geologictimepics

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Archive for the category “volcanoes”

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.

Probably the best place to see a canyon edge is where you enter the park from the east and start down the grade into the Crooked River Canyon. That area’s shown in the white box in the cut-out of the lead photo (below).

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cut-out photo showing locations described in text

There, you can see canyon-filling basalt flows cutting down through the bedding in the older rock. Their contact marks the walls of the old canyon. In my opinion, the best place to photograph this spot is from the road directly below—at the little star on the lead photo. There’s even a waterfall!

Buttress Unconformity, Oregon (Pan)

View upwards to preserved canyon edge, where the intracanyon basalt cuts down through the Deschutes Fm. Location marked by star in previous photo.

The photo below shows another view of a canyon edge—on the west side of the Deschutes River Canyon. It tells pretty much the same story, except that researchers have determined the lava came from downriver. According to Bishop and Smith (1990), some of the basalt, flowing down the Crooked River Canyon, encountered an obstacle somewhere beyond its confluence with the Deschutes River. This obstacle caused the flowing lava to pond and flow back up the Deschutes River Canyon!

Buttress Unconformity, Oregon (Pan)

Intracanyon basalt on skyline cutting down through older Deschutes Fm.

 

The Deschutes Formation. The rock of the original canyons, shown as the well-bedded material in the photos above, belongs to the Deschutes Formation. It formed as deposits from the early High Cascade volcanoes between 7.5 – 4 million years ago. Altogether, the formation exceeds 2000 feet in thickness. At Cove Palisades, the Deschutes Formation beautifully displays nearly its whole range of features, including braided channels, ash fall deposits, sandy debris flows, welded ash flow tuffs, and basaltic lava flows. It even hosts a small shield volcano, shown on the map as Round Mountain. Most of these features appear in the quarter-mile continuous exposure along the grade into the Crooked River Canyon –located by the pink-colored box on the photo above.

Volcaniclastic rock, Oregon

Deschutes Fm. as exposed near upper end of roadcut along eastern grade into canyon

 

Here’s one part of that roadcut—across from the large pullout near the top of the grade. You can see cross-bedded gravel filling scours and channels in underlying volcanic-rich sandstone and tuff. In the background, the shaded cliff and flat area is made of a basalt flow. It forms the rimrock of the Crooked River Canyon. The next photo shows this basalt, with some wonderful colonnade, at the very top of the grade.

Columnar-jointed basalt, Oregon

Colonnade in basalt of Deschutes Fm. The roadway makes the gray band at the bottom.

Then there’s “The Ship” –a beautifully exposed outcrop of ash flow tuff called the “Cove Ignimbrite”. This tuff, which is also exposed along the long roadcut, points to a period of unusually explosive volcanic activity in the early High Cascades. It turns out there are 13 other ash flow tuffs preserved in the Deschutes Formation. They’re described by Pitcher and others (2017) who found that they all erupted between about 6.25 and 4.45 million years ago.

Ash Flow tuff, Oregon

Cove Ignimbrite at “The Ship”

And Geologic Time  We see evidence of early canyons, carved into the Deschutes Formation by weathering and erosion. Later, these canyons filled with basaltic lava flows that erupted some 60 miles to the south near today’s Newberry Volcano. Weathering and erosion continued its work and carved the canyons again. But that’s not all. Landslides speak to weathering and erosion that continues today in the canyon. The Deschutes Formation, which formed the original canyon walls, is much older than all of this –it’s made of more than 2000 feet of material from volcanoes that no longer exist! Among other things, it tells us of an especially explosive period in the history of these former volcanoes. All within 7.5 million years.

Most geologists (me included) tend to think of 7.5 million years as a pretty short time. After all, the Cenozoic Era started about 66 million years ago –and before that was another 4,484 million years of Earth history. When you dig into the details though, you come to appreciate just how long that 7.5 million years really is –and then the vastness of geologic time becomes almost overwhelming.


You can view and download any of these images–and others from Cove Palisades– at a resolution that works for power point by typing “Cove Palisades” into the keyword search at geologypics.com.


