Post 500

9 October 2017

The experts say the greenhouse gases we’ve put in the atmosphere will affect global climate for the next several centuries. Where will we be 500 years from now, once this pulse of carbon dioxide has been drawn down by the seas and soil? What will the post 500 world look like?

I’m fond of talking about the deep present, the idea that we should run society as if any natural event that’s happened during the last 10,000 years or so, not just recorded history, could happen again tomorrow. But for the greenhouse pulse the deep present is no guide, because the world hasn’t seen its like for millions of years. The greenhouse pulse has shoved us into the Anthropocene age in which, like it or not, humans are a large-scale geological force.

The Anthropocene world will be an ad hoc world. Post 500, the sea will be tens of meters higher than today, but once we have the means to regulate the climate I suspect we’ll keep the sea where it is, for stability’s sake. I don’t see us bringing the glaciers back unless there’s an existential need.

Some aspects of the future are sure things. I am sure we’ll still be scrambling to deal with the damages we’ve done to the natural world we inherited: the ruined aquifers, the risen seas, the climate out of equilibrium, the ecosystems lost or knocked askew by extinctions and invasives, the metal ores depleted, the billions of holes we’ve made in the ground.

It’s harder to imagine the state of human society post 500. Look back 500 years to 1517 — the Portuguese empire was pushing into the Spice Islands and the Magellan expedition, the first to circle the globe, was still being organized in Spain. Modern science was many generations ahead.

It makes me uneasy to say this, but unless the human population can be reduced to Earth’s carrying capacity, perhaps one-tenth its present total, we’ll need to engineer fully artificial living arrangements that don’t affect the rest of creation. If you like, call that a zoo for humans. If you like, call it the terrestrial version of a Moon base. It will have to be so good we’ll want to live that way. We’re already getting there.

We will need to minimize our wasteful, precarious agricultural system based on pesticides, fertilizer and soil. To save the world’s plants and animals from widespread extinction we will need to stop encroaching upon their environment — not just stop, but withdraw.

Surely the post 500 world will differ wildly from ours. But the seeds of that world are sprouting today. In the past 500 years we have mastered matter, and in the next 500 I anticipate that we’ll master biology and recycling. We will no longer use fossil fuels, and we’ll do much less mining on Earth than today, if any. We’ll undam most of the rivers and heal the coral reefs.

Why do I bring up all this in a blog on the geology of Oakland? Because we’re building the post 500 world now. Look at the 50 years just past, and imagine that degree of change and progress over the 50 years to come — even as sea-level rise starts to really kick in. The next 50 years is the first one-tenth of the next 500 years, and the most important part. Progress will require knowledge of the Earth and the confidence to apply it. Thus Earth scientists will be central as we make our way.

And Oakland will endure; it’s too important not to. Mass transit will gain ground as population density increases. As the sea rises, we’ll raise our harbor and airport and rail lines, even if they end up on plateaus. We’ll restore the salmon run up San Leandro Creek, and our building stock will improve as we go through repeated earthquakes, rebuilding higher each time.

Those are sure things, and they can be done right if we insist. What matters is our culture. What we do today, and how we do it, will make all the difference on our way to post 500, the year 2517.

(Yes, this is my 500th post.)


Twenty Oakland rock types in a 30-mile drive

2 October 2017

As far as I can tell, Oakland has more rock types within its boundaries than any other city in America. When I added them up for a talk I gave at East Bay Nerd Nite, I counted more than 25, from limestone to blueschist. This 30-mile road trip will take you to most of them, with the Hayward fault as a bonus. It starts above the UC Berkeley campus and runs south the length of the high hills, then goes back north through Montclair and Piedmont to end at Mountain View Cemetery.

That’s 1200 pixels wide if you click on it, but don’t worry, I’ll show it in pieces below for more detail. In fact, let’s go to part 1 right now. It goes from Grizzly Peak through Joaquin Miller Park on Grizzly Peak and Skyline Boulevards.

The numbered segments correspond to the formations on the geologic map, as follows:

  1. Moraga Formation (basalt, andesite, tuff)
  2. Orinda Formation (conglomerate)
  3. Claremont Shale (chert, shale, dolomite limestone)
  4. Sobrante Formation (mudstone, shale)
  5. Unnamed mudstone/sandstone
  6. Redwood Canyon Formation (sandstone, siltstone)
  7. Shephard Creek Formation (sandstone, mudstone, siltstone, shale)
  8. Oakland Conglomerate* (conglomerate, sandstone)
  9. Joaquin Miller Formation (sandstone, shale)

Then there’s part 2, from Joaquin Miller Park to the edge of Montclair on Skyline, Grass Valley Road, Golf Links Road, Keller Avenue, Campus Drive and Redwood Road.

