around its perimeter are rhyolite bodies that intruded after the eruption along ring fractures surrounding the caldera. These rhyolites include Gray Butte, just north of the park, Grizzly Mountain, to the northeast, and Powell Buttes, some 15 miles (24 km) to the southeast. The imposing red-colored tower, just downstream from the hikers’ bridge in the state park, is a rhyolite dike that also intruded after caldera collapse.

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Geologic maps: of Smith Rock State Park (left) and the Crooked River Caldera (right). Compiled from McClaughry et al. (2009A), Robinson and Stensland (1979), Walker and MacLeod (1991), and the State Park trail map.

Some of the finer-grained, airborne material likely accumulated 75 miles to the east to form much of the green-colored Turtle Cove Member of the John Day Formation, which has the same age. All told, the eruption produced more than 140 cubic miles (580 km3) of material. The eruption size as well as its caldera, however, eluded detection until about 2006 when Jason McClaughry and Mark Ferns of DOGAMI completed detailed mapping of the region. Now, some researchers even consider the eruption to be an early phase of the Yellowstone hot spot!

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Much of the green Turtle Cove Member of the John Day Formation, so well exposed at John Day Fossil Beds National Monument, was probably derived from alteration of ash derived from eruption of the Crooked River Caldera, 29.5 million years ago.

Hiking any of the state park’s numerous trails gives you plenty of chances to see the rock close-up. It’s pretty much all tuff, the volcanic rock made mostly of consolidated ash and pumice. Many tuffs become welded into hard rocks because of the high temperatures as they compact, but most of these tuffs are not welded and so relatively soft. Some exceptions include the red-colored welded tuffs at the crest of the Misery Ridge trail.

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Close-up view of the Smith Rock Tuff. The faint green layers contain a higher proportion of fine ash, whereas the intervening areas typically contain coarser ash and more pumice. The greenish color consists of the alteration mineral celadonite.

You might also notice that parts of the cliffs display layering inclined roughly southward. Up-close, you can see that some layering is defined by subtle changes in the proportions of fine to coarse ash to suggest variations in the ferocity of the eruption. Many layers contain small rock fragments, the rocks being older material incorporated into the eruption. Most of these rocks are volcanic, derived from the underlying Clarno Formation. A tiny fraction, however, are pieces of Permian-age limestone. These limestones are significant as they came from the basement rock, accreted to North America during the later Jurassic or early Cretaceous periods.

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Fine-scale layering in the Smith Rock Tuff

Numerous pocket-like holes dot many of the cliff faces. The outer edges of these features typically consist of more durable rock whereas the insides typically consist of softer, more easily erodible material. The durable crusts form because minerals in the tuff dissolve in pore water and re-precipitate on the surface as the pore water evaporates. At Smith Rock, the responsible minerals are mostly zeolites, a group of minerals with wide-ranging compositions but containing silica, aluminum, and water. Along with the enhanced weathering and erosion along fractures, this case-hardening results in an endless variety interesting shapes and pinnacles.Case-hardening in tuff

The case hardening also creates outstanding surfaces for climbing, so on sunny weekends, the state park draws hundreds of rock climbers of all abilities. Considered one of Oregon’s top climbing areas, Smith Rock offers more than 1500 routes. Moreover, the cliffs are recognized as the birthplace of American sport climbing, which unlike traditional climbing, benefits from anchors placed permanently in the rock

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Rock climber reveling in a crack on the pillar called “Monkey Face”. Note the reddish upper part of the rock –it’s welded tuff above the non-welded tuff. Note also the layering in the tuff.

IMG_2255lrcThe basaltic lava flows at the state park have their own story, as they originated from vents on the north side of Newberry Volcano some 400 thousand years ago. If you look closely at the basalt, you’ll see that it’s uniformly very finely crystalline, but in some places full of air bubbles called vesicles. Because gases tend to rise through lava flows, the vesicles tend to become larger and more abundant towards the top of individual flows–as shown in the photo on the left –although you really need to click on it to see the larger version. The photo is 4 feet high from bottom to top.

