Friday, June 16, 2017
It's the time of year I love the most, our field season, when my students and I hit the road. We are making a grand loop, heading north along the spine of the Cascades, with stops at Mt. Shasta, Lava Beds, Crater Lake (above), St. Helens, and Mt. Rainier. We'll then head across eastern Washington through the Channeled Scablands, and climb into the northern Rocky Mountains at Glacier National Park. From there we'll head south into Yellowstone and Grand Tetons National Parks, and cross the Basin and Range Province on our way back home. Y'all have my permission to let up on the heat wave by the time we come back (stay cool and safe). Needless to say, postings on Geotripper will probably be sparse, but I'll give it a try if I can (maybe the laundromats have Wi-Fi out there).
Sunday, June 11, 2017
|The summit of Mauna Kea in the distance, and the forested lower slopes of Mauna Loa in the foreground|
My last entry on the geological drama of Hawai'i concerned the stubbornness of life in a harsh volcanic environment, such as that which is found on the highest slopes of Mauna Loa and Mauna Kea on the Big Island of Hawai'i. I was echoing of course one of the memorable lines from the movie "Jurassic Park". As I started to review my next set of pictures from my recent trip, I realized the opposite supposition also holds true: rock finds a way (to kill life).
|Lua Manu Crater on Chain of Craters Road. It formed by collapsing several hundred years ago, and was later filled with lava flows in 1974.|
previous post. In 1974, the Keanakāko‘i flow overwhelmed an Ohi'a forest near Chain of Craters Road in Hawai'i Volcanoes National Park. The lava froze around the trunks as the trees themselves caught fire and burned away.
The lava forests can be seen in several places. By far the easiest is at Lava Tree State Monument in the Pahoa area. It resulted from a flow in 1790, and the park offers paved accessible trails and interpretive signs. If you want to see the Keanakāko‘i ghost forest, you'll find it in the vicinity of Lua Manu Crater on Chain of Craters Road in Hawai'i Volcanoes National Park. There are no signs and no trails, so you are in for a bit more of a rugged adventure. Be prepared with water, sturdy shoes, and the other usual things you need for a wilderness outing. And...be careful while studying the ghost trees. Many are unstable and fragile and could be destroyed by a thoughtless climb or push. And having one fall on you can't possibly end well.
|Tuolumne River on Feb. 21, 2017, discharge about 16,000 cubic feet per second|
|Tuolumne River this afternoon, discharge 3,520 cubic feet per second|
And then things got scary. Oroville Dam came uncomfortably close to failure, requiring the evacuation of 200,000 people downstream for a period of time. Don Pedro Dam on the Tuolumne River was not in danger of failure but it came within inches of overflowing uncontrollably, and the emergency floodgates were opened for only the second time in history (the first being in 1997). On January 4, operators at the dam ramped up flows of the river to 10,000-12,000 cubic feet per second (for a day or two, flows reached 16,000 cfs), putting it in a state of official flooding, and the water flows did not begin to recede until only a few days ago. I checked out the river a week back, and the river was down to 6,000 cfs. Today it was 3,520 cfs, and after five months of constant inundation, the floodplain was at long last reemerging. For perspective's sake, the average flow of the river during much of the drought was around 200-500 cubic feet per second.
|On Feb. 21, the river was flowing into the large quarry pond on the top left of the picture.|
|Today, the river and the pond are separated again. The floodplain in the foreground is once again exposed.|
The other changes to consider are the animals. The floodplain was a rich habitat for all manner of mammals, reptiles, amphibians, fish, and creepy crawlers. Many have been displaced for months, and their former homes will be highly altered or gone. There will be large tracts of barren gravel. I'll be watching for their return.
The deluge is not yet over. There is still a huge amount of snow in the high country, and flows will no doubt remain high for weeks or months to come. The full extent of the changes to the floodplain will not be apparent for some time. I'll be there to report when they are!
Friday, June 9, 2017
|Ohi'a Lehua (Metrosideros polymorpha) clinging to a crack in a 1974 lava flow on Kilauea|
|Ohi'a Lehua (Metrosideros polymorpha). The trees are threatened by Rapid Ohia Death disease.|
The Ohi'a is one of the most remarkable tree species on the planet. The Latin name polymorpha ('many shapes') provides a clue why: it can grow in a stunning number of deeply contrasting environments. Ohi'a trees can be found as the first pioneering species on fresh lava flows, as in the pictures above. They can be found on the near-desert leeward slopes of the island's volcanoes. They form the canopy of most of the island's rainforests, growing to heights approaching 100 feet (30 meters). They grow in near alpine conditions at 8,000-9,000 feet on Mauna Loa and Mauna Kea. And stunted trees, barely shrubs, survive in the high altitude bogs on Kauai where the rainfall exceeds 300 inches a year. I know of no other tree species that is capable of such feats.
