Earth as Inspiration: Mt. Shasta for Earth Science Week, October 14-20

Mt. Shasta and Shastina from the north

I usually don't need an inspiration to write about Mt. Shasta, but I realized (two days in) that October 14-20 is national Earth Science week, and the theme of the celebration this year is "Earth as Inspiration". In case you have not yet realized this yet, but I am in fact inspired by the Earth. It started early on in my life with family vacations to some stunning places in California and the American Southwest, continued with scouting experiences nearly every weekend in my teens that included extensive work with topographic maps, and right into my college major and subsequent career as a geology professor. And then I found the form of story-telling called blogging in 2008.

Panther Meadows at the 8,000 foot level on Mt. Shasta

Mt. Shasta is an earthly inspiration. We visited two weeks ago as part of our field course on California's volcanoes. The stops included a drive to the end of the highway at Panther Meadows at 8,000 feet on the side of the 14,179 foot high volcano, and another stop on the north flank where we could see the glaciers and one other astounding feature of the volcano (mentioned below). Shasta is the second tallest volcano (behind Mt. Rainier) but is the most voluminous composite cone (stratovolcano) in the range (I'm parsing words here; there is a larger volcano, but it is of a different kind and will be discussed in a future blog). As a classic composite cone, it is composed of the remains of at least four previous incarnations, capped by the current active vent, Hotlum Cone. The oldest lava and ash dates back to around 600,000 years ago, but the youngest is a mere couple of hundred years. It likely erupted in 1786.

As the highest mountain in Northern California, it supports seven glaciers. Whitney Glacier, with a length of two miles, is the longest in the state (below). The glaciers are responsible for one of Shasta's unique hazards: jokulhlaups! These are floods caused when meltwater is sealed underneath the glacial ice which then breaks out in a catastrophic manner. Although caused by eruptions under the glacial ice in places like Iceland, those that occur on Shasta can happen almost any time. They are generally more of a nuisance, messing up roads and bridges, rather than a killer.

The biggest dangers of a volcano like Shasta are volcanic mudflows (lahars), and hot ash flow eruptions. Lava flows, unless they interact with the ice, are of a lesser concern. Andesite lava has a pasty consistency and is not likely to flow overly far from vents on the mountain. Lahars are of the greater concern, as they are capable of producing massive casualties and structural damage. The towns of Mt. Shasta, Weed, and McCloud are constructed on old lahar deposits. Major events could cause the closure of Interstate 5. Hot Pompeii-style ash eruptions are somewhat less likely, based on the previous history of the volcano.

Whitney Glacier, the largest in California

One of the most outrageous landscapes to be found anywhere on the planet lies to the north of Mt. Shasta. When compiling geologic maps of the region in the 1970s, geologists weren't sure how to interpret the vast region extending north from the mountain reaching 28 miles to the edge of the village of Yreka. It was a hummocky landscape, made of hundreds of small hills and cones of lava fragments with intervening hollows, some containing lakes and ponds. Was it some kind of odd field of cinder cones? It didn't make a lot of sense until the eruption of Mt. St. Helens in 1980.

The St. Helens eruption was initiated when an earthquake caused the entire north flank of the volcano to collapse in a gigantic debris avalanche that traveled for twelve miles down the Toutle River valley. Humans had never witnessed a landslide so large. It uncapped the volcano, leading to the very explosive ash eruption that followed.

To the geologists studying the region around Shasta, it was a revelation. The avalanche at St. Helens formed hundreds of hummocks similar to those found at Shasta. It quickly became clear that the deposit on the north flank of Shasta was the remains of a gigantic debris avalanche. The St. Helens avalanche involved less than a cubic mile of material (0.67 cubic miles), but the now-apparent debris avalanche at Shasta was ten times larger (about 6.5 cubic miles), and it traveled twice as far. It seems to have happened between 360,000 and 300,000 years ago. It's stunning just to image seeing something like this happen.

What aspects of the Earth do you find inspiring?

The Hawai'i That Was: What the Worst Disaster You Can Think of? The Terror of Na Pali...