  1. Serpentine (serpentinite, blueschist)
  2. Oakland Conglomerate* (conglomerate, sandstone)
  3. Knoxville Formation (conglomerate, shale)
  4. Leona volcanics (metatuff, metabasalt)

Part 3 takes the freeway to Montclair Village, where you won’t see any rocks, then goes down Moraga Road to Piedmont’s Dracena Park and over to Mountain View Cemetery, where rocks are abundant.

  1. No rocks to be seen, but do stop on Medau Place and spot the offset curbs where the Hayward fault crosses it
  2. Franciscan melange (argillite, metachert, greenstone)
  3. Franciscan sandstone (sandstone, siltstone)
  4. Franciscan melange

The cemetery’s melange has many bodies of hard rock (knockers) that stand above the ground. They have their own blog category. Search this site, or check the category list on the right, for posts I’ve written about these rock units.

*The cobbles embedded in the Oakland Conglomerate offer more rock types, including granite, quartzite, gneiss and schist. That’s how I get up to 20.

The highest point in Oakland

25 September 2017

I have believed — and what’s worse, repeated — that Oakland’s highest point is Grizzly Peak. In fact, the highest point within the city limits is Chaparral Peak, an eminence so subtle you can barely tell it’s there.

Let’s look at the 1959 topo map of the high Berkeley Hills. Everything south of the county line is in Oakland.

Grizzly Peak stands out, at approximately 1745 feet. Figures differ, so don’t quote me on that. But Chaparral Peak definitely rises above the 1760 foot contour, making it a hair over one-third of a mile above the Bay. Here’s the mountaintop, such as it is.

It’s Oakland’s largest exposure of the Bald Peak Basalt, which extends from here beyond Vollmer Peak.

Chaparral Peak is the heart of Frowning Ridge, a name we don’t use much (and I’m not sure we ever did). Frowning Ridge is an ill-defined set of peaks and eminences running from Grizzly Peak to Chaparral Peak and then down Siesta Valley where it’s cut off by a fault. This is the view upridge to Grizzly Peak. Mount Tam is in back, on the left.

And this is the view southeast to the Oakland Hills.

Round Top is in the center, against the sky, and exactly in front of it is 1684 Hill. On the right rises a nameless hill, topped by a large installation, where the county line goes. I think of these as affiliated with Gudde Ridge, on the south side of Route 24, because they line up with it.

Both ridges reflect the presence of volcanic rock units. Frowning Ridge is held up by the Bald Peak Basalt and Gudde Ridge (and its northern affiliates) by the Moraga Formation.

Here’s one more view, this time due east across the far flank of Siesta Valley to Mount Diablo.

The Mount Diablo Base Line, the master line for land surveys in most of northern California and all of Nevada, runs right between Chapparal and Grizzly Peaks. That’s the red line on the map, with Township 1 North and 1 South on either side of it.

Sibley sights: Lapilli tuff

18 September 2017

Sibley Volcanic Regional Preserve is the site of a small volcanic center that was last active about 10 million years ago. After it fizzled out, the whole thing was gradually buried in younger sediment. Within the last few million years, the action of the Hayward fault squeezed, folded and uplifted this sequence of rocks and tilted it almost to perpendicular. Then erosion of the uplifted hills — and quarrying by a Kaiser company — exposed a good cross section to view.

Stop number 10 on the self-guided geology tour is an out-of-the-way spot where a rare and striking example of lapilli tuff is exposed. Each time I pass by — three times so far — I can’t resist photographing it. There was May 2005:

There was June 2009:

And there was just last month.

I need to unpack the name “lapilli tuff.” Tuff is a rock type consisting of ash — volcanic material that’s been explosively erupted and then lithified. It’s formally called volcaniclastic material: pulverized rather than solid lava. Lapilli is the name for ash particles of the same size range as gravel, or 2 to 64 millimeters across.

These lapilli (a single particle is called a lapillus) are very consistent in size and texture. They suggest that a spray of red-hot lava was erupted from a volcanic vent nearby and fell together in a neat pile. Perhaps there were strong winds at the time that sorted the droplets by size. Whether the lapilli were still so hot that they fused together before they fully cooled — an agglutinate — or fused together later when cold — an agglomerate — is not clear to me.

Whatever the circumstances were, they were unusual enough that only wide-ranging geologists and professional volcanologists are likely to have seen more than one example of rock quite like this. It merits the specialized name lapillistone, because it appears to contain very little material other than lapilli.

Oddly, it seems I never photographed the same rock twice during my visits to this spot, although it’s possible the rocks eroded beyond recognition over that 12-year span. Will have to keep coming back.