Monday, August 14, 2017
Friday, August 11, 2017
After the Disasters that Formed the Crater Lake and Crooked River Calderas, St. Helens was Hardly a Blip...Right? Uh, Right?
Which brings us to the next destination from our field studies journey through the Pacific Northwest last June: Mt. St. Helens in southern Washington. Every school child for the last 37 years knows the familiar profile of the mountain as it exists today, and vaguely knows that it looked much different prior to 1980. It appears in pretty much every science textbook in the United States, being the last volcano to erupt in the lower forty-eight states.
Mt. St. Helens prior to the May 18, 1980 eruption. Source: U.S. Geological Survey
The problem these days is that for many people, St. Helens is ancient history. It is a geological event that took place years before they were born, and as such there is a disconnect regarding the reality and intensity of the events that took place in 1980 and the years following. I'm even guilty of belittling the event by comparing it to the prehistoric eruptions that happened in the region thousands and millions of years ago
|Mt. St. Helens in 2002. Note the lava dome in the crater interior|
The eruption began in March of 1980 when a moderate 4.1 magnitude earthquake shook the mountain, the largest ever recorded. Geologists were concerned and wired the mountain with whatever sensors they could think of. The rising mass of magma began to interact with groundwater and ice within the mountain, and a series of ash eruptions tore away at the summit of the volcano. The magma began to push outwards on the north flank of the mountain producing a 600 foot high bulge. Geologists were concerned about slope stability, but what happened was far beyond what they expected, or could even imagine. On May 18, 1980 at 8:32 in the morning, a magnitude 5.1 earthquake shook the bulge loose in a titanic debris avalanched that dwarfed any ever seen by humans. It thundered down the north flank, partly into Spirit Lake, with the remainder shooting down the Toutle River valley for 12 miles. Twelve miles.
The loss of the bulge meant that there was no longer any pressure holding back the gas-rich magma chamber, and it exploded with the power of hundreds of atomic bombs. The main blast was directed north and west, again towards Spirit Lake, and down the Toutle River valley. The ash was moving so fast (around 300 mph) it actually passed the fast-moving debris avalanche, so that in places the ash layer is actually covered by the avalanche deposits.
|Mt. St. Helens in 2006, during the eruption that began in 2004. Note the second dome in the crater, behind the first.|
USGS geologist David Johnston, monitoring the volcano from an observation station on the ridge that now bears his name was one of the first people killed by the blast. Despite the evacuation orders (which were not far enough away from the volcano anyway), 57 people died.
These are just numbers, and numbers can't always describe the totality of the destruction of this volcanic eruption. You pretty much have to stand in the middle of it, and walk it. My first exposure to the devastation came about dozen years after the main blast (smaller-scale eruptions continued through 1986). I drove to the Windy Ridge Observation Point on the east side, which at the time was the only real viewpoint. The mountain was socked in by clouds (I had one brief glimpse of the outline of the volcano), but mile after mile of downed forest drove home the magnitude of the devastation.
We headed down the hill to our camp at Seaquest State Park at Silver Lake. We had been privileged to see most of the volcano, and gained a perspective of the devastation from the ground. I wished I could have shown my students even more, and was reminded of a flight I took to Seattle a number of years ago. It happened to be one of those rare perfectly clear days, and the flight was only half full. The stewards gave me some dirty looks as I gleefully jumped from one side of the plane to the other snapping pictures of Cascades volcanoes (I got great shots of every volcano north of Crater Lake to Mt. Rainier). And I got pictures of Mt. St. Helens from the air for the first time.
In the big picture of Earth history, the eruption of Mt. St. Helens will barely register as a blip. Unless future researchers find the debris avalanche deposits, the record of the eruption in most places will be a thin layer of ash, at most a few inches thick. It would be an unremarkable eruption. But the eruption happened in modern times. We had accurate records of the volcano as it existed before, and excellent documentation of the events of May 18, 1980 (had the day been cloudy, we would be confused by some of the deposits). And we know what the volcano looks like today. The changes by any human standard were huge, and the effects on society very large. There was nothing small about the eruption of Mt. St. Helens.
If you are interested in the St. Helens story, may I recommend an excellent series on the eruptions by fellow geoblogger Dana Hunter at Rosetta Stones (click here for the index). She did a stellar job of bringing the volcano to life, along with the stories of those who were affected by the disaster.