Wait, what? Terror? Na Pali? That place isn't terrifying, unless you have a fear of heights. It's one of the most beautiful places on one of the most beautiful islands in the world. What could be scary about it?

Well...there's history, and geology. What's the worst disaster you can imagine happening in the place where you live? Are big earthquakes possible? Volcanic eruptions? What about hurricanes or tornadoes? On our adventure today, we visit the site of one of the greatest natural disasters possible.

Kaua'i is a modest island by Hawai'i standards, covering only 553 square miles, fourth in size after Oahu, Maui, and the Big Island. Unlike the other islands, it was principally a single basaltic shield instead of four or five like the Big Island and Maui (it's a little more complicated than that, but I will deal with that story later in another post). It's also the oldest of the major islands, at about 5-6 million years. The coastal areas of the island are of mostly gentle topography, but on the northwestern side of the island, that gentleness ends. Dramatic cliffs 3,000 feet high drop precipitously into the Pacific Ocean. Welcome to the Na Pali. Why are these incredible cliffs here? And what does that have to do with disaster?

Try to imagine a much younger Kaua'i maybe 4-5 million years ago. The shield volcano rises to an elevation of perhaps 8,000 feet above sea level, and the slopes of the mountain are covered with dense rainforest. Myriad species of birds fly among the trees, along with thousands of species of insects and gastropods. All of them are unknown to humankind, because the kind of humans that would pay attention to such things would not be present in the world for a long time. All that was here was about to be lost.

The islands may feel permanent and unchanging in some ways. The lava flows that emerged from the shield were solid and hard and one might feel that they would not be easily eroded or altered by time. That's a delusion, of course. The volcanic rocks were originally deposited on the sediments of the seafloor, and many of the original lava flows were composed of relatively unconsolidated rock, small cinders and ash layers that are not nearly so solid as the lava flows above. The sheer weight of the overlying lava flows exerted such tremendous stress on the unconsolidated rocks that they destabilized and commenced slowly giving way in a lateral sense. The flanks of the island were weakening.

It's not at all entirely clear how the end came about. There may have been earth movements for centuries, maybe even violent earthquakes that produced scarps high on the flanks of the volcano. Such cliffs can be seen today on the southeastern margin of the Big Island near the Kilauea caldera. The quakes may even have produced small tsunamis that swept across the lower shores of the island. But these events would not have affected the animal of the rainforest all that much.

Maybe there weren't any warning signs. I find that to be less convincing, but maybe the end came suddenly, with no precursors. It didn't matter then, but we'd sure like to know today what transpired, because it would be nice to have some warning when an unimaginable tragedy is about to strike.

In any case, the final stroke must have come quickly. Who knows what kinds of sounds were heard as a significant percentage (a fifth? a quarter?) of the entire island suddenly broke away and sank into the sea? The collapse was so rapid that the debris flowed for sixty miles (100 km) along the sea floor. The rapidly sinking land broke up into large chunks and disappeared beneath the turbulent waves. Some of the fragments were miles across. The homes and habitats for hundreds of species disappeared in an instant, never to be seen again.

The loss of a significant part of the island beneath the waves was only part of the story. Displacements of ocean water on this scale produce tsunamis of unimaginable size. We aren't talking about the 30'-40' high waves of events like the tragedies of Indonesia in 2004 or Japan in 2011. We are trying to imagine a wave that exceeds a height of 1,000 feet. Or considerably more. There are chunks of coral on the island of Lanai that presently sit 1,300 feet above sea level. And Lanai is and always has been slowly sinking. Those blocks of coral were tossed there by mega-tsunamis that were produced by similar catastrophes on other nearby islands.

So first, a huge portion of the island sinks into the ocean, and then the water rises in response and sweeps across vast swaths of Kaua'i and the other Hawaiian islands. The level of destruction is incomprehensible. How many species went extinct that day? No one can ever say. Where a coastal plain once existed, there were only cliffs. Immense cliffs. In time, vegetation returned, and erosional processes sculpted the escarpment into the beautiful fluted cliffs we see today along the Na Pali coastline.