For the most part, the lavas covered the older Smith Rock Tuff. They blanket the southwestern part of the caldera and sit on top the tuff in many places within the canyon. However, the cliffs of Smith Rock soar far above, so the lavas had to flow around them on their way to the Deschutes Canyon, some ten miles to the northwest. The interface between the high-standing tuff and the basaltic lava must have been highly irregular to make it ripe for erosion by the Crooked River, which now meanders through a lovely gorge.

And this post! It’s a draft of an entry I’m planning for my upcoming book, “Oregon Rocks!” –to be published by Mountain Press, probably sometime in 2021. I’m only allowed a few photos per entry, so here are a few more! You can click on each to see them at a larger size.


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Newberry Basalt overlying Smith Rock Tuff on the west side of the Crooked River, just downstream from its hairpin bend. Note the channeled base of the basalt.

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Lithic (rock) fragments in the tuff

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View northward from the west side of Misery Ridge, showing the red-colored welded part of the tuff overlying the less welded part.

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Contact of ash-and pumice-rich tuff overlying lithic-rich tuff near the bottom of the Misery Ridge Trail.

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View upstream: tuff on the left and in the background; basalt in the right middleground.

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Some useful references:

Bishop, E.M., 2003, In search of ancient Oregon: Timber Press, Portland, 288p.

McClaughry, J.D., Ferns, M.J., Gordon, C.L., and Patridge, K.A., 2009A, Field trip guide to the Oligocene Crooked River caldera: Central Oregon’s Supervolcano, Crook, Deschutes, and Jefferson Counties, Oregon, Oregon Geology, v. 69, p. 25-44.

McClaughry, J.D., Ferns, M.L., Streck, M.J., Patridge, K.A., and Gordon, C.L., 2009B, Paleogene calderas of central and eastern Oregon: Eruptive sources of widespread tuffs in the John Day and Clarno Formations, in O’Connor, J.E., Dorsey, R.J., and Madin, I.P., eds., Volcanoes to Vineyards: Geologic Field Trips through the dynamic landscape of the Pacific Northwest: Geological Society of America Field Guide 15, p. 407-434.

Miller, M.B., 2014, Roadside Geology of Oregon: Mountain Press, Missoula, 386p.

Robinson, P.T., and Stensland, D.H., 1979, Geologic Map of the Smith Rock Area, Jefferson, Deschutes, and Crook Counties, Oregon. US Geological Survey Miscellaneous Investigations Map I-1142. 1:48,000.

Walker, G.W., and MacLeod, 1991, Geologic Map of Oregon. US Geological Survey. 1:500,000.

And some links:
Smith Rock State Park: https://oregonstateparks.org/index.cfm?do=parkPage.dsp_parkPage&parkId=36

Climbing article: https://www.climbing.com/places/thanks-volcanoes-climbing-in-oregon/

Seeing some cool properties of water through the lens of its molecular structure

We all know the importance of water—our bodies are mostly water, we need it to survive, it’s the second most important ingredient in coffee… Geologically, it facilitates almost everything we know, from erosion to magma formation to rock fracture. I’m often struck by how so many of water’s unusual properties are determined by its chemistry and molecular structure –and in a very understandable way.

Waterfalls and cliff, New Zealand.

waterfalls in Fjordland, South Island, New Zealand.

Water molecules are polar
Many of water’s properties stem directly from its polar nature –and its polar nature comes right from its molecular structure. Here’s how. Read more…

Countertop Geology: Desperate for rocks? Visit a “granite” countertop store!

Where can you see some rocks? It’s winter and everything’s covered in snow –or you’re visiting family in some place where there’s virtually no bedrock exposed anywhere –or you’re simply stranded far from any good rocks in the center of a big city.IP18-0957c

Take yourself on a field trip to a granite countertop store! You might not see very much real granite, but you will see some other types: folded gneiss, pegmatite, amphibolite, quartzite, maybe even some granite… and a lot of amazing metamorphic and igneous features and faults –and they’re all polished and none are covered by vegetation.

I needed a rock fix the other day while visiting my mother in SW Florida –so I drove to a granite countertop store. And wow— I saw all sorts of great stuff, a lot of which related to faulting and fracturing, and a lot of it could go right into a geology textbook. In Florida!

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Red garnet along with quartz and feldspar in gneiss -a metamorphic rock.