Thursday, August 10, 2017
It is the tan cliffs that really tell the story of catastrophe. It was a disaster so huge that its dimensions were not recognized until fairly recent times. The cliffs of Smith Rock are part of the northwest corner of the Crooked River caldera, a sunken crater that is 25 miles long and 15 miles wide. Crater Lake's eruption produced around 15 cubic miles of ash. The Crooked River eruption produced around 200 cubic miles. Imagine a dozen Crater Lake eruptions happening at once and you start to get an idea. The eruption rivals some of the worst of the disasters at Yellowstone or Long Valley in eastern California. The only saving grace here is that the eruption took place around 29.5 million years ago. The magma chambers that fed the event have long since cooled.
Modern human beings have never experienced an eruption of this magnitude. The last one of this size worldwide, at Toba in Indonesia about 75,000 years ago, may have almost done in the human race (a controversial idea, but plausible). It involved around 470 cubic miles of ash.
I notice that Smith Rock sits at the south edge of totality during the coming Solar eclipse. If you are lucky enough to get to the park as a setting for this once in a lifetime event, I hope you'll spend a bit of time pondering the incredible history of these rocks as well.
For some detailed information about the history of the Crooked River Caldera, check this link.
Saturday, August 5, 2017
The "crater" of Crater Lake is not a crater in the usual sense. It is a world-class example of a caldera, a volcanic feature that develops when a huge volume of ash explodes out of volcano, and the summit sinks into the void left behind. It was an unimaginable catastrophe. In the space of a few hours or days around 15 cubic miles of ash and debris were blasted into the atmosphere from the summit area of Mt. Mazama, the name given to the former volcano that became Crater Lake. What had once been a volcano as tall as 12,000 feet was now a smoking ruin with a rim barely exceeding 8,000 feet. The bottom of the caldera was another 4,000 feet lower. The ash was spread across the western United States and Canada, providing a crucial dating horizon for archaeologists (the ash has a unique chemical composition that can be identified in dig sites).
The Crater Lake caldera is young in the geologic sense, having erupted 7,700 years ago (+/- 150 years). Think about that: the ancestors of the indigenous people of the region saw and experienced this event. Their oral histories of the Klamath people recall the event. How many cultures in in today's world have collective memories that date back that far?
Tens of thousands of people on the island died from the eruption itself or starvation later (all vegetation on the island was destroyed). So much ash was blown into the atmosphere that the climate cooled to the extent that snow fell during the summer months over much of the northern hemisphere. Famine contributed to hundreds of thousands of deaths around the world.
Thursday, August 3, 2017
Some advice: DON'T LOOK AT THE SUN! You can destroy your eyes!
Good, now that we have that out of the way, what is this post all about? The sun has been on my mind the last few days. I'm preparing for the final adventure of the summer, and it has a lot to do with the sun, most specifically, the only eclipse to cross the lower 48 states since 1979, the first to cross the country in 99 years, and the last to cross the American West until 2045. I got to thinking about the singular events that I've seen over the years that involve the sun in some way or another.
The sun. A diameter of about 860,000 miles, more than 100 times the diameter of the Earth. About 93,000,000 miles away from Earth. Big enough to hold 330,000 Earths. Containing 99.86% of the mass of the Solar System. The source of energy that makes life possible on Earth.
The most obvious moments that we might pay attention to the sun are during sunrise and sunset. Every one is different and unique. At those times, the sun is at eye level, and the thickness (and dirtiness) of the atmosphere provide a bit of protection for viewing with the unprotected eye. As the sun passes across the horizon, light is split into bright colors of the spectrum, providing a beautiful spectacle. I've probably taken thousands of sunset and sunrise pictures over the years, but here are two of my favorites, a sunset in Newport California a few years ago (above), and sunrise over Lake Rotorua in New Zealand in 2004 (below). To this day I cannot keep straight my internal compass; I couldn't help but think the sun was rising in the west (it wasn't). Lake Rotorua is one of the world's rare geothermal regions with geysers. Hot springs in the lake account for the steam rising off the water.
A difficult phenomena to see related to sunsets is the green flash. It is a sudden flash of greenish light above the sun at the moment of sunset, and it is said to last only a second or so. As the sun dips into the horizon, the layers of the atmosphere will cause some of the sunlight to be refracted, with red and orange on the lower parts of the disk along with green (and rarely blue) across the top.
Rainbows involve the splitting of white light from the sun into its component colors of the spectrum. Caves and deep slot canyons provide another sort of splitting, that of the sun's energy into a more or less pinhole of light. I was exploring a lava tube in the Mojave National Preserve a few years back. It was dark inside, but there were a few small skylights, and the early afternoon sun came bursting through like a blast from alien phaser.
Another fascinating phenomena occurs when the Moon passes into the Earth's shadow, a lunar eclipse. They are not rare, happening around two times a year, and they can be seen simultaneously across the globe (as long as the moon is visible in the sky).
