geologictimepics

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Archive for the category “science”

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…

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)

Read more…

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…

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…

Rocks! –a brief illustrated primer

click on any image to see a larger version

Seems like most people I know like rocks. They bring home unusual rocks from vacations; they admire beautiful facing stones on buildings; they frequently ask “What is this rock”? Considering that the type of rock you’re looking at reflects the processes that caused it to form, some basic rock identification skills can go a long way to understanding our planet!

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Rock (left, igneous-granite) and minerals (right, quartz and kyanite). Notice that the granite is made of a variety of minerals.

Of course there are thousands of different rock types —But! they ALL fit into one of three categories: igneous, sedimentary, or metamorphic. Here’s a brief, illustrated summary of each.

Igneous rocks are those that form by cooling and crystallization from a molten state. Consequently, they consist of crystals of various minerals that form an interlocking mosaic like the rock in the photo to the right. Igneous rocks are further classified as “intrusive” or “extrusive”, depending if they form beneath Earth’s surface (intrusive) or on Earth’s surface (extrusive). Extrusive rocks are more commonly called volcanic rocks. Generally speaking, intrusive rocks are coarsely crystalline whereas volcanic ones are finely crystalline. Check out this gallery of igneous rock photos.

Sedimentary rocks are made of particles (“sediment”) of pre-existing rock that are deposited as layers on Earth’s surface and then become cemented together. Individual layers of sedimentary rock are called “beds”. Bedding is best observed from a distance; most individual sedimentary rocks come from within a bed and so may appear homogeneous. Check out this gallery of sedimentary rock photos.

Metamorphic rocks are pre-existing rocks that change (“metamorphose”) because they are subject to high temperatures and/or pressures. This change involves the growth of new crystals in the rock. Because this growth typically occurs under conditions of high pressure as well as temperature, the new minerals tend to grow in a preferred orientation, leading to a fine-scale layering in the rock. This layering is called foliation. Unlike bedding in sedimentary rock, foliation tends to be irregular and marked by differently colored zones of different minerals. Check out this gallery of metamorphic rock photos.

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Sedimentary (sandstone, L), Igneous (granite, Ctr), and Metamorphic (gneiss, R) specimens

Key

simplified key to recognizing main rock types

Telling Igneous, Sedimentary, and Metamorphic rocks apart is usually pretty easy. First, decide if the rock consists of crystals or rounded grains. If it consists of crystals, then it is igneous or metamorphic; if it consists of grains, then it is sedimentary. If the crystals are arranged into layers or bands, the rock is metamorphic; if they are randomly arranged, then it is igneous. Igneous rocks with large crystals generally indicate slow cooling within the earth (intrusive). Conversely, igneous rocks with small crystals generally indicate rapid cooling on Earth’s surface (volcanic).

Igneous Rock –more details

Intrusive and volcanic rocks are further classified based on their chemistry and texture according to the chart below. This is one place where mineral identification becomes very important because minerals reflect the rock’s chemistry. Importantly, rocks with high silica content, such as rhyolite and granite, typically have fairly low iron contents, and so tend to have minerals that are light in color, such as K-feldspar, sodium-rich plagioclase, and quartz. Conversely, rocks with low silica content, such as basalt and gabbro, typically have high iron contents, and so have minerals that tend to be dark in color.

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Principal igneous rock types. Their classification depends on texture and composition. Fine-grained rocks are extrusive (upper row), whereas coarse-grained rocks are intrusive (lower row). Silica content then determines the specific rock name: gabbro and basalt <50-57%, SiO2; diorite and andesite, 57-67%; granite and rhyolite, 67+%.   Notice that rocks tend to be darker, denser, and more iron rich towards the lower silica end of the spectrum.

More on Volcanic Rock
Being igneous, volcanic rocks are made of crystals –but they’re so fine grained, you often can’t see that without a microscope. Thankfully, many volcanic rocks contain phenocrysts, larger crystals surrounded by the finer grained matrix. If you look closely at the photos of basalt and andesite above, you can see phenocrysts of plagioclase feldspar as the small white things.

