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Archive for the tag “Oregon geology”

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)

HugPointCRBGYou can read more about the Columbia River Basalt Group on an earlier post, but basically, it mostly erupted from fissures in northeastern Oregon and southeastern Washington between 17-6 million years ago (although most activity ended by 14 Ma). They’re called “flood basalts” because they completely flooded the landscape. Many of the flows made it all the way to the Pacific Ocean. They followed the ancient Columbia River and also probably one farther south across today’s Coast Range.

Most researchers now agree that on reaching the coastline, some of these flows somehow invaded the existing sediments, now mostly the Astoria Formation, to form dikes and sills in the rock. In places, they also inflated weak zones to form shallow magma chambers. Some of these magma chambers are preserved as thick sills along the northern coast, such as at Neahkahnie Mountain, while some actually fed undersea volcanoes, such as Haystack Rock at Cannon Beach.

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Basalt sea cliffs at Neahkahnie Mountain

Probably the most accessible exposures of the basalt are in the small headlands immediately north and south of the parking lot. If you go south, look for a pair of dikes as well as a sill of the basalt. Just north of the parking lot, you can’t miss the narrow sill that extends diagonally up from a wave-eroded alcove. Walk around the point to see a much larger intrusion that appears to connect with the sill. One of its sides is faulted and has eroded into a small sea cave.

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Overview of Hug Point area, looking north past Cannon Beach to Ecola Point, Oregon. If you click on this image, you can see it in another window at a much larger size.

Hug Point itself forms the second headland north of the parking area, and it protrudes far enough into the surf that you practically need to “hug” the rocks to get around, hence its name. In the late 1800’s travelers carved a road along the cliff base, which makes passage relatively easy when the tide isn’t too high. Sandstone of the Astoria Formation along this stretch is coarse grained, with mostly quartz and feldspar grains. You can also see abundant cross-bedding from deposition by currents, as well as rip-up clasts, where storms eroded the underlying bed and included parts of it within the newly deposited sand.

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Cross-bedding in Miocene Astoria Formation and road along base of Hug Point. Note the rip-up clasts at the base of the light-colored bed. Also note the barnacles –no passage here at high tide!

This coarse part of the Astoria Formation is called the Angora Peak Member, and was deposited on a delta that was continually affected by waves and storms of the Miocene ocean. The rocks dip gently to the northeast, to indicate younger rocks in that direction.

A cliff of highly contorted sandstone lies Immediately north of Hug Point. The irregular nature of the folding suggests that deformation took place while the Astoria Formation was still soft, hence the term “soft-sediment deformation”. Given the abundance of the basaltic intrusions here, geologists interpret the cause of this folding as related to the intrusions. More effects of the intrusions are the breccias you can see another quarter mile to the north. There, highly fragmented sandstone and basalt are mixed together, a likely product of the explosions that resulted when the lava encountered the water-rich sediment.

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Contorted Astoria Formation in sea cliff.

In another mile, you reach Lion Rock and Humbug Point, where the Astoria Formation shows more interaction with the basalt –and another half mile beyond that, Silver Point. There, a cliff exposes shale of the Astoria Formation’s Silver Point member, deposited in a deeper part of the delta complex. As these rocks sit on top the coarser Angora Peak member, they suggest that the delta was subsiding through time. And if you want to keep walking? Cannon Beach’s Haystack Rock is just another two miles away!

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Haystack Rock at Cannon Beach. The vent area of an undersea volcano fed by lavas of the Columbia River Basalt Group!


For more photos of Hug Point, including a closer view of those weird folds, please visit my website, geologypics.com –and type “hug” into the keyword search. All the images there are freely downloadable for noncommercial, personal or instructional uses.

Here’s the reference for the map of the CRBG: Reidel, S.P., Camp, V.E., Tolan, T.L., Martin, B.S. 2013. The Columbia River flood basalt province: stratigraphy, areal extent, volume, and physical volcanology. In The Columbia River Basalt Province, Geological Society of America Special Paper 497, eds. S.P. Reidel, V.E. Camp, M.E. Ross, J.A. Wolff, B.S. Martin, T.L. Tolan, and R.E. Wells, p. 1-44.

And another really good reference for the invasive basalts: Wells, R.E., Niem, A.R., Evarts, R.C., and Hagstrum, J.T. 2009. The Columbia River Basalt Group—From the gorge to the sea. In Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacific Northwest, Geological Society of America Field Guide 15, eds. J.E. O’Connor, R.J. Dorsey, and I.P. Madin, p. 737-774.

–This vignette is a draft version of an entry for my latest book project: Oregon Rocks! A guide to the geology of the Beaver State. To be published (probably not until 2021) by Mountain Press in Missoula.

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…

Just scratching the surface. A geologic cross-section of Oregon speaks to unimaginable events.

The cross-section below runs from the Cascadia subduction zone across Oregon and into eastern Idaho.  It outlines Oregon’s geologic history, beginning with accretion of terranes, intrusion of granitic “stitching plutons”, and deposition of first North American-derived sedimentary rocks, and ending with High Cascades Volcanic activity and glaciation.

Schematic geologic cross-section across Oregon, from the Cascadia Subduction zone into western Idaho.

Schematic geologic cross-section across Oregon, from the Cascadia Subduction zone into western Idaho.

The cross-section barely scratches the surface of things. Moreover, it boils everything down to a list, which is kind of sterile. But the cross-section also provides a platform for your imagination because each one of these events really happened and reflects an entirely different set of landscapes than what we see today.

Think of the CRBG about 15 million years ago. The basalt flows completely covered the landscape of northern Oregon and southern Washington. Or the Clarno volcanoes –only a part of the green layer called “Clarno/John Day”. They were stratovolcanoes in central Oregon –when the climate was tropical! Or try to wrap your mind around the accreted terranes, some of which, like the Wallowa Terrane, contain fossils from the western Pacific.

To emphasize this point, here’s Crater Lake. Crater Lake formed because Mt. Mazama, one of the Cascades’ stratovolcanoes, erupted about 7700 years ago in an eruption so large and violent that it collapsed in on itself to form a caldera. It’s now a national park, with a whole landscape of its own. And if you visit Crater Lake, you’ll see evidence that Mt. Mazama had its own history –which dates back more than 400,000 years. But Crater Lake and Mt. Mazama make up just a tiny part of the Cascades, which are represented on this diagram by just this tiny area that’s shaped like a mountain.

Crater Lake occupies the caldera of Mt. Mazama, which erupted catastrophically some 7700 years ago.

Crater Lake occupies the caldera of Mt. Mazama, which erupted catastrophically some 7700 years ago.

So the cross-section is kind of sterile and just scratches the surface. But what makes geology so incredible is that we’re always learning new things and digging deeper –and we know we’re just scratching the surface –that there will always —always— be something  to learn.


click here and type “Oregon” into the search for photos of Oregon Geology.
click here for information about the new Roadside Geology of Oregon book.

young and old, close and far

Here’s a photo of the Three Sisters Volcanoes in Oregon –looking northward.  The oldest volcano, North Sister, erupted more than 100,000 years ago and so is considered extinct.  Because no lava has erupted there in so long, erosion has cut deeply into the volcano.  By contrast, South Sister, the closest volcano on the left, most recently erupted only 2000 years ago and is much less eroded.

And then there are the stars –you can see the Big Dipper on the right side of the photo.  The closest star in the Big Dipper is some 68 light years away.

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You can see more photos of Oregon by typing the name “Oregon” into the search function on my website at http://www.marlimillerphoto.com/searchstart.html

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