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Shaping of Landscape: A primer on weathering and erosion

Most of us love landscapes –and many of us find ourselves wondering how they came to look the way they do. In most cases, landscapes take their shape through the combined processes of weathering and erosion. While weathering and erosion constitute entire fields of study unto themselves, this primer outlines some of the basics—which pretty much underlie all the further details of how natural processes shape landscapes.

Incised meanders on the Green River, Utah

Aerial view of incised meanders of Green River, Utah.

Two definitions: weathering describes the in-place breakdown of rock material whereas erosion is the removal of that material. Basically, weathering turns solid rock into crud while erosion allows that crud to move away.

Weathering
Weathering processes fall into two categories: physical and chemical.  Physical weathering consists of the actual breakage of rock; any process that promotes breakage, be it enlargement of cracks, splitting, spalling, or fracturing, is a type of physical weathering.  Common examples include enlargement of cracks through freezing and thawing, enlargement of cracks during root growth, and splitting or spalling of rock from thermal expansion during fires.

Spalling of volcanic rock

Spalling of volcanic rock–likely from thermal expansion during a fire.

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Iceland –where you can walk a mid-Atlantic rift –and some other geology photos

While Iceland hosts an amazing variety of awesome landscapes, what stands out to me most are its incredible exposures of the Mid-Atlantic ridge. To the north and south, the ridge lies beneath some 2500m of water, forming a rift that separates the North American plate from the Eurasian plate. The rift spreads apart at a rate of some 2.5 cm/year, forming new oceanic lithosphere in the process. But in Iceland, you can actually walk around in it!

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Geologic map of Iceland as compiled from references listed below.

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Hug Point State Park, Oregon, USA –sea cliffs expose a Miocene delta invaded by lava flows

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Alcove and tidepool at Hug Point

Imagine, some 15 million years ago, basaltic lava flows pouring down a river valley to the coast –and then somehow invading downwards into the sandy sediments of its delta. Today, you can see evidence for these events in the sea cliffs near Hug Point in Oregon. There, numerous basalt dikes and sills invade awesome sandstone exposures of the Astoria Formation, some of which exhibit highly contorted bedding, likely caused by the invading lava. It’s also really beautiful, with numerous alcoves and small sea caves to explore. And at low to medium-low tides, you can walk miles along the sandy beach!

(Click on any of the images to see them at a larger size)

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Devil’s Punchbowl –Awesome geology on a beautiful Oregon beach

You could teach a geology course at Devil’s Punchbowl, a state park just north of Newport, Oregon. Along this half-mile stretch of beach and rocky tidepools, you see tilted sedimentary rocks, normal faults, an angular unconformity beneath an uplifted marine terrace, invasive lava flows, and of course amazing erosional features typical of Oregon’s spectacular coastline. And every one of these features tells a story. You can click on any of the images below to see them at a larger size.

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View southward from Cape Foulweather to the Devil’s Punchbowl.

 

180629-58ceThe rocks. They’re mostly shallow marine sandstones of the Astoria Formation, deposited in the early part of the Miocene, between about 16.5 to 22 million years ago. The rocks are tilted so you can walk horizontally into younger ones, which tend to be finer grained and more thinly bedded than the rocks below. This change in grain size suggests a gradual deepening of the water level through time. In many places, you can find small deposits of broken clam shells, likely stirred up and scattered during storms –and on the southern edge of the first headland north of the Punchbowl, you can find some spectacular soft-sediment deformation, probably brought on by submarine slumping. Later rock alteration from circulating hot groundwater caused iron sulfide minerals to crystallize within some of the sandstone. Read more…

Grand Canyon Unconformities –and a Cambrian Island

A prominent ledge punctuates the landscape towards the bottom of the Grand Canyon. It’s the Tapeats Sandstone, deposited during the Cambrian Period about 520 million years ago, when the ocean was beginning to encroach on the North American continent, an event called the Cambrian Transgression. Above the ledge, you can see more than 3000 feet of near-horizontal sedimentary rocks, eroded into cliffs and slopes depending on their ability to withstand weathering and erosion. These rocks, deposited during the rest of the Paleozoic Era, are often used to demonstrate the vastness of geologic time–some 300 million years of it.

View of the Grand Canyon from the South Rim trail. Arrows point to the Cambrian Tapeats Sandstone.