References:
Bishop, E.M., and Smith, G.A., 1990, A field guide to the geology of Cove Palisades State Park and the Deschutes Basin in central Oregon: Oregon Geology, v. 52, p. 3-16.

Pitcher, B.W., Kent, A.J.R., Grunder, A.L., and Duncan, R.A., 2017, Frequency and volumes of ignimbrite eruptions following the Late Neogene initiation of the Central Oregon High Cascades: Journal of Volcanology and Geothermal Research, v. 329, p. 1-22.

 

 

 

 

 

 

 

 

Mauna Loa Volcano, Hawai’i –Earth’s largest active volcano

To get an idea of the immensity of Mauna Loa Volcano, take a look at the photo below. That rounded shape continues from its summit area at 13,678 feet above sea level to about 18,000 feet below sea level –and then another 25,000 feet or so below that because the mountain has sunk into the oceanic crust. It’s unquestionably the world’s largest active volcano.

Mauna Loa Shield Volcano

Profile of Mauna Loa Shield Volcano from… Mauna Loa Shield Volcano! (Geologypics: (170919s-15))

Briefly, Mauna Loa’s made of basalt. Basaltic lava flows, being comparatively low in silica, have low viscosities and so cannot maintain steep slopes, resulting in broad, relatively low gradient volcanoes called shields. With just a little imagination, you can see how Mauna Loa’s shape resembles that back side of some shield one of King Arthur’s Knights might carry into battle.

Read more…

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:
home3

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:

Sea Stack search

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!

galleries

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!

 

Summarizing Washington State’s Geology –in 19 photo out-takes

Washington State displays such an incredible array of geologic processes and features that it makes me gasp –which is one reason why writing “Roadside Geology of Washington” was such a wonderful experience. I also got to do it with my long-time friend and colleague (and former thesis advisor at the University of Washington) Darrel Cowan. The book should be on bookshelves in mid-September –and I can’t think of a better way to celebrate than by summarizing Washington’s amazing geology with a bunch of out-take photos –ones that didn’t made it into the book or even to my editor. Like the photo below:

Mount Baker, Washington (150916-4)

Mt. Baker, a glaciated stratovolcano in northern Washington State.

Mount Baker’s a stratovolcano that erupted its way through the metamorphic rock of the North Cascades. I took the photo from the parking lot at a spot called Artist’s Point –at the end of WA 542 –and my editor nixed it because I already had enough snow-capped volcanoes in the book.

On the cross-section below–which includes elements of Oregon as well as Washington, Mt. Baker is represented by the pink volcano-shaped thing labelled “High Cascades”. The following 15 or so photos illustrate most of the other features on the cross-section –so together, they illustrate much of the geology and geologic history of the state!

Cross-section across PNW

Generalized cross-section across Washington and Oregon.

Washington State and geologic provinces

Washington State and geologic provinces.

A quick note about organization: I’m separating the images according to their  physiographic province. There are six in Washington: Coast Range, Puget Lowland, North Cascades, South Cascades, Okanogan Highlands, and Columbia Basin.

 

Coast Range:
As you can see in the cross-section, the Coast Range borders the Cascadia Subduction Zone and consists of three main elements: the Hoh Accretion Assemblage in yellow, Siletzia (called the “Crescent Formation” in Washington) in purple, and the post-accretion sedimentary rock in brown. Siletzia is the oldest. It was thrust over the Hoh Accretion Assemblage, which is still being accreted at the subduction zone. The post-Accretion sedimentary rocks were deposited over the top of Siletzia after it was accreted about 50 million years ago.

And here are some photos! Siletzia formed as an oceanic plateau and so is characterized Read more…

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…

Columbia River Basalt Group–outrageous!

I can’t stop thinking about the Columbia River Basalt Group–the series of basalt flows that blanketed so much of my state of Oregon about 15 million years ago. Abbreviated as “CRBG”, it covers a lot of Washington too, as well as parts of western Idaho and northern Nevada. If you’re driving across those parts, you’ll likely travel miles and miles and miles over basalt basalt basalt –and that causes some people to say (mistakenly) that it’s boring. Some geologists even get grumpy about it because it covers up all the older rock.  Outrageous!

