The image below is a view south from the Marin Headlands towards San Francisco’s western shore. The building perched on the edge of the Golden Gate, near the photo’s center, is the Cliff House, and behind it, to its right in the photo, Ocean Beach stretches south. At the southern end of Ocean Beach lies Fort Funston, and just to the right of Fort Funston’s orange cliff, a mile or two further south, one can see what geologists term a ‘horse’.

This particular horse is a product of movement on the San Andreas fault: one side of the fault has been thrust north, into the ocean. Daly City sits perched unsteadily atop the northern lip of the San Andreas’ rift. I live at the foot of this ridge in the Sunset District of San Francisco, below Daly City and just above the Cliff House in the photo.

The prominent ridge behind the San Andreas’ valley is Montara mountain, part of the Salinian block. The Salinian block is a fragment containing Sierra Nevadan granite that has moved several hundred miles north along the San Andreas.

Click to enlarge

The wikipedia entries earthrise, the blue marble, and pale blue dot are pretty good at giving the significance of photos of earth from various NASA missions.

The photographs provided humanity with an epiphany equivalent to revelations such as Darwin’s theory of evolution, the Alvarez team’s discovery of an iridium layer at the K/T boundary (and comet Shoemaker-Levy’s subsequent impact on Jupiter), and Hutton’s observation of deep time, as revealed in the Jedburgh unconformity.

For the first time, we had not merely an abstract understanding of the scale of our planet; rather, we also had photographs that showed the planet in the context of its local environment.

Earthrise

The blue marble

Pale blue dot

NOAA Paleoclimatology slide sets.

Via Highly Allochthonous, a nice explanation of crossbedding.

Mantleplumes.org

The debate about whether plumes exist or not, and what other mechanisms could cause melt anomalies became increasingly popularised in late 2002 and early 2003, as observations conflicting with the plume hypothesis, or unexpectedly failing to confirm it, reached proportions that could no longer be ignored. Journalists began to take notice and write popular articles about the controversy. However, there was almost nothing on the world wide web about the subject. Thus, www.mantleplumes.org was born in March 2003.

I decided to look around for open source scientific journals after remarking to a friend about how sad it was that scientific and intellectual inquiry in the U.S.

was being stymied by irrational patents, excessive copyright lengths, and oligopolies. I found the Directory of Open Access Journals. I know also of the Public Library of Science.

As reported in the San Francisco Chronicle, a die-off of plankton has occurred in the waters off of Washington, Oregon, and California due to a cessation of upwelling of cold waters. From the Chronicle article:

“Things are pretty grim up here,” said Bill Peterson, an oceanographer with the National Marine Fisheries Service office in Newport, Ore.

Peterson said a major die-off of double-crested cormorants recently occurred in Oregon, and juvenile salmon numbers have dropped precipitously. Both events, he said, are likely due to the warm water.

“We do salmon surveys every spring and summer,” he said. “Normally, we catch several hundred salmon in the spring. This year we caught eight. And we usually get several thousand fish in the summer. This year, it was 80.”

Peterson said the water temperature off Oregon in late June is normally 10 degrees Celsius (about 50 Fahrenheit), “and this year it’s 16 degrees (about 61 F). Our (upper layer of warm water) is normally 15 meters thick, and this year it’s 30 meters. Krill numbers are down, and the plankton we are seeing are as unusual as can be — warm water species that you’d find off San Diego or Monterey.”

Peterson said it is unlikely Oregon waters will cool significantly this summer.

“It takes an enormous amount of (offshore wind) energy to push that much warm water offshore, which is what we would need to see for significant upwelling,” he said. “I don’t see that happening anytime soon.”

Franciscan Cherts of Marin, a page from the Marin College’s To See a World project, looks like it offers a good exploration of the geology of the Marin Headlands (excerpted below).

It is part of the To See a World project’s “Geology of California’s Golden Gate: A Virtual Field Trip” site.

Of particular interest to me is the Baker Beach field trip, given that I live nearby.

These rocks, like the pillow lavas they cover, clearly formed underwater, definitely in very deep water, possibly at the Equator and during the age of dinosaurs (Marin’s wet Jurassic Park?). This is an image of an exposure of these ribbon cherts in the Marin Headlands. A example of a modern environment in which the majority of Marin’s cherts were formed is seen in this seismic profile collected during the voyage of the USNS Kane in 1968.

