It's "Where am I Wednesday"!

A glacial valley with rock walls towering thousands of feet above. Waterfalls a thousand feet high. One of John Muir's favorite places.

Challenging cliffs for rock climbers.

So many waterfalls that some are unnamed.

So, where did I spend a good part of my day yesterday?

St. Helens 30th Anniversary

It's the 30th anniversary of the eruption of Mt. St. Helens, the most recent volcanic disaster in the lower 48 states. Aside from the Lassen Peak eruptions of 1914-17, it is only major eruption of the last century, and for us "more mature" folk, the only one in living memory (in Alaska and Hawaii, a way of life...). It was a fascinating event, as most eruptions are, and was a stark reminder that we on the western side of the country are living in a sometimes dangerous place.

Living with volcanoes is like living with earthquakes: we don't know when something will happen, but we should educate ourselves for the eventuality. Volcanic hazards rarely involve Hollywood-style lava: it is the ash that does the damage most of the time, in the form of ash falls, hot ash flows (pyroclastic surges), and lahars (volcanic mudflows of ash and debris).

Don't live around Seattle or Portland? Got no worries? Here in California we have very youthful volcanic features in the eastern Sierra Nevada, in the Imperial Valley near Salton Sea, in the Mojave Desert in several places, in the Basin and Range around Death Valley, in the Coast Ranges, especially north of Napa and Sonoma, and of course around Shasta, Lassen, and Medicine Lake Highland.

Despite the Tommy Lee Jones movie, I don't think Los Angeles really needs to worry about volcanoes though. Stick with earthquakes, floods, landslides and mudflows for the time being!

I'm off today to celebrate St. Helen's 30th by visiting the underside of giant former volcano: Yosemite National Park. Cheers!

Amid the Chaos, the Beauty of an Erupting Volcano

Iceland, Eyjafjallajökull - May 1st and 2nd, 2010 from Sean Stiegemeier on Vimeo.

I hadn't seen this until today (courtesy of Edie at The Little Red Tent, and Americablog), but what a beautiful visual of what's happening at Eyjafjallajökull. It's always a shame when natural events cause serious problems for human society, but volcanoes and other geological processes are also a source of wonder. I don't have much else to say, except great job, Sean!

My Favorite Geology Foto: May's Accretionary Wedge

I was never much of a photographer for most of (some would say "all of") my life. In those olden days when people used this stuff called "film", they would take rolls of 20 or 36 pictures, send them off to a processor, wait two or three weeks, and the pictures would come back in the mail and one could then see the disastrous results of their attempts to capture things on photographic paper. Each image cost money, so every shot had to count.

This had the worst affect during one of the great adventures of my life: a five-week-long hike along the crest of the Sierra Nevada in 1975, just after my high school graduation. We were stretched to the limit on our budget for the trip, so I allocated myself one roll of film per week. That's at best 5 pictures per day, on my little Kodak Instamatic, of one of the most beautiful landscapes on planet Earth. Every shot had to count, so I tried to make sure everything was visible in every picture. As a result, not one of the pictures I took during that 35 day trek is memorable, other than being a memory jogger after 35 years.

So photography wasn't much of my identity or priority as I continued through my career. I used slides in classes, but often from someone else's collection, because I just couldn't capture what I wanted. And it was expensive and I was too impatient to wait for the results.

Then digital happened. I wasn't on top of the revolution, but in 2001 I was making my first overseas geology trip, and I had to have some better way to document the journey to Scotland. I convinced the department to spring for a 3 megapixel Sony point-and-shoot, which arrived the day before our flight left, so by the time I got on the plane, I had shot and downloaded exactly three pictures. Just the same, the freedom to take hundreds of pictures was a breath-taking revelation. I could concentrate on single subjects! I could use the macro setting to take close-ups! And best of all, I could erase the many rejects without a financial implication!

So now I have a digital library of around 30,000 pictures of mostly geologic topics (not to mention the additional thousands of family pictures) and Chris at Highly Allochthonous is deviously asking us to chose our favorite photo for this month's Accretionary Wedge Carnival. I had a hard time choosing, and on another day another picture would probably be chosen, but my pick is the shot above, looking through an arch at Arches National Park towards the La Sal Mountains in Utah. Why did I choose it? I think it is because it is a single shot that actually does capture the essense and expanse of geology (in other words, it does what all my Sierra pictures in 1975 were supposed to do).

The Entrada Sandstone framing the picture is a Jurassic dune and coastal estuary/mudflat deposit. Dinosaurs and other wondrous creatures lived and died on these sands. The La Sal Mountains in the distance are cored by laccoliths, large mushroom shaped intrusions that were probably magma chambers for long vanished volcanoes. The tilted rocks in the foreground are the part of a large anticline, an upward pointed fold in the crust that was pushed up by huge masses of salt that pushed upwards and pierced the crust. As the salt breached the surface, it dissolved away and the top of the anticline collapsed inwards. The overlying sandstone cracked into numerous wall-like fins. Weathering ate away at the glue holding the sandstone together at the base of the fin, and wind and water carried the sand away, leading to the formation of an arch. So, in one picture we have volcanism, plutonism, erosion, deposition, paleontology, tectonism, and...memories, because Arches is one my favorite places on the planet.

Moderate Earthquake in Puerto Rico

A moderate earthquake has rocked Puerto Rico, with a magnitude of 5.7 (now 5.8 after USGS review) and depth of 110 kilometers. At that depth, I don't think there is much potential for damage, but local residents are no doubt concerned about feeling any shaking after the tragedy of Haiti. Like Haiti, Puerto Rico sits uncomfortably close to a major plate boundary, and there is a history of damaging quakes in the vicinity, especially in 1670, 1787 (possibly a magnitude 8.0), 1867 (magnitude 7.5) and 1918 (magnitude 7.5). The 1918 event caused a 19 foot high tsunami, and 112 people were killed. More information about the hazards of this part of the Caribbean Sea can be found here.