Below are more photos, showing a more enlarged view of a rock with phenocrysts. Note how fine grained the surrounding matrix is –you can’t really see anything at all. If you look at the microscopic view though you can see that the whole rock is crystalline, even the super-fine matrix. The point here is that, unless the rock contains glass (see next section), the whole rock is crystalline!

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Porphyritic volcanic rock in hand sample (left) and microscopically (right). Note how microscopic view

Volcanic: Glass
One of the more ubiquitous volcanic products, volcanic glass is just that –glass–so it lacks a crystal structure. Glass can form when the lava is so dry as to inhibit crystal growth, as in obsidian, or when lava cools so quickly as to prevent crystal growth, such as with volcanic ash and pumice.

The photos below show pumice, which is frothy volcanic glass. It gets that texture because it forms during violent eruptions –explosively expanding gases in the lava shatter the fast-cooling material so that the rock consists of air bubbles (called vesicles) separated by glassy sidewalls.

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Pumice: frothy volcanic glass from instantaneous cooling. Left-hand image shows close-up view of glass threads. Paper clip for scale.

Volcanic: Pyroclastic Material and Rocks
Pyroclastic materials (also called “tephra”) form during explosive eruptions and so consist of rock fragments and glass ejected violently from the volcano. We classify it according to its size: large fragments are called blocks or bombs; small particles, between about 2mm – 64mm, are called “lapilli”; tiny particles, smaller than 2mm, are called “ash“.  Pumice is also pyroclastic, but it’s considered its own rock type –and it can be of any size. Pyroclastic falls can result from any explosive eruption in which pyroclastic materials fall out from the atmosphere; pyroclastic flows are those that flow out over the ground surface.

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Most tuff contains fragments of pumice in a matrix of ash

Now the rocks. The most common pyroclastic rock is undoubtedly “tuff”, which is composed largely of ash and pumice fragments, erupted mostly during rhyolitic eruptions. Air fall tuff forms from ash that accumulates in layers as it settles from the atmosphere; Ash flow tuff forms from bodies of ash that flow rapidly along the ground, typically incinerating everything in their paths. Because the material flows, it typically does not form layers. Many ash flow tuffs are welded (called “welded tuff”) because of the high temperatures. These highly welded tuffs are sometimes called “ignimbrites”. To identify tuff, look for pieces of pumice floating around in the ashy matrix.

Below’s a view of the Bandelier Tuff in northern New Mexico. It’s a series of ash flow tuffs formed during huge eruptions 1.6 and 1.25 million years ago in the Jemez Mountains. These eruptions formed the Valles-Toledo Caldera (generally just called the “Valles Caldera”). You can get an idea as to the size of the eruptions based on the size of the flows: they’re thick!

Bandelier Tuff, Los Alamos, New Mexico

Cliffs of Bandelier Tuff, erupted from Valles Caldera, New Mexico.

New Zealand’s Taupo Volcanic Zone hosts the most frequent recent rhyolitic eruptions than anywhere else in the world, all active in the last 2 million years. The most recent big eruptions, 26,500 and 1800 years ago, were centered on Lake Taupo, near the middle of the North Island. Below is a map showing the distribution of airfall and ignimbrite (welded ash flow) deposits formed during the eruption at AD 186, just over 1800 years ago. The estimated volume of all eruptive products during this eruption exceeds 105 km3 (Wilson, and Walker, 1985). By comparison, the older “Oruanui” eruption, 26,500 years ago? It likely erupted more than 1000 km3! (Wilson, 2001).

Taupo deposits

Taupo vent (red triangle) and distribution of airfall and ashflow deposits from AD186 eruption.  Inset shows Taupo Volcanic Zone on New Zealand’s North Island. From Wilson and Walker, 1985.

references for Taupo eruptions:
Wilson, C.J.N., and Walker, G.P.L., 1985, The Taupo eruption, New Zealand i. General Aspects, Philosophical Transactions of the Royal Society of London, v. 314, p. 199-228.

Wilson, C.J.N., 2001, The 26.5 Oruanui eruption, New Zealand: an introduction and overview, Journal of Volcanology and Geothermal Research, v. 112, p. 133-174).