It's true that you could try and cultivate Ohi'a trees in these kinds of environments elsewhere in the world and they might not do very well in competition with other established species. On Hawai'i, though, all they have to do is survive, because the isolation of the islands has meant that only a handful of other tree species ever arrived. So it is that in the unending battle between rock and life in Hawai'i, the Ohi'a tree is often the main combatant.
The Ohi'a trees aren't entirely alone as colonizers of barren landscapes in Hawai'i. The ʻŌhelo ʻai (Vaccinium reticulatum) is a shrub that can be found on new cinder cones, ash fields, lava flows and alpine slopes. The berry is edible, and is a treat for the nēnē, the native Hawaiian Goose. The geese in fact have a lot to do with spreading the seeds in the inhospitable environments of volcanic landscapes (they leave the seeds in their droppings). I'm trying to think of any other plant or shrub that produces mature fruit when it is only an inch or two high (as in the picture below).
|ʻŌhelo ʻai (Vaccinium reticulatum)|
|Life creeps ever higher towards the barren summit of Mauna Kea|
Sunday, June 4, 2017
|Crystal Springs Reservoir is on the upper left, while San Andreas Reservoir is on the lower right|
It is the geologist's perspective that provides some insight as to the nature of the landscape below. We left from Oakland Airport and flew over the north end of the San Francisco Peninsula, which provided an outstanding view of the San Andreas fault. Often such faults are indicated by linear valleys owing to the ease with which crushed rock in the fault zone erodes. But on the peninsula the fault is even easier to pick out because of the presence of two reservoirs filling the linear valley, Crystal Springs reservoir, and San Andreas reservoir.
We flew out over Half Moon Bay, and soon land was left behind. There was more than 2,000 miles of open ocean ahead of us, a five hour flight. I settled in and thought of how the islands were inaccessible to humans of any kind until only a thousand or so years ago, and even a hundred years ago it took weeks or months to cross the ocean. How even more wondrous the number of bird and insect species that survived the journey over the millennia.
Friday, June 2, 2017
|Pele's Hair collected near the edge of Kilauea Caldera|
First off, the stuff in the first two pictures. These fibers are found around the summit area of Kilauea, and in protected hollows they can accumulate in large masses. It's called Pele's Hair, and it's made of natural volcanic glass, otherwise known as obsidian. Glass is not usually associated with basalt in the minds of most people, but glass can form around any lava that cools so quickly that crystals can't readily form. This odd feature develops around spattering edges of lava lakes like that which currently resides in the crater of Halemaumau. As globs of liquid are thrown into the air, some of the liquid trails behind as a thin fiber, which then breaks off and floats away in the turbulent hot air currents. If you visit the Big Island, you can usually find some near the Jagger Museum on the crater rim.
|Reticulite from Kilauea Caldera|
|Close up of reticulite from Kilauea|
|Keanakāko‘i Tephra partially covered by a 1983 basalt flow.|
It's clear that what we get taught about basaltic lava is not the entire story. Sometimes basalt erupts violently, and as such it can be exceedingly dangerous. An eruption in 1790 killed several hundred Hawaiian warriors on the eve of a major battle, and the event changed Hawaiian history, as the tragedy was seen as the judgment of the gods. These deposits were once thought to be the results of the 1790 eruption, but it turns out that they include dozens of explosive eruptions that took place between about 1500 and the early 1800s.
|Exposures of the Keanakāko‘i Tephra on the margin of the Kilauea Caldera. A 1983 basalt flow can be seen below on the right.|
What caused this explosive activity? In a word: water. When rising magma encounters groundwater, the water can flash to steam, causing intense explosions. Apparently the caldera collapsed to a depth great enough to reach the regional water table, and huge explosions ensued. Something like this happened at Kilauea in 1924 (see the picture below), but the massive explosions totaled only about 1% the volume of the 1790 and earlier eruptions. There have been some seriously dangerous eruptions throughout time on this volcano.
|1924 eruption of Kilauea Caldera, courtesy of the USGS and Bishop Museum|
And that brings us to the strange circles of the mystery. In 1924 some huge blocks were thrown out of Halemaumau crater and were thrown a thousand or more meters. When they landed, they produced bowl-shaped craters. One of the biggest from 1924 weighed 8 tons, and can be seen in the picture below.
The evidence of 300+ years of explosive eruptive activity around Kilauea is sobering. Such eruptions have the potential to do serious damage to surrounding communities around the caldera and in the Puna District to the east. Current research is seeking to better understand the cycle of activity surrounding these periods of violence.