Saturday, October 3, 2015

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.

Wednesday, September 30, 2015

Yesterday's Mystery Rock Explained (Sort of...)

Yesterday's mystery rock was strange. Had I not been standing on the flanks of the largest volcano in California (and possibly in the lower 48 states), I would have guessed that the rock had been formed by boring (that's as in "digging", not "uninteresting") clams or some other creature. Many of you guessed the same, and I don't blame you at all.
The easy answer, the quickest explanation is to say that this is the surface of a boulder of vesicular basalt, the term "vesicular" referring to the presence of gas bubbles that formed during the extrusion of  lava on the Earth's surface. The boulder was being used as a vehicle barrier at the pullout for the Devil's Homestead lava flow at Lava Beds National Monument. The monument covers a portion of the northern flank of Medicine Lake Highland, a huge volcanic shield complex along the boundary between the Cascade Range and the Modoc Plateau.
The thing is, I've never seen vesicles like this before. They are uniform in size and spacing. They also looked very strange from the side: they were the top of linear tubes running through the rock. I'm not even sure the tubes and vesicles are right side up. The rock had been moved into the parking area, after all, and could have been overturned in the process.
I find references to "pipe vesicles" that form when lava flows over sources of water (the pockets of steam rise through the lava), but I'm not knowledgeable enough on the subject to say that the term applies here. If the volcanologists among you want chime in, I am all ears!
Thanks for the many responses. I love a good mystery!

Tuesday, September 29, 2015

A Little Rock Mystery for the Day

A little rock mystery for the day. What are we looking at, and why is it strange? The picture is about 16 inches across.

"There Can Be Other Occupants" Wait, What? Notes from the Volcano Underworld

Yeah, that's something you want to think about while stumbling around in a dark cave. And for a government sign, that is almost eloquent. I spent the weekend exploring the flanks of the largest volcano in the Cascades, and thus, I assume, in the lower 48 states (all bets are off when we speak of Hawai'i and Alaska). It's called Medicine Lake Highland, and practically no one has ever heard of it. Chances are that it could be the next volcano to erupt in the lower 48, at which time everyone will hear of it. With at least 17 eruptions in the last 12,000 years or so, it has potential.
One of the most unique aspect of Medicine Lake Highland is the prevalence of lava tubes on the mountain. Just one flank of the volcano, preserved as Lava Beds National Monument, has around 700 individual lava tubes with a combined underground distance of more than 75 miles. A cave system within the Giant Crater Flow on the south flank of the volcano can be traced for 14 miles. That's where I was exploring yesterday.
Dot Jean Cave is part of the Giant Crater tube system. Lava tubes form when the lava flow crusts over but the lava continues to flow beneath. The tube system may eventually drain, leaving behind the caves. Dot Jean is easily accessible, just off the National Forest Road 49 a few miles from the summit area. The cave is unique because it doesn't have openings at the lower end. This means that precipitation and cold air can drain into the cave, but can't drain out. Even in summer the ice that accumulates doesn't completely melt away. The ice actually kept me from exploring very far into the cave. There was an ice cascade that would be easy to slip down and very difficult to climb back up.
 It wasn't hard to get to the large ice mass at the top of the slide though, so I made my way down, while watching for the "other occupants" of the cave. What or who on Earth were they hinting at? I guess we were pretty close to Sasquatch country, so I'll figure that's who it is.
The ice mass in the upper part of the cave is large and fairly translucent. It refracts and reflects light from the cave opening above and appears to glow with an eerie blue inner light. It's almost unsettling.
It is strange to walk through a cave that has existed for less than 11,000 years. Medicine Lake Highland is a short of hybrid shield volcano that has erupted a variety of lavas, including basalt, andesite and rhyolite. The most recent eruption was only 900 years ago, and high geothermal gradients and the occasional earthquake swarm indicate that magma still lurks within the mountain. Yes, I did indeed spend some of my time on the mountain this weekend hoping to see an eruption, but no dice. This time.

