Archive for the ‘other’ Category

Trees and serpentine

29 March 2015

There’s a stretch of Castle Drive, up in the Piedmont Pines neighborhood, lined with huge trees. On the Walk Oakland map, it’s even labeled “Colonnade of Eucalyptus.”


These give me mixed feelings, as tree removal projects have aroused lately elsewhere in Oakland.

First, there’s the experience the trees provide. For one thing, you basically can’t walk here, so the colonnade is not a realistic attraction for walkers. Its main effect is a momentary diversion for drivers, who really don’t need one at this location.

Second, there’s the effect on the surroundings. As you climb up in this valley, the trees emerge as a very tall fence that blocks the view of the hills and the city and the bay.

Third, there’s the geologic setting. This part of the roadway runs along a very steep 40-degree slope through pure serpentinite, visible in the small landslide scar on the right side of the photo. Serpentine rock is poor footing for these massive trees. The trees may seem like they’re buttressing the roadway, but when they inevitably tip over in a storm or earthquake, they’ll uproot it instead, forcing the locals to drive up and down Ascot Drive for many months.

But how about that rock? Here’s a hunk of it that spilled across the road.


And here’s a hand specimen. I love this stone, but roadbuilders don’t.


It’s not my problem, since I don’t live there, but I think the best thing to do is to turn this colonnade into a line of ground-level stumps. The root systems would bolster the soil for another decade or so, giving the city time to plan and execute a properly engineered roadway. And bollards set in the stumps would preserve the trees’ most useful current function of keeping cars out of the canyon.

Trees are supposed to be wonderful stockpiles of carbon, sequestering it from the atmosphere. For me, that argument shouldn’t apply to individual trees or even individual groves of trees. What do we do, in the long run, with the carbon in trees—pile the trunks in pyramids? Carbon is best stored in the soil, where it provides excellent tilth and maintains a thriving ecosystem that resists fire and drought. It’s like circulating money in an economy: do you hoard it in vaults or spread it around among people ready to use it as a medium of exchange? Humans have spent thousands of years degrading the world’s soils, and I’d rather we begin to restore them.

Local global science

16 December 2014


I don’t spend all my time out among Oakland’s rocks. I also take advantage of the Bay area’s opportunities to learn about Earth science. Every year, for instance, I attend the Fall Meeting of the American Geophysical Union, held without fail in San Francisco since 1968. I started in the mid-1980s, and it’s where I’m spending this week. Last year I also started attending the annual sessions of the Cooperative Institute for Dynamic Earth Research, or CIDER, held at Berkeley on the UC campus. It’s a geology geek’s gathering that marked its tenth anniversary last Sunday. UC professor and seismologist Barbara Romanowicz, on the left, is the prime mover; unfortunately I didn’t catch the names of the other two people. CIDER uses an NSF grant to bring together senior researchers and “junior” scientists—grad students and postdocs—who pick a few meaty deep-earth topics and set up a summer workshop to attack them. Last year’s puzzles involved the chemistry of the Earth’s mantle and the nature of the core. This coming year it will be the relation of the solid Earth to climate change, a conversation long overdue among specialists.

Anyway, that meeting was last Sunday and they let me be a fly on the wall. It’s one more thing that makes Oakland the navel of the world.

Claremont chert, and other Oakland rocks, in Sunol

16 November 2014

The other day I took a field trip to see the construction site of the new dam for the Calaveras Reservoir. (The old dam is being replaced because it’s not strong enough to endure a big earthquake on the Calaveras fault, which runs essentially right through it.) It was a cool time, with fossils and big construction vehicles and engineers and grout. As the dam people were orienting us that morning, they passed around specimens of the major rock types in the area, and here was a fine chunk of chert from the Claremont Formation.


The stuff in our Oakland hills is white, because its carbon content was been leached out. This deep specimen retains the organic remains of ancient plankton that make the Claremont, like its larger sibling the Monterey Formation, source rocks for petroleum. (I showed you an exposure of similar stuff down at Alum Rock Park a while back.)

What the heck, I’m not planning to publish these anywhere else: here’s a cobble from a conglomerate down there that’s been stretched and fractured by activity on the Calaveras fault. It was exactly like the examples in our own Oakland Conglomerate.


I think this one was from the Berryessa Formation (which is also found up at Alum Rock). Considering the looseness of the definitions of these formations, I feel safe in correlating them, although Crittenden defined the Berryessa as lying above the Oakland. Anyway, the phenomenon is the same.

One major feature of the construction project is an enormous cut made into the hill on the west side of the dam site. Basically, they discovered an active landslide there and decided to excavate the whole damn thing. We got to wander out along this exposure and hunt for fossils in the Temblor Formation, or at least rocks mapped as the Temblor.


There were a fair number of big ol’ scallop shells to be found, usually in pieces. Also some coaly bits of fossil wood. This is a rare exposure of an actual bedding plane, as marked by a pavement of scallop shells in what looks like their growth position.


We also learned a lot about the recent project that rebuilt part of the Hetch Hetchy Aqueduct that runs through here. Once the work was done, this tunnel-digging machine became surplus.


The guy asked us if we wanted to bid on it. I thought it had the makings of a good Burning Man stunt.


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