Microscopic radiolarian skeletons, are today, forming extensive sediments in the Equatorial regions - they seem to like warm water and thrive in the nutrient rich Equatorial upwelling region. Radiolarians are protozoans which form skeletons of glass (SiO2). Their skeletons are quite well preserved within the hard chert, even though there has been extensive alterations of the originally soft oozes they comprise. This scanning electron micrograph of a radiolarian actually comes from similar-aged limestones in the San Andreas Fault zone near Olema.

Some cherts resting immediately upon the pillows, have been significantly metamorphosed by hot seawater and converted into “pretty chert” or “jasper”. This photo shows a thermal front within chert in close proximity

to highly altered pillow lavas. The cherts close to the pillow lavas commonly have significant accumulations of metallic oxides within them, commonly manganese within Marin, but some small amounts of copper have been mined from the western slopes of Mt. Tamalpais. This photo shows interbedded manganese and chert from Red Rock Island in San Francisco Bay. All of these metallic deposits are likely ancient “black smoker” deposits, like those reported photographed from the East Pacific Rise where it enters the Gulf of California (see pillow lava page) and in the Gorda Ridge off of Northern California and Oregon.

While Ring Mountain it self does not have any good chert exposures, there happens to be abundant chert on the top of Ring Mountain. This chert was imported for the construction of the Nike missle site that occupied the ridge during early parts of the cold war.

Excellent…I’d actually like to take one of the “Field courses that feature the geology of the Pt Reyes Peninsula
and Eastern Marin … offered regularly by the College of Marin.”

USGS table of epochs.

Wandering about more in a completely casual, amateurish way, I found a rather interesting citation. It says, in short, that an Antarctic meltwater pulse at the end of the last ice age strengthened North Atlantic Deep Water (NADW) formation, thereby warming the North Atlantic, which caused a pulse of meltwater from the Laurentide and Fennoscandian ice sheets, which then shut down the NADW, thus causing the Younger Dryas. Got that?

The Younger Dryas is an anomalous 1300 year cold snap just after the end of the last ice age. It seems to have begun and ended with astonishing rapidity, and involved a 7 degree C temperature drop globally in as little as 20 years. Essentially, the world emerged from the last ice age briefly, and then snapped back into and out of it.

Oh, the Bolling-Allerod of this entry’s title is the interstadial (that is, warm period) that ended the last ice age.

Here’s the cite (It’s from PubMed, here):

1: Science. 2003 Mar 14;299(5613):1709-13. Related Articles, Links

Comment in:

* Science. 2003 Mar 14;299(5613):1645.

Click here to read
Meltwater pulse 1A from Antarctica as a trigger of the Bolling-Allerod warm interval.

Weaver AJ, Saenko OA, Clark PU, Mitrovica JX.

School of Earth and Ocean Sciences, University of Victoria, Post Office Box 3055, Victoria, British Columbia V8W 3P6, Canada. weaver@uvic.ca

Meltwater pulse 1A (mwp-1A) was a prominent feature of the last deglaciation, which led to a sea-level rise of approximately 20 meters in less than 500 years. Concurrent with mwp-1A was the onset of the Bolling-Allerod interstadial event (14,600 years before the present), which marked the termination of the last glacial period. Previous studies have been unable to reconcile a warm Northern Hemisphere with mwp-1A originating from the Laurentide or Fennoscandian ice sheets. With the use of a climate model of intermediate complexity, we demonstrate that with mwp-1A originating from the Antarctic Ice Sheet, consistent with recent sea-level fingerprinting inferences, the strength of North Atlantic Deep Water (NADW) formation increases, thereby warming the North Atlantic region and providing an explanation for the onset of the Bolling-Allerod warm interval. The established mode of active NADW formation is then able to respond to subsequent freshwater forcing from the Laurentide and Fennoscandian ice sheets, setting the stage for the Younger Dryas cold period.

PMID: 12637739 [PubMed]

Ah, disaster: it’s so much fun. I’ve long had an interest in geology, and that led in turn to related areas, such as glaciology, paleoclimatology, and the like.

