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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.

Here are a few more numbers. The mountain covers an area of 1900 square miles (5100 km3) of land and has a volume of 18,000 cubic miles (75,000 km3). 18,000 cubic miles??? That’s 18x the volume of air estimated by the National Park Service that’s between the rims in the Grand Canyon!

Considering that Mauna Loa’s oldest lavas (deep beneath the seafloor) are no older than 1 million years old and probably much younger –that’s a lot of lava in a geologically short period of time. And we’re experiencing its growth today –the volcano last erupted in 1984 –and 32 times before that since 1843.

To gain more appreciation for this huge mountain, look at this geologic map of Hawaii, made by the USGS in 2007.

Hawaii Geo

2007 USGS Geologic Map of Hawai’i. Lavas from Mauna Loa, cover half the island.

Mauna Loa volcano, outlined in white, covers half the Big Island of Hawai’i. From the map, you can also see that many of its lavas erupted from the summit area, now a caldera –and that most of the other lavas came from fissures along the volcano’s southwestern and northeastern flanks. If you click on the map, you can see it in a larger view.

Note that the red-colored area, lavas from Kilauea, make up the southeastern coast. That’s where most of the eruptive activity is now, but Mauna Loa’s not at all finished.

 

September, 2017 -hiking the volcano

This September, I spent 4 days backpacking up Mauna Loa’s northeastern flank to its summit –and I got to do it with my daughter Lindsay and her friend Morgan. What an incredible trip –41 miles of young lava in 4 days.

What follows are photos and descriptions of some of Mauna Loa’s amazing features. For starters, it was beautiful. We walked over a dizzying array of shapes and colors created by both pahoehoe and aa flows, some of which were younger than me. In general, the older flows, being more oxidized, took on a rustier-brown appearance.

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younger aa lava (left) and older pahoehoe (right)

Below is a view of the NE Rift of the volcano, the source of much of Mauna Loa’s recent lavas. The view’s from Red Hill, an 8600 year-old cinder cone. There’s a hut at Red Hill where we spent our first and third nights.

NE Rift, Mauna Loa Volcano

NE Rift, Mauna Loa Volcano. (geologypics: 170918s-149)

Our second day, we walked up the NE flank, across and along lava flows all erupted within the last 200 years. And cinder cones –and spatter cones–and, and, and!

Pahoehoe basalt and cinder cone, Mauna Loa

hiking on pahoehoe basalt flow; cinder cone in background. (geologypics: 170917s-14)

And here’s my favorite cinder cone, at an elevation of about 12,500. It’s called Pohaku ‘ohanalei –and you can see a pahoehoe flow coming right out of it! And it’s really glassy–look at how reflective it is. In fact, most of the flows were glassy.

Cinder cone and lava flows, Mauna Loa

Pohaku ‘ohanalei. Cinder cone and pahoehoe. (geologypics: 170917s-49)

Once you reach the elevation of 13,000′,  you cross a couple big cracks that are part of the rift zone and then you walk across a frozen lava lake. The lava lake fills the so-called “North pit” of the summit caldera and is partly filled with lava from 1984. 1984… I’m older than that.

Frozen lava lake, Mauna Loa

Frozen lava lake in north pit of caldera; summit of Mauna Loa shield volcano in background. Note the extrusions along fractures on either side of the surface in the foreground. (geologypics:170918s-55)

The Summit:

We spent our 2nd night in a hut on the southeastern rim of the caldera –directly across the caldera from the summit. Our plan was to get a good start in the morning and go back to the trail junction at about 13,000 feet where we’d drop our packs and hike the 5 mile trip to the summit and back, get our packs, and then hike down to Red Hill.

But first… the night sky from 13,250 in the middle of the Pacific, with the rounded summit of Mauna Loa in silhouette was something I’ll never forget. Cosmos and Cosmic–I fell in love. Here’s the sunrise view. The cracks form along the edge of the caldera–the floor of which is some 150-200′ straight down.

Summit caldera and fractures, Mauna Loa, Hawaii

Summit caldera and ring fractures, Mauna Loa at sunrise. (geologypics: 170918s-11f)

That morning, we hiked to the trail junction and dropped our packs and walked up to the summit. It was nice to not carry anything except a camera! Here’s a photo from near the top –it shows a pahoehoe flow coming from …space!

Edge of summit caldera, Mauna Loa

Western edge of summit caldera, Mauna Loa –showing pressure ridges in frozen lava lake and older basaltic lava flows. Pahoehoe flow in foreground is cut off by caldera ring fault. (geologypics: 170918s-68)

That’s because the lava predates caldera formation –the other side of that lava flow is buried under all the new lava that now fills the caldera.  And here we are! I forgot to brush my hair. By the time we got back, I had some nice dreads going.

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Summit selfie! Marli (left), Lindsay (center), Morgan (right).

We got back to the trail junction at about 12:30pm –where we saw the only other people of the whole trip –they were taking a day hike from the Mauna Loa Observatory, which you can reach by car from the Saddle Road.

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Orange peels are NOT biodegradable

That’s also where I noticed these orange peels. Orange peels! Really? Orange peels dry out and get hard and DO NOT BIODEGRADE –unless you give them something like 1000 years. There’s also a punch of toilet paper scattered about up there. Come on people! Pack out your crap!

 

The Descent:

Back at our packs, Lindsay pointed out (again) how little time we had to get back to the hut at Red Hill, 9 miles away–unless we wanted to get stuck on the lava flows when it was dark. So we bombed down the mountain at what felt like 90 mph (it was more like 2mph, actually) –and we reached Red Hill with an hour to spare. And the views? Awesome!

Pahoehoe and aa basalt, Mauna Loa

Pahoehoe (left) and aa basalt, Mauna Loa. Dewey Cinder Cone in background. (Geologypics: 170918s-103)

I especially loved seeing Mauna Kea, which we could see from Mauna Loa’s summit all the way down to Red Hill. Mauna Kea is the big shield volcano next to Mauna Loa, and actually a little higher. If you compare their overall sizes on the geologic map though, you’ll see that Mauna Loa is still a lot bigger.

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Mauna Loa Volcano from Red Hill

And here’s Morgan watching the sunset from Red Hill.170916s-45c

 

And finally…

…back to the immensity of this volcano. The day before we started our hike, we drove around to the other side of the island to the town of Captain Cook where we  snorkled at Kealakekua Bay. It turns out that the lava flows in the sea cliffs are also part of Mauna Loa –you can see that on the geologic map (Kealakekua Bay is marked). That’s actually the profile of the volcano in the background. And those sea cliffs are there because it’s the head scarp of a giant undersea landslide!

GeologyPics-170915s-10c

Sea cliffs at Kealakekua Bay, formed as the headscarp of an undersea landslide (Geologypics: 170915s-10c)

 


Most of these photos are freely downloadable at slightly higher resolutions from my website: Geologypics.com. You can type the id number (visible in the photo’s caption) into the keyword search –or you can just type “Mauna Loa” into the search to see these and a whole lot of other images!

Thanks for looking.

 

 

 

 

 

 

 

 

 

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…

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.

G.110805-122cs

 

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

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