Lava flows of the CRBG in northern Oregon and Mt. Adams of southern Washington.  With views like this, how can you say the CRBG is boring? (Location "F" on map below.)

Lava flows of the CRBG in northern Oregon and Mt. Adams of southern Washington. With views like this, how can you say the CRBG is boring? (Photo “F” on map below.)

But of course, the CRBG is outrageous for a whole host of other reasons. For one thing, it really is huge: it covers an area of more than 77,000 square miles with a volume of more than 52,000 cubic miles –that’s more than 50x the volume of air between the north and south rims of the Grand Canyon! Really—the National Park Service estimated the volume of “Grand Canyon Air” to be about 1,000 cubic miles. It also erupted over a fairly short period of time: from about 17 million years ago to 6 million –but 96% of it erupted between 17 and 14.5 million years ago.

CRBGblog

And… most of it erupted from fissures in eastern Oregon and Washington –the roots of which are now preserved as dikes. And… many of the lavas made it all the way to the Pacific Ocean. And… (here’s the outrageous part), on reaching the Pacific, many of the flows re-intruded into the existing sediments and sedimentary rocks along the coastline to form their own magma chambers, some of which were thousands of feet thick! AND… some basaltic magma from those chambers then re-intruded the country rock to form dikes –and some even re-erupted on the seafloor!

All these outrageous details. Now think about them for a moment. They really happened. That’s what I find so wonderful and amazing about geology. We learn all these things and we put them in some part of our consciousness that doesn’t really let them soak in –but once in awhile they do.

Finally, the CRBG is beautiful and forms beautiful landscapes! Below are some photos to illustrate it, from feeder dikes in eastern Oregon to sea stacks eroded from a giant sill on the coast.

And I’ll save my snarky comments about young earth creationism for another post.

–and at the bottom, I’m adding a short glossary to explain some of the terms.

Ok… the photos!

 

Photo A. Steens Mountain and Alvord Desert.  The CRBG started with eruption of the Steens Basalt about 16.7 million years ago, which makes up the upper 3000′ or so of Steens Mountain, shown here.  Steens Mountain is one of our state treasures –it’s a fault-block mountain, uplifted by Basin-Range extension along a normal fault along its eastern side.

Fault-bounded east front of Steens Mountain and Alvord Desert.

Fault-bounded east front of Steens Mountain; mudcracked playa of Alvord Desert in foreground.

 

Photo B. Steens Basalt at Abert Rim. Like most of the CRBG, The Steens basalt covered outrageously huge areas.  It also makes up the cliffs above Lake Abert about 75 miles to the east.  Called Abert Rim, the cliffs are also uplifted by a big normal fault.  Lake Abert occupies the downdropped basin.  And much of the Steens basalt consists of this really distinctive porphyry with outrageously big plagioclase crystals!

Photo B.  Steens Basalt at Lake Abert; Abert Rim in background.

Photo B. Steens Basalt at Lake Abert; Abert Rim in background.

 

Photos C-1, C-2. CRBG dikes.  One reason we know that the CRBG erupted from fissures is that we can see their roots, as dikes cutting through older rock.  C-1 shows a dike cutting through previously erupted basalt flows in Grande Ronde Canyon, Washington; C-2 shows some narrow little dikes cutting accreted rock of the Triassic Martin Bridge Limestone. Photos 5 and 6 of my last post shows some aerial photos and describes this area in more detail.C. Feeder dikes

 

Photo D. Imnaha Canyon. The next major unit of the CRBG is the Imnaha Basalt, followed by the Grande Ronde Basalt.  Both these units erupted from sites in northeastern Oregon and southeastern Washington.  This view of Imnaha Canyon in Oregon shows the Imnaha Basalt near the bottom and the Grande Ronde Basalt at the top.

Photo D.  Imnaha Canyon, Oregon.