One immediately has to wonder whether it could happen again. The answer is, of course, sure. But these events thankfully don't happen often, maybe once every 300,000-400,000 years. And for now, knowing they have happened in the past, we'll perhaps recognize some of the warning signs that such a slide is again imminent. For the time being, we can instead appreciate the beauty that emerges from catastrophe.

The cliffs of the Na Pali are a bit difficult to see. You can drive to Kalalau or Pu'u o Kila lookouts above Koke'e Park and look down from the cliff tops to the sea (see the top picture in this post). These are two of the most astounding views I've ever seen in my life. You can walk the 11-mile long Kalalau Trail that winds along the base of the cliffs (an adventure I've longed to try). Or you float in the sea offshore for an astounding view. Some people take kayaks (another dream), and others take cruises. I had that opportunity in 2006, and that's when I took most of these pictures.

This post is part of a long-running blog series on the geology and history of the Hawaiian Islands, based in part on our summer field studies journey of last June.

What's Burning Up Tonight: The Blue Cut Fire in Southern California

Source: http://www.fire.ca.gov/general/firemaps

California is burning. Sometimes, the fires are burning in unfamiliar places, places we've never visited. Logically, we know they are tragedies, that people are losing their homes, that beautiful forests are disappearing, but there's nothing quite like having a familiar place go up in flames.

Fires are part of the natural landscape, an outgrowth of a Mediterranean climate where no rain falls for six months out of the year. Plants and animals are adapted to fires. But things have changed, and some of the fires have become terrifying disasters. First of all, the growing population is expanding into ever more dangerous terrain, places that burn regularly, whether developed or not. But second, the effects of global warming are intensifying droughts that have left most of California dry and vulnerable.

The Blue Cut Fire is burning in an area I know well. I grew up at the foot of Lytle Creek and Cajon Pass, and have traveled over the pass perhaps hundreds of times over the years. The fire exploded in one day to more than 25,000 acres, and conditions offer little hope of any type of containment very soon. An unknown number of structures have already been destroyed, and an unprecedented 35,000 houses are threatened in places like Wrightwood, Phelan, and Lytle Creek. Something like 80,000 people have been evacuated. I hope and pray that it will be contained and controlled soon with a minimum of damage.

I wrote about the region a couple of years ago. Lone Pine Canyon is in the middle of the area that is burning, so the places seen in these pictures will be looking very different now. What follows is my post of March 31, 2013:

The Other California: Getting a Good Look at California's Faults

The San Andreas fault in Lone Pine Canyon near Cajon Pass in Southern California. Photo by Mrs. Geotripper

If there is anything that people know about California, it's the San Andreas fault. In a vague sense anyway...California has a lot of earthquakes that many people assume happen along the San Andreas (most don't), that there are occasional BIG ONES that happen on the fault (some of them, but not all), and if popular culture as expressed in movies like the original 1978 version of Superman reflects common knowledge, no one knows where it is or what it looks like (oh, and California is going to fall into the sea).

Still, the San Andreas is a fundamental part of the structure of California, and it is indeed capable of causing a great deal of seismic havoc, with some parts of the state considered at a high risk of moderate to large earthquakes. If one is curious about seeing the state's most famous fault line, there are a great many places to explore it, some in surprisingly visible locations. We are exploring one of them today in a segment of my "Other California" blog series.

Thousands upon thousands of cars follow Interstate 15 daily across Cajon Pass on their way to Las Vegas or their jobs in the L.A. Basin. I imagine few of the drivers know they are crossing California's most famous fault just a few miles north of the Interstate 15/Interstate 215 above San Bernardino. For a few moments, travelers are treated with a spectacular view up the linear track of Lone Pine Valley (the picture at the top of today's post shows the view, taken at 65 mph). I explored the lower end of Lone Pine Canyon and the "mysterious" Lost Lake (really not mysterious) in a post several years ago (click here to see it), but a weekend or two ago I had a chance to explore the upper end for the first time in a few decades.

The Mormon Rocks (or Rock Candy Mountains) expose the 18-20 million year old Cajon Formation. Interstate 15 climbs towards Cajon Pass on the skyline.