The picture above is one of my favorites because of the huge sunspots that were present during the Moon's transit across the disc of the Sun. If the eclipse occurs when the Moon is farther from the Earth (it has an elliptical orbit), an annular eclipse can occur, in which the Moon doesn't cover the entire disc of the sun. I caught the picture below in 2012.
And then there are the transits of the planets. These happen when a planet crosses the disk of the Sun. Only two planets can do this, Mercury and Venus, because they are the only planets with orbits that are closer to the Sun than Earth. I've witnessed two of them.
The rarest Sun-related event I've ever seen is a transit of the planet Venus. The one I witnessed happened in 2012 (below). Previous transits had been in 1874, 1882, and 2004. The next will not happen until 2117 (in December, if you are planning on watching).
The big event of all things Solar is of course a total Solar eclipse. As noted above, it's been decades since one took place in the lower 48 states, and next won't cross my neck of the woods until 2045. I'll be almost 90 years old if I make it that far. I've had the privilege of witnessing one, though, in 1991. It crossed the south end of Baja California at San Jose del Cabo. A small expedition from MJC drove the length of the Baja Peninsula to see the event, one of the great adventures of my life. I didn't get pictures at the time, as the best technology I had was a Kodak Instamatic. The pictures below are from Dr. William Luebke, MJC's retired astronomy professor.
It's going to be a zoo in Oregon in a few weeks, as literally millions of people are converging on the region to have a look at this rare event. We will be staying about an hour's drive from the path of totality, so I have no idea if we'll be able to even get to the dark zone through the gridlocked traffic. If we do, I'll be busy getting pictures to share, and if we don't...well...we'll always have Baja.
Tuesday, August 1, 2017
Liveblogging the Deluge: Is the Big-Boned Lady Singing? The Aftermath of the 2017 Flood on the Tuolumne River
|The Tuolumne in August of 2015. This was a sick river overgrown with invasive hyacinth. Flow is about 200 cfs.|
Goodness sakes, are we still talking about that flood? Well, yes we are. It isn't quite done, although events this week are signaling the end, at least in some respects. In another respect, the five-year drought that we thought the floods put an end to is still with us.
I've had the privilege of seeing two great floods in my time living along the Tuolumne River where it flows into California's Great Valley. The first was the incredible flood of 1997 when the river overwhelmed Don Pedro Reservoir and rampaged through my town at around 70,000 cubic feet per second. The second was this year. The river never topped 15,000 cubic feet per second, but the flood continued for kind of a long time...it lasted for more than six months! The watermaster at Don Pedro Reservoir upstream had to do a delicate dance of balancing the inflow of storm water and snowmelt with a lake that was at more than 95% of capacity. The snow this year was around 200% of normal, and even today, on the first day of August, the inflow is still a respectable 4,000 cubic feet per second. Normal would be a few hundred cfs. I am reasonably sure that I'll never see an event like this again in my life.
|The Tuolumne River in the same spot in January 2017, at about 12,000 cubic feet per second|
After five years of horrific drought, the river channel was in trouble. Without the flushing action of at least a moderate flood, silt had covered many potential nesting sites for salmon and other fish, and invasive hyacinth threatened to choke the channel (the hyacinth crowds out other life and prevents light from penetrating the water; in some places the river was covered entirely by the floating mats).
|The Tuolumne River this morning, at about 1,500 cfs. All of the hyacinth and many trees and willows have been swept away.|
As the river channel starts to emerge from the floodwaters, we can see that trees and willow thickets have been swept away from some areas, leaving a floodplain of barren river cobbles (above). The hyacinth is gone (although I bet seeds are hiding in the soils along the river). In other areas, the floodplain is a tangled mass of trunks, branches and root balls.
The flood took away a lot of habitat for the wide variety of animals that normally live on the floodplain, and took it for a long time (I'm wondering if homeowners on the bluff above had problems this year with raccoons and the like). It will be interesting to see how and when they come back.
For farmers and anyone who uses water, the results are spectacular. Compare where California's major reservoirs were in January of 2015 during the height of the drought to where they are today. It's almost like we have an embarrassment of riches, but not really...
There is one aspect of the drought that cannot be shown on these maps, but which will affect Californians for decades. It's the groundwater. During the drought when surface water was not available, agricultural interests went underground to meet their needs. Paradoxically, almonds became a hot crop, and despite the dry conditions, tens of thousands of acres were planted with the water-hungry trees, and the orchards were almost exclusively irrigated from new wells. After a number of years without subsidence, some areas of the Central Valley began to sink again as the water was pulled out.
The high river flows will contribution a little to the recharge of the groundwater reservoir, but for the most part the water is irreplaceable, and we went through a lot of it. It's analogous to living off of a savings account without making any deposits. In the long run it is unsustainable.