Vredefort dome, South Africa
Space shuttle image STS51I-33-56AA

I just watched the movie, The Day After Tomorrow, and following that I was browsing the net, checking out what has been found in the attempt to piece together the transition from the last ice age to this most recent of interregnums, our warm period, the Holocene. And of course one finds on the net plenty of scientific information, but also a plethora of wacky obssession with doomsday scenarios. It’s a curious propensity, this fascination with events approaching from the periphery of human consciousness and memory. Shadows from beneath the bed.

The biggest local cosmic train wreck so far? The Vredefort dome.

Where else would one find descriptions as colorful as this (from the link above):

This ring of hills comprises quartz conglomerates as found in the gold-bearing strata of the Witwatersrand reefs.

Village, Vredefort dome, South Africa

Village stones, Vredefort dome, South Africa

Photos from
Hartebeesthoek Radio Astronomy Observatory

The white quartz pebbles are evident. This was once the bed of a fast flowing water course which
deposited grains of quartz and the pebbles. This area was mined for gold in the 1880’s. However the concentration of gold was much poorer than at Johannesburg, and the diggings were soon abandoned. Old mine adits are still to be seen in the hills. This is the Amazon Reef.

The outermost ring of hills was home to a quite different group of people in the 1500’s to 1700’s. These were SeSotho/SeTswana-speaking farmers. This village at Askoppies was a defensive position on the crest of the hill, but it did not save the village from destruction, by the warriors of Mzilikazi. The view shown above left looks east, back in towards the inner rings of the Vredefort dome.

The stone walls of the village are shown above right. They are made of the fine-grained grey Ventersdorp lavas that comprise this ridge. These rocks are 2700 million years old.

of illustrative climate-change related charts is here (I’ll try to include attributions later, but most are from the excellent American Scientist article cited in the graph caption, below).

My favorite of these? The chart that shows anthropogenic induced change in the atmospheric concentration of C02. The two graphs shown are derived from an ice core from Vostok, Antarctica. The top chart is of deuterium, a proxy for temperature. The bottom is of CO2, parts per million. The time scale at the bottom is in thousands of years before the present.

Vostok Ice Core, Antarctica, 0 to 160,000 years before present
Top chart is deuterium (per mil).
Bottom chart is C02 (parts per million by volume).

Graphic from “Rapid Climate Change,” Kendrick Taylor,
American Scientist, July-August, 1999.

The Holocene is the 10,000 or so year-long warm period that we’re living in now. The cold stretch of 125,000 years prior to the Holocene is the most recent Pleistocene era glaciation, know as the Wisconsin ice age in North America. Just before the Wisconsinin is the Eemian, another brief warm spell like our own; and before that lies an earlier glacial period (but still lying within the 2 million year extent of the Pleistocene). The red spike on the left side, bottom chart is the increase in atmospheric C02 caused by humans in the industrial era, now 150 years old.

I’ve been reading a little more about the Younger Dryas, which was an abrupt state change in climate, probably global in scale, from warm back to cold, lasting for about 1300 years, and ending 11640 years before present. This AGU page describes the event:

The Younger Dryas (YD) was the most significant rapid climate change event that occurred during the last deglaciation of the North Atlantic region. Previous ice core studies have focused on the abrupt termination of this event [ Dansgaard et al., 1989] because this transition marks the end of the last major climate reorganization during the deglaciation. Most recently the YD has been redated–using precision, subannually resolved, multivariate measurements from the GISP2 core–as an event of 1300 +/- 70 years duration that terminated abruptly, as evidenced by an 7C rise in temperature and a twofold increase in accumulation rate, at 11.64 kyr BP [ Alley et al., 1993] (Figure 2). The transition into the Preboreal (PB), the PB/YD transition, and the YD/Holocene transition were all remarkably fast, each occurring over a period of a decade or so [ Alley et al., 1993]. Fluctuations in the electrical conductivity of GISP2 ice on the scale of <5-20 years have been used to reveal rapid changes in the dust content of the atmosphere during the same periods and throughout the last glacial [ Taylor et al., 1993b]. These rapid changes appear to reflect a type of “flickering” between preferred states of the atmosphere [ Taylor et al., 1993b], which provides a new view of climate change. Holocene climates are by comparison stable and warm.