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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.

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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!

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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…

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!

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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