Sunday, September 27, 2015

Total Lunar Eclipse, Blood Moon...and the World Didn't End

I had a nice perspective on the Blood Moon Lunar Eclipse tonight from my vantage point in the parking lot of the Olive Garden in Redding, California. Mrs. Geotripper tried to be patient when I got up every 15 minutes to go outside and take another picture.
We didn't get to see the beginning of the eclipse out here on the west coast, or at least I didn't as I was driving down the mountain road from Lassen Volcanic National Park, and couldn't see the moon at all until after 8:00 PM. The boundary zone between the Sierra Nevada and Cascades is a rather prominent visual blocker to things on the eastern horizon. But we sure had a nice sunset at Manzanita Lake (see below).
The moon appears red during the highest totality because sunlight is refracted through the Earth's atmosphere and shines across the surface of the Moon. If we had no atmosphere, the Moon would go completely dark during totality. 
Columbus didn't discover that the world was round. That fact was known thousands of years ago from the shape of the Earth's shadow across the face of the Moon. One of my favorite teaching moments took place a few years ago when I asked an earth science class if they could prove that the Earth was spherical. They didn't do all that well ("we have pictures from space!"), so we all went outside and looked at an ongoing lunar eclipse!
The world didn't end (at least not yet). I always get irritated at religious claims about the end times that pop up at moments like this. I'm truly sorry that people can be so gullible about this sort of thing. If one is going to be convinced about their particular religion's claims that the world will end because of a lunar eclipse (or comet, or solar eclipse, or whatever), it's like saying that the sun is predicted to rise tomorrow and therefore the world will end. If a phenomenon is going to be convincing as a sign from God or the gods, then it should be totally unexpected. Like a solar eclipse when the moon is in some other part of the sky. Or the sun coming up in the west. Or planets changing the direction of their orbit. That would be worthy of attention.
This, by the way, is why I wasn't in some place with a view of the eastern horizon. The sunset on Lassen Peak at Manzanita Lake kind of distracted us. A little.

Wednesday, September 23, 2015

Summer Ramblings: The Second Largest Natural Bridge in the United States

It doesn't look so big...yet
As we drift into the last day of Summer (and it's certainly holding on around here, 100 degrees a day ago), I started looking over some of my adventures. There was our Vagabonding on Dangerous Ground in the Pacific Northwest, of course, but I also spent around four weeks exploring the Southwest, and saw incredible things and places. One of those places was Natural Bridges National Monument in Utah, and one of the things was my first hike to the second largest bridge in the United States (and probably the 7th or 10th largest in the world, depending on the strict difference between "natural bridge" and "arch"). Rainbow Bridge in Arizona is the only one that is larger. Number two is in the picture above...can you see it? It doesn't look all that big, does it?
It's called Sipapu Bridge, and it is one of three spectacular bridges in the monument. How big is it? A sense of scale is everything here. Zooming in a bit, one can notice some trees growing in the opening beneath the bridge. 
It's best to see it up close. A trail, said to be 0.6 miles long (I'm skeptical; it felt longer, especially coming back up), climbs down the cliffs to the canyon bottom near the bridge.
The pathway isn't a gentle slope. There are stairways, and ladders are used to surmount some of the short cliffs. Acrophobic people need not apply.
Midway down the canyon, some Ancestral Puebloan ruins provide a brief distraction. The small room above was probably a granary where seeds were stored. The ledge with the ruin offers a nice view of the bridge if you don't feel like going farther down (the bridge has gotten LOTS bigger, and the trail looks MUCH steeper!). I sometimes think the Pueblo people had a nice sense of location.

Those trees we saw under the bridge earlier? It's becoming apparent that we were looking at large mature Cottonwood trees. This opening is huge.
The trail winds down to the base of the bridge, and the span has become otherworldly. Although precise measurements differ a little, the official height of the opening is 220 feet (67 meters), and the width is 268 feet (82 meters). The width at the narrowest point on the bridge is 31 feet (9.5 meters). I'd never seen anything quite like it.
Natural bridges and arches are similar in ultimate appearance because openings in rock are subject to the same physical forces, but the origins of each are different. Bridges form from the direct effect of water erosion as a stream impinges against a narrow ridge where a river loops completely around (meander necks). Arches can result from the erosion and exposure of underground caverns, or from the undercutting of a narrow "fin" or wall of sandstone.
Source: Wikipedia

Sipapu Bridge to me was stunning. I've been to Natural Bridges many times in the past, but we've always taken the shorter trail to the very scenic, but much smaller, Owachomo Bridge (span 180 feet /55 meters, with a height of 106 feet/32 meters). This bridge was something else entirely. So was the hike out, a climb of 600 feet in just over a half mile. It was worth every step!

Tuesday, September 22, 2015

Unusual Sunrise over the Sierra Nevada Today

Sometimes there are just unusual things. I was driving into work early this morning just before the sun broke out over the Sierra Nevada. From my vantage point on the floor of the Great Valley, the rays of the sun were casting shadows on some of the smoke from the horrific wildfires that have afflicted our state in the past few weeks. The sight stopped me in my tracks. The ridge line looks out of focus, but it's not.

The mountains in the picture are probably right about the latitude of Mt. Hoffman and and the Sierra Crest above Tuolumne Meadows. It's a strange and beautiful sight brought about by tragic fires. I'd rather have the homes and forests back. More than 450 square miles have burned in the Sierra and Coast Ranges in the last few weeks.