Sedimentary Rock –More details

Sedimentary rock may be clastic, biogenic, or chemical, depending on how the particles formed. Clastic sedimentary rocks contain actual pieces of the pre-existing rock that have been transported from the original source. During this transportation, the particle breaks into smaller grains and typically becomes rounded. Clastic sedimentary rocks are further classified according to grain size: shale contains clay-sized grains; siltstone contains silt-sized grains; sandstone contains sand-sized grains; conglomerate contains grains that are pebble to boulder-sized.

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Clastic sedimentary rocks: shale (left), sandstone (center), and conglomerate (right).

Biogenic sedimentary rocks are those that form through biological activity. By far the most common example is limestone, which forms by the production of calcium carbonate by algae and invertebrate animals for shells.   Other examples include dolomite, which forms by the same process as limestone, and chert, which forms by the accumulation of silica-producing organisms on the sea floor.

Chemical sedimentary rocks form by non-biologically induced precipation of minerals. Examples include sinter and travertine, which consist of silica and calcium carbonate respectively, precipitated from hot water at thermal springs. Another important example is bedded salt, which forms today by evaporation in closed desert basins.

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Tilted sedimentary rocks –started out horizontally.

You can’t see the bedding in the rock samples shown above, but if you were to stand back from an outcrop of sedimentary rocks, you probably could see the bedding. That’s because most individual samples don’t go across bedding but instead come from individual beds.

 

 

Metamorphic Rock –more details

Most metamorphic rocks are classified according to their grain size and the resulting nature of their foliation. Slates are the finest grained metamorphic rock, followed by phyllite, schist, and gneiss, being the coarsest grained. Gneiss is especially distinctive because most of its crystals are readily visible and its foliation is marked by bands of different minerals. In general, crystal size corresponds to the metamorphic grade, or intensity, with the most coarsely crystalline rocks being of the highest grades.

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Metamorphic rocks. From left to right: slate, phyllite, schist, gneiss. Note that each rock has layering (foliation) that is caused by a parallel arrangement of platy minerals within the rock.

And then there are metamorphic rocks that form just because of high temperatures, typically because they were heated by the intrusion of a nearby igneous body. This type of metamorphism, called “contact metamorphism” is a common origin for non-foliated marbles and quartzites. Marble forms by contact metamorphism of limestone and dolomite; quartzite forms by contact metamorphism of sandstone.

The photo on the below shows the igneous rock diorite intruding the sedimentary Helena Dolomite in Glacier National Park, Montana. You can see how contact metamorphism has turned the dolomite next to the intrusion into a white marble. Ooooh!

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Intrusive “sill” of diorite and the resulting contact metamorphism of adjacent gray dolomite to white marble in Glacier National Park, MT.


For more, higher resolution photos of each feature or rock type, try doing a geology keyword search for any of the rock types or features described here. Some useful keywords are “igneous, intrusive, volcanic, metamorphic, sedimentary, phenocryst, tuff, pumice, or volcanic glass” –or any others you can think of. Enjoy!

 

Geologypics.com– A new (and free) resource for geological photographs

What better way to kick off my new website than to write about it on my blog? To see it, you just need to click on the word “home” in the space above. Or you can click the link: geologypics.com.

Here’s part of the front page:
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As it says, the site offers free downloads for instructors –and for anybody who’s craving a good geology photograph. It’s my way of contributing to geology education –showing off some of our landscape’s amazing stories and providing resources for other folks who want to do the same.

I think the best part of the whole site is that red button in the middle of the home page. It says “Image Search by Keyword”.

Right now, there are more than 2200 images you can search for — all of which are downloadable at resolutions that generally work for powerpoint. If you search for “sea stack” for example, you’ll get 38 hits –and the page will look like this:

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First page of sea stacks when you search on the term.

 

Notice that ALL the photos are presented as squares–which works for most photos, but not all. To help mitigate that, the photos with vertical or panorama formats say so in their title, so you know to click on them to see the whole image. Take the photo in the upper center, for example –it’s got a  vertical format. Here it is:vertial image

 

A more detailed caption below the photo, along with its ID number appears at the bottom of the pic. This particular image is the chapter opener to the Coast Range in my new book “Roadside Geology of Washington“, which I wrote with Darrel Cowan of University of Washington.