The road through Lone Pine Canyon takes off from Highway 138 about a mile west of the junction of 138 and Interstate 15. The road climbs through some beautiful exposures of the Cajon Formation  (the tilted exposures of the arkosic sandstones and conglomerates are called the Mormon Rocks or the Rock Candy Mountains; I've written about them before). The rocks have been tilted and folded due to their proximity to the San Andreas fault. The road surmounts a low pass and drops into Lone Pine Canyon.

The San Andreas fault is not a single break, but is instead a half-mile wide system of different slices of crust. Constant shearing over the last few million years by fault motions has left the rock fractured and easily eroded, forming the distinct linear valley of Lone Pine Canyon.

The series of fault blocks have formed a series of benches and scarps on the southwest side of the canyon, and a few offset channels are easily seen in the chaparral-covered hillsides (above).

Approaching the upper end of Lone Pine Canyon, we can see an odd hill in the middle of the valley. Looking at the steep slope to the right, it is apparent that we are looking at a rather large debris avalanche, caused no doubt by an earthquake along this stretch of the fault (above). The road skirts the lower end of the slide, confirming the nature of the hill with the broken and brecciated rock (below). There are plenty of candidates for the causative event; major earthquakes happened along this stretch of the fault in 1857(info here), 1812 (info here), and as many as a dozen other times in the last 1,500 years. There is a distinct warning in the earthquake history for this stretch of the San Andreas: the recurrence interval of large quakes is just over a century but it has been more than 150 years since the last major event.

The road reaches the top of the canyon, and a short walk along the ridge at the summit provides a spectacular view back down Lone Pine Canyon towards Interstate 15, and the two largest mountains in Southern California, San Gorgonio Peak and San Jacinto Peak. The fault passes between them on the way to Palm Springs and the Salton Sea.

 There is a large outcrop at the head of the canyon that exposes highly sheared rocks from the fault zone. The original rocks may have included the Pelona schist and granitic rocks but they are almost unrecognizable in hand samples.

But one thing is kind of cool: how often can you hold a major fault zone in your hand?

The road through Lone Pine Canyon ends in the village of Wrightwood, the subject of our previous post about a recurring mudflow originating in the Pelona Schist on the high ridges above. As if they didn't have enough to worry about...

The Other California is my continuing blog series on the geologically fascinating places in our fair state that don't always make it onto the tourist postcards.

The Hawai'i That Was: Exploring Pololu Valley on an Unstable "Dead" Volcano

Do the signs add a hint of an element of danger to this hike?

The stereotypical image of Hawai'i includes many things (most of which are seen in the opening credits of Hawaii Five-O), but one of them is surely the dramatic fluted cliffs clothed in tropical vegetation. It's not hard to understand why, since most tourists visit Oahu, and most of the mountains there are quite steep. The Big Island of Hawai'i is often a surprise, then, because there just aren't that many dramatic sheer cliffs. The island is composed of young shield volcanoes like Mauna Loa, Mauna Kea, or Kilauea, and shields have gentle slopes.

This is most surely not a "gentle" slope.

There is one major exception. The older shield of Kohala on the northernmost tip of the island has a twelve mile long stretch of coastline that is composed of dramatic cliffs and deep valleys. The Pololu Valley is found at the north end, while Waipi'o Valley forms the southern end.The cliffs are rugged enough that no roads penetrate the coastal wilderness. Kohala began erupting around a million years ago, with the latest flows occurring around 120,000 years ago.

Source: U.S. Geological Survey

We would expect older volcanoes to display a great deal more erosion, but that's only part of the story at Kohala. The rest of the volcano has no similar sea cliffs. Something else happened here. New technology for accurate mapping of the sea floor offshore of the Hawaiian Islands has provided a useful clue. There is chaotic debris on the ocean floor at distances reaching as much as a hundred miles. The islands have been falling apart!

It is difficult to imagine the scale of these events. The largest debris avalanche ever witnessed by humans was the one that came off the flank of Mt. St. Helens during the eruption of May 18,1980. It traveled about 12 miles. An avalanche off the side of Mt. Shasta in California traveled about 28 miles, but no one was about to see it happen, seeing as how it is more than 300,000 years old.