UPDATE: The quake was widely felt in PR, and caused minor damage, mostly cracked walls and several rock falls on roads: info here (in Spanish)

Red Hills Redux

In late March, I paid an early spring visit to a unique geologic locale in the Mother Lode of the Sierra Nevada, the Red Hills Area of Critical Environmental Concern, which is such a better moniker than such things as "park" or "wilderness". So much easier to say or write! It was an ideal example of the "Other California", those places that never seem to show up on the postcards. At the time, we were enjoying the early blooms of the many endemic and unusual flower species growing on a serpentine soil that prevents the usual grasses and oak trees from flourishing.

It was an uneventful afternoon of an uneventful week, so we hopped in the car and drove back up Highway 132 towards Chinese Camp to see if any of the flowers were still there six weeks later. Things were certainly drying up, but plenty of flowers were still blooming along the small creeks.

There was still a lot of daylight left, so we figured why not head up towards the high country and figure out was blooming up there? So we jumped onto Highway 120 towards Yosemite National Park. As tempting as it was, by the time we reached the Rim of the World Overlook, it was nearing 6:00 PM, and Yosemite itself was out of the question (that trip will have to wait a few days).

The Rim of the World Overlook provides a rather spectacular view into the vast gorge of the Tuolumne River, which cuts into the westward tilting block of the Sierra Nevada province. The Tuolumne had the longest glaciers during the ice ages, but they never reached this far. This is a river-carved canyon.

The two forks of the Tuolumne meet below the view point some 1,500 feet below, but the rivers could be clearly heard. The viewpoint lies very close to the boundary between the granites of the Sierra Nevada batholith and the early Paleozoic metamorphic rocks of the Shoofly Complex, one of the oldest rocks found anywhere in the Sierra Nevada.

By the way, yes, there were a great many flowers to be seen at the 3,000 foot level of the Sierra. The highway was bedecked in many places with purple and white lupine, with the occasional splashes of red Indian Paintbrush. The scene below was just off the upper end of Ferreti Road, which winds through a resort complex at Pine Lake near Groveland.

We capped off the evening with a nice selection of Mexican cuisine at Alfredo's in Sonora, a small restaurant that I recommend!

Friday's Fun Fotos: the Fluvial Forest Discussed

I posted some pictures of a "fluvial forest" this morning (fluvial=river) asking for an explanation about how these trees came to exposed in the river channel, and in short order got three excellent answers. I've provided a larger format picture above to give some perspective on the setting (click on the image to see the bigger picture). This is the West Walker River, a few miles downstream from the junction of Highway 395 and Highway 108 from Sonora Pass in California's Sierra Nevada.

It's rather striking and strange to see so many trunks of mature trees sitting in the active channel, as Jeffrey pine really can't tolerate soaking for more than a few weeks a year. They otherwise do quite well on the shady slopes to the right in the picture above (and not so well on the dry slopes to the left). I have to admit that this was my thesis area, but I didn't really give the trees much thought 25 years ago, yet they reveal an interesting story.

Anne had a great idea, saying that mining wastes could have caused the filling of the channel, smothering the trees. This would be a great explanation, and such a thing indeed happened in the Sierra Nevada during the hydraulic mining era of the Gold Rush (I posted a picture of a tree trunk formed this way some time back). The problem is that no mines of any consequence were present in the area.

Rob provides a glacial explanation, in which glacial outwash buries a forest, and then a surging glacier planes off the trunks. This is an appealing explanation because this part of the canyon was very close to the terminus of the Tioga and Tahoe glaciers. Glaciers would explain it, except the age of the trees are wrong. One set of the trees in this fluvial forest grew between AD 900 and 1100, while another set grew between AD 1210 and 1350. Smaller glacial episodes in the last two thousand years never approached the area.

Lockwood comes the closest to explaining what happened here, suggesting that a debris flow filled part of the canyon, killing and burying the trees, and then the river exhumed the forest. But there is an interesting twist: the valley is really narrow here (look at the top photo; there is barely enough room for the river and the highway, and when the river floods, there is no room for the highway at all. It disappears and has to be rebuilt, most recently in 1997). The trees, and there are dozens of them, were pretty much filling the entire canyon bottom. There was almost no room for a river channel when these trees were growing. This suggests that the river was much smaller in the two time periods the trees represent. In other words there were two crippling droughts that lasted 200 and 140 years respectively. Once the droughts ended, the river filled the channel with sediment again, and debris flows, as Lockwood suggests, undoubtedly had a role. Outwash from the Matthes glaciation may have been a factor as well.

There is confirming evidence for such mega-droughts in other areas of the Sierra Nevada. Tenaya Lake, Lake Tahoe, and Fallen Leaf Lake all have submerged forests that grew to maturity during these periods when the lakes didn't have enough water to breach their outlets. Oral histories of California's Native Americans also hint at terrible droughts.

In human time frames, droughts are a fact of life here in California. We had extended droughts from 1928-1934, 1960-61, 1976-77, and 1988-92. We may or may not be ending a three year drought this year as well. Our population has grown so large that each drought becomes more problematic, and we muddle through on the strength of a few extraordinary precipitation years that fill reservoirs for a time. What would we do if another century-long drought were to come? And what role will anthropogenic global warming play? I, for one, wouldn't particularly care, because I will be dead, but my grandchildren might have a real struggle.

Stine, S., 1994. Extreme and persistent drought in California and Patagonia during mediaeval time. Nature 369:546-549. I can't find a copy of Stine's paper on the web, but Stine's findings are discussed briefly here (page 15-16), and here (page 296)