View of the Grand Canyon from the South Rim trail. Arrows point to the Tapeats Sandstone.

But the razor-thin surface between the Tapeats and the underlying Proterozoic-age rock reflects the passage of far more geologic time  –about 600 million years where the Tapeats sits on top of the sedimentary rocks of the Grand Canyon Supergroup. Those rocks are easy to spot on the photo above because they contain the bright red rock called the Hakatai Shale. Even more time passed across the surface where the Tapeats sits on top of the 1.7 billion year old metamorphic basement rock. You can put your thumb on the basement and a finger on the Tapeats –and your hand will span 1.2 billion years! Read more…

Sampling New Zealand’s (Amazing) Geology

New Zealand’s landscape can make just about anybody appreciate geology. Its glaciated peaks, its coastline –that ranges from ragged cliffs to sandy beaches to glacial fjords– its active volcanoes… they all work together to shout “Earth Science!” With that in mind, here’s some basics of New Zealand’s amazing geology, followed by some geological highlights of my trip of January and early February, 2018.

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Map of New Zealand, showing accreted terranes in colors and cover assemblage in gray.

North and South Island Bedrock  The different colors on this map show New Zealand’s basement rock, named so because it forms the lowest known bedrock foundation of any given area. The basement tells stories of New Zealand’s deep past, from about 500-100 million years ago. Individual colors signify different terranes, accreted (added) one-by-one through plate motions to the edge of what was then the supercontinent Gondwana. They mostly consist of sedimentary and metamorphosed sedimentary rock, although the narrow belt of purple-colored Dun Mountain Ophiolite formed as oceanic lithosphere, and the red-colored areas consist of granitic igneous rock, some of which has been metamorphosed to gneiss.

Gray indicates the younger cover rock, formed after accretion of the terranes. Consisting of a wide range of sedimentary and volcanic rocks, as well as recently deposited sediment, it’s just as interesting and variable as the terranes. Because it includes volcanoes, it’s largely the cover that gives the North Island its distinctive flair. By contrast, the South Island consists largely of uplifted basement rock, much of which has been –and still is—glaciated. All those long deep lakes, such as Lakes Wanaka and Tekapo, were carved by glaciers and are now floored with their deposits of till.

Andesite stratovolcano, New Zealand

Mt. Ngauruhoe, a 7000 year-old andesite stratocone near Ruapehu on the North Island

Those differences exist largely because the North and South Islands occupy different plate tectonic settings. The North Island sits over a subduction zone, so it hosts an active Read more…

Cove Palisades, Oregon: a tidy short story in the vastness of time

If I were a water skier, I’d go to Lake Billy Chinook at Cove Palisades where I could ski and see amazing geology at the same time. On the other hand, I’d probably keep crashing because the geology is so dramatic! Maybe a canoe would be better.

Lake Billy Chinook, Oregon

View across the Crooked River Arm of Lake Billy Chinook to some of the 1.2 million year old canyon-filling basalt (right) and Deschutes Fm (left). The cliff on the far left of the photo is also part of the 1.2 million year basalt.

The lake itself fills canyons of the Crooked, Deschutes and Metolius Rivers. It backs up behind Round Butte Dam, which blocks the river channel just down from where the rivers merge. The rocks here tell a story of earlier river canyons that occupied the same places as today’s Crooked and Deschutes Rivers. These older canyons were filled by basaltic lava flows that now line some of the walls of today’s canyons.

CovePalisades2From the geologic map, modified from Bishop and Smith, 1990, you can see how the brown-colored canyon-filling basalt, (called the “Intracanyon Basalt”) forms narrow outcrops within today’s Crooked and Deschutes canyon areas. It erupted about 1.2 million years ago and flowed from a vent about 60 miles to the south. You can also see that most of the bedrock (in shades of green) consists of the Deschutes Formation, and that there are a lot of landslides along the canyon sides.

The cross-section at the bottom of the map shows the view along a west-to-east line. Multiple flows of the intracanyon basalt filled the canyon 1.2 million years ago –and since then the river has re-established its channel pretty much in the old canyon. While the map and cross-section views suggest the flows moved down narrow valleys or canyons, you can actually see the canyon edges, several of which are visible right from the road.

Read more…

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