When the flanks of the Hawaiian Islands collapsed, the runout was more than 120 miles at Molokai, and 80 miles below the cliffs of the Pololu Coast. The sudden displacement of sea water by the rock generated devastating mega-tsunamis. One such event left chunks of coral reef 1,300 feet above sea level on the island of Lanai.

Don't worry too much about killer tsunamis on your vacation journey. As horrific as they are, they take place at intervals measured in the tens or hundreds of thousands of years, and there are no signs that any are imminent. The Pololu avalanche took place about 120,000 years ago.

A short but steep trail leads from the end of the road to the valley floor several hundred feet below. It travels farther out across the coastal cliffs providing a better view of the beach cliffs along the coast south of Pololu.

The floor of the Pololu Valley is surprisingly flat, and one might wonder that people aren't living and farming here. They once did in large numbers, but the taro fields were destroyed by a series of more "normal" tsunamis in the twentieth century, and the fields have been abandoned. There is a rich archaeological record of farming and housing sites all along the valley.

They collected rocks too. Not for their intrinsic beauty, mind you, but to construct an impressive heiau at Pu'ukoholā on the other side of the volcano, more than twenty miles away. Heiaus are large temple sites composed of hundreds of thousands of boulders that were passed hand-to-hand between thousands of "volunteers" working for King Kamehameha in the late 1700s. The workers could face punishment for dropping a stone and breaking up the rhythm of the line.

The beach is composed of black and gray sand. There is also a system of sand dunes higher up the beach. Dunes are relatively rare on the islands, but wind blew coastal sands into a series of dunes reaching an elevation of 100 feet. Enjoy the pools, beach and dunes, because the hike up is quite steep.

Waipi'o Valley along the Kohala Coast

We weren't able to stop at the valley on the other end of the Kohala Coast, but Waipi'o Valley is very much worth a visit if you are on the Big Island. There are some stunningly high water falls in the upper valley.

Running Circles Around California's Greatest Volcano

From the northwest, Shasta and Shastina are two prominent peaks.

I'm going to get into rhetorical trouble for this. "Greatest" is a hugely subjective term, and there are going to be some disagreements. But Mt. Shasta is California's greatest volcano. Not necessarily my favorite (though it might be), but the greatest. How does one judge such thing? My standard of the day is topographic prominence and topographic isolation.

A gigantic debris avalanche covers the countryside for 28 miles north of Shasta.

Topographic prominence is the elevation difference between the summit and the highest or key col to a higher summit. Topographic isolation is the minimum great circle distance to a point of higher elevation. By those metrics, Mt. Whitney, the highest point in the state has the greatest prominence and isolation. It's 1,646 mi (2,649 km) to another mountain that is higher than Whitney, and it has a prominence of 10,080 ft (3072 m). But Whitney is surrounded by dozens of mountain peaks that are nearly as tall. It doesn't exactly stand out. But Mt. Shasta stands alone, with a prominence of 9,832 ft (2997 m), and it is 335 mi (539 km) to another peak that is higher (in the Sierra Nevada). In short, Shasta is a huge mountain that provides an awesome sight from all compass directions. And that's what today's pictures are about.

Last week we took four days to completely circle Shasta, first traveling north on Interstate 5 to pass by the western flank of the mountain, then following Route 97 to swing around the north side. We took Route 161 along the Oregon border to get to Tulelake and Lava Beds National Monument for a view form the northeast. We then drove over Medicine Lake Highland for a look at the south flank.

Whitney Glacier is the longest glacier in California, and the only valley glacier.

Shasta has a few other distinctions. It has the largest and longest glaciers in California (above). Whitney glacier is 2 miles (3.2 km) long, while adjacent Hotlum glacier covers 0.7 square miles (1.8 km²). Both glaciers have grown in size over the last fifty years, seemingly at odds with global warming. The growth is explained by increased precipitation over the years (from higher evaporation rates over the warmer oceans), even though temperatures in the region have increased 2-3 degrees. As warming continues, the growth spurt will end, and so probably will the glaciers themselves.