There are also galleries –a chance to browse a variety of images without having to think of keywords. Similar to the search, they’re presented as squares so you need to click on the photo to see the whole thing.

 

Here’s what the photo gallery page looks like (on the left), followed by part of the “glaciation” page you’d see if you clicked on “glaciation”.  Woohoo!

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part of Galleries page (left) and part of Glacial page (right)

 

Then there’s the “About” page, which gives some information about me and details my policies regarding use of the images (basically, you can download freely for your personal, non-commercial use if you give me credit; if you want to use the image in a commercial publication you need to contact me to negotiate fees). There’s also a “News” page, that gives updates on the website. There’s a contact page from which you can send me emails. And the blog? It goes right back to here!

And finally, if you’re looking for a great web designer? Try Kathleen Istudor at Wildwood SEO –she created the site and spent hours coaching me on how to manage it.

Enjoy the site!

 

Science got it right… Maybe we can now accept the reality of climate change?

Along with a zillion other people in the US, I witnessed the total solar eclipse today. Yes, it was amazing and yes, I feel somewhat addicted. The quality of light just before totality was something I’d never before experienced –and the sun’s flash just as it reappeared was something I’ll never forget.  Apparently the next one will be in South America on July 2, 2019–and the next one in the US will be April 8, 2024. Oooh!

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Sun’s corona as seen during the total solar eclipse, August 21, 2017 from Salem, Oregon.

Amazing that us humans can accurately predict these phenomena –to the exact place and time –to the second. Seems like our predictions work! These predictions, of course, are grounded in the physical sciences.

At the same time, many people insist that scientists are mistaken or misguided when they predict global climate change.  I wonder if any of those people saw the eclipse. If so, they might want to reflect on their contradiction.

That’s all.

Glacier in retreat, Athabasca Glacier, Alberta, Canada (120713-65).

This monument marks the position of the front of the Athabasca Glacier of Alberta, Canada in the year 2000. Photo taken in 2012.

Washington’s waterfalls–behind each one is a rock!

Of all the many reasons why waterfalls are great, here’s another: they expose bedrock! And that bedrock tells a story extending back in time long long before the waterfall. This posting describes 9 waterfalls that together paint a partial picture of Washington’s geologic history. The photos and diagrams will all appear in my forthcoming book Roadside Geology of Washington (Mountain Press) that I wrote with Darrel Cowan of the University of Washington.

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Rainbow falls along WA 6 in the Coast Range

 

And waterfalls in heavily forested areas are especially great because they may give the only view of bedrock for miles around! Take Rainbow Falls, for example–the small waterfall on the left. It’s in Washington’s Coast Range along State Highway 6–a place where a roadside geologist could otherwise fall into total despair for lack of good rock exposure. But this beautiful waterfall exposes a lava flow of the Grande Ronde Basalt, which belongs to the Columbia River Basalt Group. Significant? Yes!

This lava erupted in southeastern Washington and northeastern Oregon between about 16 and 15.6 million years ago and completely flooded the landscape of northern Oregon and southern Washington. We know how extensive these flows are because we can see them–and they cover the whole region. The photo below shows them at Palouse Falls in the eastern part of Washington. Take a look at my earlier blog post about the Columbia River Basalt Group? (includes 15 photos and a map).

Read more…

Oregon’s rocky headlands: geologic recycling through erosion and uplift and erosion…

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Crashing waves at Heceta Head, Oregon

You can’t avoid thinking about erosion while standing on one of Oregon’s rocky headlands. The waves keep coming, one after another, each crashing repeatedly against the same rock. Impossibly, the rock appears unmoved and unchanged. How can it not erode?

The answer, of course, is that headlands do erode, quickly, but on a geologic time scale. We just miss out because we live on the much shorter human time scale. And the erosion belongs to a cycle in which coastal uplift causes eroded and flattened headlands to rise and become headlands once again, all subject to more ongoing erosion and uplift.