Photo D. Imnaha Canyon, Oregon.

 

Photo E. Picture Gorge Basalt at the Painted Hills.  And the next youngest unit of the CRBG was the Picture Gorge Basalt, shown capping the ridge in the background. Unlike most of the CRBG, the Picture Gorge Basalt originated in central Oregon, not too far from here–there’s a whole swarm of dikes near the town of Monument, Oregon.

The colorful hills in the foreground make up the Painted Hills of John Day Fossil Beds National Monument, another of our state treasures.  I like this photo because it gives a sense of what lies beneath the CRBG –and the John Day Fossil Beds are outrageous in their own way–but save that for another time.

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Photo F. Lava Flows of the CRBG and Mt. Adams, a modern volcano of the High Cascades in Washington.  See the first picture at the top of the post!

 

Photo G. Wanapum Basalt near The Dalles. This exposure of the Wanapum Basalt, which overlies the Picture Gorge Basalt, tells the story of the CRBG as it flowed into and filled a lake along the Columbia River some 15 million years ago. At the bottom of the flow, pillow basalt formed as the lava poured into the lake, while the upper part of the flow shows the columnar jointing typical of basalt that flows across land.  What’s more, this exposure lies less than a mile off I-84 in The Dalles, Oregon.  See page 251 of the new Roadside Geology of Oregon for another photo and more description!

Photo G. Single flow of Wanapum Basalt near The Dalles, Oregon.

Photo G. Single flow of Wanapum Basalt near The Dalles, Oregon.

 

Photo H.  Upper North Falls, Silver Falls State Park, Oregon.  This wonderful state park hosts about a zillion waterfalls that spill over cliffs of CRBG, 14 of which lie in the main river channels of the north and south forks of Silver Creek.  The falls depicted in this photo are 136 feet high!

Upper North Falls at Silver Falls State Park, OR.  The roof of the alcove consists of Wanapum Basalt, the bedrock near the river channel consists of Grande Ronde Basalt.

Upper North Falls at Silver Falls State Park. The roof of the alcove consists of Wanapum Basalt, the bedrock near the river consists of Grande Ronde Basalt.

Notice that the picture’s taken from behind the water. The trail goes into a big alcove, so it’s easy and safe.  The alcove formed because this particular waterfall crosses the contact between the Wanapum Basalt and the underlying Grande Ronde Basalt –and there is a 10-20′ thick, easily eroded, sedimentary unit between the two.  Remember the Grande Ronde Basalt –from Photo D in northeastern Oregon? Here it is, just east of Salem!

 

Photo I.  Saddle Mountain, northern Coast Range.  Here starts the truly outrageous part of the CRBG story.  Saddle Mountain, the highest point in the northern Coast Ranges, consists almost entirely of the rock on the right: brecciated pillow basalt, full of the alteration mineral palagonite. Apparently, the basalt started to flow into the ocean at about here, formed pillows and fragmented like crazy in the water-lava explosions. I. Saddle Mtn

But!  These flows were likely confined too –such as in a submarine canyon–which allowed them to develop enough of a pressure gradient to intrude downward into bedding surfaces, faults, and fractures of the Astoria Formation.  The diagram below illustrates the process in cross-section.  The diagram also give a context for photos I-L.  intrusive CRBG diagram4

 

Photo J.  Sea stacks of intrusive Columbia River Basalt Group at Ecola State Park.  Some of the magma chambers were several thousand feet thick and are now exposed as gigantic sills along the coast.  One such sill is Tillamook Head, of which Ecola State Park is a part –and it’s eroding into the sea stacks you can see in the distance.J.130120-11lrs

 

Photo K.  Haystack Rock at Cannon Beach, OR.  Go figure, one of our iconic state landmarks is an undersea volcano?  You can actually walk out to this thing at low tide and see lots of pillow basalt and dikes intruding the Astoria Formation.  The smaller sea stacks are part of the same complex.K.130121-12

 

Photo L. Seal Rock, Oregon.  Seal Rock is the southernmost exposure of CRBG on the coast –and it too, is intrusive.  It’s a big dike that trends NNW for about a quarter mile out to sea.  And along its edges, there are smaller dikes that you can see intruding the Astoria Formation, such as in the smaller photo.  The arrow points to where you can see the small intrusion, at low to medium tides.