Sandhill Cranes pause in their migration at the Tulelake National Wildlife Refuge on the northeast side of Shasta

Another strange aspect of Shasta is the unusual hummocky surface that extends north from the mountain for 28 miles (43 kms), almost to the town of Yreka. The lumpy surface is the remains of a gigantic debris avalanche that destroyed a previous incarnation of Mt. Shasta around 300,000 years ago. The avalanche was not recognized for what it was until a similar event traveled 12 miles from Mt. St. Helens in the eruption of 1980. The landslide is one of the largest ever documented in the world.

Shasta from the Tulelake National Wildlife Refuge

Volcanism has been taking place at Mt. Shasta for around 600,000 years, but most of the cone-building has happened within the last 200,000 years. Shasta is actually an edifice of four different cones that formed at different times. The Sargents Ridge and Misery Hill cones are the oldest, and the least obvious. Whitney Glacier follows the edge of the Misery Hill crater.

The southeast flank of Shasta from near Bartle.

Shastina erupted around 9,700-9,500 years ago, and the main peak, Hotlum Cone, has been erupting during the last 9,000 years. The most recent volcanic episode may have been only 200 years ago. Several villages have been constructed on the flanks of the volcano, including McCloud, Weed, and Mt. Shasta City. Around 20,000 people call the volcano home.

Unless you count the Lemurians. And the Atlanteans. Such a prominent mountain could not be without legends and myths, and Shasta has plenty. Tired half-conscious climbers have reported seeing survivors of the Atlantic disaster wandering the upper slopes, and an entire cottage industry swirls around the mysticism of the mountain, and all the beings who live in gigantic underground cities within the volcano. I suppose it all makes sense...

The biggest volcano in the Cascades, the biggest volcano in California, visible for a hundred miles or more in many directions, it's a great volcano. Maybe the greatest.

Northern Convergence: Tragedy at Crowsnest Pass

Frank was a coal mining town of around 600 people in 1903. The coal seam ran along the base of Turtle Mountain, so the town was established there as well. The Canadian Pacific Railway also crossed the area on its way to Crowsnest Pass.

The local First Nation people did not like Turtle Mountain. They called it the "Mountain that Moves", and refused to camp in the area. The Europeans had no such worries, and mining of the coal was well underway. In the early morning of April 29, 1903, a shift of 17 miners was working deep underground. For weeks there had been strange things happening in the mine. Timbers holding up the tunnel walls would splinter and break for no apparent reason. Coal would occasional "mine itself", crumbling out of the seams overnight when no one was around. Small earthquakes were occasionally felt underground. The miners knew that the collapse of mine tunnels was an ever-present danger, so they may not have been overly surprised to hear the explosive concussion followed by an ominous silence. They were trapped, no doubt by a cave-in. They began to assess their situation. Soon, water was pouring into the tunnels, making a bad situation even worse.

The normal passage to the surface was blocked, but one of the miners knew that a second coal seam might be close enough to the surface that they could hack their way out. They started digging for all they were worth, gasping in the increasingly toxic air. One by one, the miners gave out. They weren't dead, but they just did not have the energy to pick up their tools. Only three of them were still working when they broke through to the surface. Rocks were still falling from above, so they couldn't yet escape, but they had fresh air, and they quickly cut another opening beneath a protective overhang. After thirteen horrible hours they emerged at the surface to find their experience was only a part of an even larger tragedy. A gigantic avalanche had buried part of their town, killing between 70 and 90 people. The miners had been given up for dead, so their appearance was some small bit of good news in the midst of the horrific event.