Wave energy is most intense at headlands because the incoming wave typically feels the ocean bottom near the headland first, which causes the wave to refract. As shown in the aerial photo below, this refraction focuses the wave energy on the headland.

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Wave refraction causes wave energy to focus on the headland. Arrows are perpendicular to wave fronts.

As you can see in the next few images, headlands don’t erode evenly. They erode irregularly, as the waves exploit any kind of weakness in the rocks such as faults and fractures, or if they’re sedimentary, bedding surfaces. The products of this erosion are as beautiful as they are interesting: sea stacks, sea arches, sea caves… The list goes on and on.

Headland and lighthouse, Heceta Head, Oregon

Aerial view of Heceta Head, Oregon.

From the above photo, you can see that sea stacks are simply the leftover remains of a headland as it retreats from erosion. That’s a critical point, because some sea stacks, especially the one with the arch in the photo below, are a long way from today’s coastline.

Sea stacks and sea arch, southern Oregon

Sea stacks and sea arch, southern Oregon

Those rocks, 1/4 to a 1/2 mile away used to be a part of the coastline? The land used to be way out there? YES!!! For me, that’s one of the very coolest things about sea stacks –they so demonstrate the constant change taking place through erosion.

Taken to its extreme, erosion renders headlands into wave-cut platforms, such as the one below at Sunset Bay. Being in the intertidal zone, these platforms make great places for tide-pooling–and ironically, for people-watching too. Geologically, they form important markers because they’re both flat and form at sea level. When found at higher elevations, they indicate uplift.

Wave-cut bench, Sunset Bay, Oregon

Wave-cut bench at Sunset Bay, Oregon

In fact, looking carefully at the photo above, you can see a flat surface on the other side of the bay. It’s an uplifted wave-cut platform! Called a marine terrace, it’s covered by gravel and sand originally deposited in the intertidal zone. Those deposits rest on bedrock that, at an earlier time, was also flattened by the waves. The photo below shows a better view of this terrace from the other side.

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Breaking wave at Shore Acres State Park, Oregon. Tree-covered flat surface in the background is an uplifted marine terrace.

These uplifted marine terraces can be found up and down Oregon’s coastline. Researchers recognize several different levels, the oldest being those uplifted to highest elevations. The one in the photo above at Shore Acres State Park is called the Whiskey Run Terrace and formed about 80,000 years ago. You can see a similar-aged terrace below as the flat surface beneath the lighthouse at Cape Blanco, Oregon’s westernmost point. An older, higher terrace forms the grass-covered flat area on the right side of the photo.

Cape Blanco, Oregon

Cape Blanco, Oregon looking NE. The flat surface beneath the lighthouse is the ~80,000 year-old Cape Blanco Terrace, probably equivalent to the Whiskey Run Terrace at Shore Acres; the flat area on the right side of the photo is the higher Pioneer Terrace,  formed ~105,000 years ago.

Researchers take the approximate ages of the terraces and their elevations to calculate approximate rates of uplift. In this area, Kelsey (1990) estimated a rate of between 4-12 inches of uplift every 1000 years. That might seem slow, but over hundreds of thousands of years, it can accomplish a great deal.

And look! The uplifted terraces? They’re on headlands! Of course, because they’ve been uplifted! And the headlands are now eroding into sea stacks and then platforms –to be uplifted in the future and preserved as marine terraces that sit on top headlands. And on and on, as long as the coastline continues rising.

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Blowhole near Yachats, Oregon. Incoming wave funnels up a channel eroded along a fracture and explodes upwards on reaching the end.

Some links and references:
Kelsey, H.M., 1990, Late Quaternary deformation of marine terraces of the Cascadia Subduction Zone near Cape Blanco, Oregon: Tectonics, v. 9, p. 983-1014. (Detailed study of Cape Blanco, including uplift rates).

Miller, M., 2014, Roadside Geology of Oregon, Mountain Press, Missoula, 386p. (General reference which details the concepts and includes several of the photos used here).

Earth Science Photographs–free downloads for Instructors or anybody: my webpage!

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