Airliner Chronicles: Do You Know California's Biggest Volcano? You May Be Surprised at the Answer

The summit complex of Medicine Lake Highland, with Glass Mountain at the top, the Medicine flow center-left, and Medicine Lake at center-right.

It's a real problem for a geologist to be flying through cloud cover. One loses track of time and location so when an opening in the clouds occurs, one cannot know for sure where one is. I can pick out the essential geologic details a lot of the time, but without temporal or spatial context, I can't recognize even some of the most familiar places that I've visited many times. That's what happened last Thursday when I was flying to SeaTac. I lost sight of the ground only a few minutes out of Sacramento, and when the ground reappeared again, I was totally fooled by the scenes in these pictures. I thought I might be over Newberry Crater in Oregon, but I couldn't place Paulina Lake with the steep ridge that should have been to the right in the picture above. So I figured it must be some place in the Three Sisters area that I wasn't familiar with. But then I got home and looked at the pictures on the computer instead of the camera. I was wrong.

The Medicine Flow dates to about 2,000 years ago. It is composed of thick dacite lava flows. Frozen Medicine Lake is to the right.

It turns out I was flying right over the top of California's biggest volcano. Mt. Shasta is California's most prominent volcano, rising to 14,162 feet above sea level. It's the largest stratovolcano in the entire Cascades chain, with more bulk than even Mt. Rainier, which we looked at in our previous post.

[At this point there is a bit of uncomfortable shuffling in the back of the room as a few of the geologists look at each other and start mumbling something unintelligible.

"Ahem, is there something you would like to add to the discussion?" I say.

"But we've seen Mt. Shasta, and it looks nothing like that".

"And you would be right" I say, "but give me a chance to finish". They relent.]

But this isn't Mt. Shasta. It may be the tallest volcano in California, and it may be the biggest stratovolcano in the Cascades, but we are forty miles northeast of Shasta, looking at an entirely different kind of volcano. It's a shield volcano called Medicine Lake Highland. Although it is not even 8,000 feet high, it is much wider, with a total volume of around 130 cubic miles, compared to about 108 cubic miles for Mt. Shasta.

The view from the ground shows a gently sloping edifice covered by a variety of cinder cones and plug domes. Medicine Lake Highland (MLH)is shield-shaped like the giant volcanoes that make up the Hawaiian Islands, and is composed in large part of basalt, the fairly non-viscous lava that can flow for long distances before congealing. But MLH is different in some important ways. Some of the magma chambers beneath the volcano originate in the crust rather than the mantle (dacite or rhyolite), and the silica-rich lavas that erupt at the surface are sticky and barely flow at all.

MLH is an active volcano. There have been at least 17 eruptions in the last 11,000 years, and the Glass Mountain flow (below) erupted only about 850 years ago. There are areas of geothermal activity that have been proposed for energy development, but these have been rebuffed so far (thank goodness).

Glass Mountain at the top of Medicine Lake Highland. The flow dates to 850-900 years before present.

The top of the shield complex is a caldera (a sunken crater-like depression caused by the inward collapse of the top of the volcano). It is about the size of the Crater Lake Caldera, but is not nearly as rugged, as it is many thousands of years older and has been partially filled with subsequent lava flows. Medicine Lake sits within the caldera, but is not volcanic in origin. During the ice ages, glaciers scoured the summit area of MLH and left behind some impermeable clay deposits that prevent water from sinking into the ground (there are very few streams or rivers on the volcano, as it is highly porous; massive springs are found around the base of the volcano.).

One of America's most interesting national monuments is found on the north flank of MLH. Lava Beds National Monument preserves more than 75 miles of underground lava tubes, one of the highest concentrations of such caves in North America (and maybe in the world). The park also preserves the memory of the last stand of the Modoc people in their struggle against the U.S. military in the 1870s. They held out for months in the barren lava flows but were finally betrayed and captured. The Modoc people survive, but much of their cultural history was lost when they were banished to Oklahoma.