L. Seal Rock


Some Terms:
dike: a tabular-shaped intrusion that cuts across layering in the surrounding rock.  Imagine magma flowing along a crack and eventually cooling down and crystallizing.  That would form a dike.  A feeder dike is a dike that fed lava flows at the surface.

normal fault: a type of fault along which younger rocks from above slide down against older rocks below.  They typically form when the crust is being extended.

porphyry: an igneous rock with larger, easily visible crystals floating around in a matrix of much smaller ones.

sill: an intrusion that runs parallel to layering in the surrounding rock.


 

Some references:

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.

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.


Some links:

Roadside Geology of Oregon
Geology pictures for free download
Geologic map of Oregon

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.

Crater Lake caldera, Oregon –some things happen quickly!

Crater Lake never ceases to amaze me.  It’s huge –some 6 miles (10 km) across, deep –some 1700 feet deep in parts –the deepest lake in the United States and 7th deepest on the planet– incredibly clear, and really really blue.  And for volcano buffs, one of the best places ever!

Crater Lake as seen from The Watchman.  Wizard Island, which formed after the caldera collapse, occupies the center of the photo.

Crater Lake as seen from The Watchman. Wizard Island, which formed after the caldera collapse, occupies the center of the photo.

Crater Lake is a caldera, formed when ancient Mt. Mazama erupted so catastrophically that it emptied its magma chamber sufficiently for the overlying part of the mountain to collapse downward into the empty space.  That was about 7700 years ago.  Soon afterwards, Wizard Island formed, along with some other volcanic features that are now hidden beneath the lake–and then over the years, the lake filled to its present depth.  It’s unlikely to rise any higher because there is a permeable zone of rock at lake level that acts as a drain.

Here’s one of the coolest things about the cataclysmic eruption: Not only was it really big, but it happened really fast.  We know it was big because we can see pumice, exploded out of the volcano, blanketing the landscape for 100s of square miles to the north of the volcano –and we can see the caldera.  We can tell it happened quickly because the base of the pumice is welded onto a rhyolite flow that erupted at the beginning stages of the collapse; the rhyolite was still HOT when the pumice landed on it!  You can see the welded pumice on top the Cleetwood Flow along the road at Cleetwood Cove.

pumice welded onto top of Cleetwood rhyolite flow at Cleetwood Cove.  Note how the base of the pumice is red from oxidation --and forms a ledge because it's so hard.

pumice welded onto top of Cleetwood rhyolite flow at Cleetwood Cove. Note how the base of the pumice is red from oxidation –and forms a ledge because it’s so hard.  Pumice blankets the landscape all around Crater Lake.

Crater Lake though, is so much more than a caldera –it’s the exposed inside of a big stratovolcano!  Where else can you see, exposed in beautiful natural cross-sections, lava flow after lava flow, each of which erupted long before the caldera collapse and built the original volcano? Within the caldera itself, these flows go back 400,000 years–the oldest ones being those that make up Phantom Ship –the cool little island (some 50′ tall) in Crater Lake’s southeast corner.

Phantom Ship, in Crater Lake's southeast corner, is made of the caldera's oldest known rock, at 400,000 years old.

Phantom Ship, in Crater Lake’s southeast corner, is made of the caldera’s oldest known rock, at 400,000 years old.

I can’t resist.  The caldera formed about 7700 years ago, incredibly recent in Earth history–incredibly recent in just the history of Mt. Mazama!  To a young earth creationist though, that’s 1700 years before Earth formed.  Now THAT’S amazing!


Click here if you want to see a Geologic map of Crater Lake.
Or… for more pictures of Crater Lake, type its name into the Geology Search Engine.  Or… check out the new Roadside Geology of Oregon book!

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