It gets to a certain point when driving through the mountain wilds of British Columbia and Alberta that one expects that trees will be growing just about everywhere. The region has plenty of precipitation through the year so things will be green. Approaching Crowsnest Pass during our recent Northern Convergence tour, we were struck by the sudden appearance of an absolutely barren slope. It doesn't take long to realize why, as the highway crossed a huge debris field covered with gigantic boulders. It was the debris avalanche that destroyed so much of Frank back in 1903.

http://en.wikipedia.org/wiki/Frank_Slide

The slide was truly epic in scale. Totaling 30 million cubic meters (82 million tons), the avalanche was 1,000 meters (3,300 ft) wide, 425 meters (1,394 ft) high and 150 meters (490 ft) deep. It spread laterally over level ground, covering three square kilometers. The rocks had flowed over the surface like a thick liquid at speeds of up to 70 mph (112 km/hr). The entire event was over in less than 2 minutes.

 The slide was probably inevitable. The limestone layers had been folded into a huge anticline (upward pointing fold) with thrust faults at the base, on top of weak Cretaceous sediments. Glaciation had oversteepened the flanks of the mountain. Fissures sliced deep into the rocks allowing water and ice to accumulate, weakening and wedging the rocks apart. The mining at the base of the slope was quite possibly a contributing factor.

Source http://www.uleth.ca/vft/crowsnest/slidedebate.html

The Frank Slide was the worst mass-wasting disaster in Canadian history. But life went on. The mines were reopened (a horse who worked in the mine was actually found alive after a month underground). The town grew even larger for a few years, but by 1917 the coal mines closed down. Today about 200 people live in the village nearby, and an interpretive center has been constructed that provides information on the extraordinary event.

We headed into nearby Pincher Creek for the night. It was our last night in Canada, but we still had plenty yet to see, on both sides of the border..

Source: http://occ.crescentschool.org/geography/physical/folding/frankslide.html

A Moment of Volcanic Clarity: Rainier and St. Helens Show Themselves

I'm up in the Pacific Northwest for family things (it's the holidays after all), but I've been on the hunt for Cascades volcanoes during our journeys from one place to another. True to Pacific Northwest form, the weather hasn't cooperated. We drove north through Portland and Seattle a few days ago through scattered rainstorms, and when the time came to drive south again, an inversion layer set in and fog was everywhere. But we had one moment of clarity. As we came over a rise near Napavine, we broke out over the inversion layer, and had a moment to see Mt. Rainier.

Rainier is a huge mountain. It is 14,410 feet tall (4,392m), and is covered by 156 billion cubic feet of glacial ice. With its location so close to large population centers, it is one of the more dangerous of the Cascades volcanoes, although it hasn't been active in historical time. The last eruption was around 1,000 years ago. But a number of towns are built on mudflow deposits (lahars) from Rainier, highlighting the hazardous nature of the volcano.

We drove back into the fog for a few more miles, and took a chance and headed east from Castle Rock to see if anymore volcanoes would be visible. At Silver Lake about 5 miles in, the clouds cleared and we were blessed with a stunning view of Mt. St. Helens. There is a multi-agency visitor center at the lake, and a nice nature walk that extends out into the lake on a small levee and boardwalk.

Silver Lake is an interesting volcanic feature itself. The 1980 debris avalanche that precipitated the eruption of Mt. St. Helens was not the only mass wasting event that has happened in this area. The landslide in 1980 dammed several side canyons, creating several lakes, most notably Coldwater Lake.

2,500 years ago, a similar event took place, and several lakes were formed near the volcano. When one of the lakes overflowed and failed catastrophically, the ensuing flood carried debris downstream, blocking the drainage now covered by Silver Lake.

The lake must be a sea of green in spring and summer, but here in winter, the plants were frozen and wilted away. There wasn't much in the way of animal life present, but a blue heron was perched in a tree where it could be framed by the peak of Mt. St. Helens.

St. Helens is deceptively serene today. The debris avalanche and violent eruption of 1980 are justly famous, and explosions continued through 1986. The mountain reawakened in 2004, and erupted quietly for four years, building a second volcanic dome in the crater of the mountain. The second eruption was nowhere near as famous as the first for the obvious reason: no one died.

Several good paved highways approach the mountain, and several visitor centers can be found along Highway 504 above Interstate 5 on the west side of the volcano. We had little time for exploration, but we enjoyed the walk along Silver Lake, which is only five miles east of the Interstate.