The clouds soon closed in again and I saw nothing more until we were over Washington.

The Hawai'i That Was: How Can the Biggest Mountain in the World Stay So Hidden?

Mauna Loa from the Mauna Kea Road near the Onizuka Center

The answer is easy: clouds. This whole post is a temper tantrum, a tantrum that resulted from the fact that we were on the Big Island of Hawai'i, the site of the biggest mountain on planet Earth, for nine days a few weeks ago. Despite repeated opportunities, my students never had a clear view of Mauna Loa, the volcano that covers more than half of the island. It was a rainy stretch of weather, so the best we ever got were brief peeks, kind of like watching an old-fashioned feather boa dance. So in response, I've drawn from the Geotripper archives to find pictures of Mauna Loa from earlier trips. Very sunny trips.

Mauna Loa from the Mauna Kea Road near the Onizuka Center

Clouds are not the least bit unusual on the slopes of Mauna Loa and Mauna Kea, the two highest peaks on the planet (as measured from the sea floor; of the two, Mauna Kea is slightly higher). The Hawaiian Islands lie in the path of the trade winds most of the year, and as the moist air masses rise against the gentle slopes of the massive shields, they cool and condense into clouds. Hilo is pretty much the wettest city in the United States, with more than 100 inches of rain each year. Oddly enough, an atmospheric inversion layer limits cloud formation to the lower slopes of the volcanoes. It's been more than once that I've left Hilo in a rainstorm only to find crystal clear skies up on the mountain (but not so much last week!). Exceptions, like earlier this month, happen when storm fronts come through. In winter, snow is not a rare occurrence on the high peaks.

Mauna Loa from the Mauna Kea Road above the Onizuka Center

Oceans have a lot to do with the fact that no one gets to see the entirety of Mauna Loa. It is the biggest mountain on the planet, as well as the biggest volcano (although the Tamu Massif may be more voluminous), but it rises of the floor of the Pacific Ocean, with around 17,000 feet hidden beneath sea level.  A bit less than 14,000 feet rises above the waves. It depresses the sea floor another five miles, so the mountain could actually be said to be 56,000 feet high. It has a volume of 15,000-19,000 cubic miles.

Sunset on Mauna Loa from Mauna Kea. The brown air is vog from the eruptions at Kilauea on the other side of the mountain.

The volcano began erupting perhaps 700,000 years ago, and became an island around 400,000 years ago. It's hard to confirm since the older lava flows are hidden deep beneath the younger ones. The oldest exposed lavas (at the Ninole Hills) are about 200,000 years old. The giant shield continues to be very active, with 33 eruptions since 1843. The last eruption was in 1984, making this quiescent period the longest in recorded history (contrast that with the continuous eruptions at nearby Kilauea that started in 1983). The lava from the 1984 eruption came uncomfortably close to Hilo.

Mauna Loa from South Point, the imaginatively named southernmost point in the United States.

The gentle slopes of the volcano belie the true immensity of the mountain. To hike from the shoreline to summit is to simulate a trip from the tropics to the Arctic Circle. The slopes above 4,000 feet are among the most important bird habitat in the nation. Hawai'i is a gigantic open laboratory of evolution and the many native species have been decimated by environmental disruptions caused by the arrival of humans and their pigs, goats, rats, and mongooses. Even worse was the arrival of mosquitoes in the 1870s, as they are a vector for transmitting avian malaria. The native birds had no immunity. The mosquitoes can't thrive in the cooler conditions above 4,000 feet, so the mountains are an island within an island, providing sanctuary for the remaining survivors.

Mauna Loa looks almost insignificant in the morning light from Hilo Bay (below), but the summit is around forty miles away. The mountain is gigantic, and dangerous. And we barely got to see it earlier this month. But we knew it was there. We were surrounded by its flows in Hilo, at Hawai'i Volcanoes National Park, at South Point, and at Kona, a drive that took us 120 miles!

Mauna Loa from Hilo Bay