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Science Forum Index » Geology - Earthquakes Forum » Something for Bay Area Geology Enthusiasts
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| Petra |
 Posted: Tue Feb 05, 2008 8:01 pm |
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NORTHERN CALIFORNIA GEOLOGICAL SOCIETY
Wednesday February 27, 2008
Dr. David Morrison, NASA Ames Research Laboratory
Impacts and evolution: astrobiology and near-earth object impacts
7:00 pm at Orinda Masonic Center
Wednesday March 26, 2008 (Date To Be Confirmed)
Dr. John C. Tinsley, US Geological Survey, Menlo Park
Dark holes in Muir's "Range of Light": Insights from southern Sierra
Nevada caves and karst
7:00 pm at Orinda Masonic Center
Thursday March 27, 2007 (Date To Be Confirmed)
(AAPG Distinguished Lecture)
Dr. Peter Skelton, Open University, UK
The Episodic History of Cretaceous Carbonate Platforms: An Aptian Case
Study
1:00 pm at Chevron, San Ramon
Wednesday April 30, 2008
Dr. Leonard Sklar, San Francisco State University, San Francisco
How pebbles destroy mountains: the role of sediment in river incision
into bedrock
7:00 pm at Orinda Masonic Center
Wednesday May 28, 2008
TBA - Likely a Hayward fault talk through the 1868 Alliance
7:00 pm at Orinda Masonic Center
Wednesday June 25, 2008 (Date To Be Confirmed; Likely a Dinner
Meeting)
Dr. David Schwartz, Senior Earthquake Geologist, US Geological Survey,
Menlo Park
Earthquakes in the San Francisco Bay area in the past 2000 years -
commemorating the 140th anniversary of the 1868 Hayward Earthquake
7:00 pm at Orinda Masonic Center
As Usual - Our Summer Break!
Wednesday September 24, 2008
Dr. Rolfe Erickson, California State University, Sonoma
Granites in the Franciscan formation
7:00 pm at Orinda Masonic Center
Wednesday October 29, 2008 (Date To Be Confirmed)
Dr. John Caskey, San Francisco State University, San Francisco
Late Pliocene to Recent stratigraphy and tectonics in the Death Valley
area, California
7:00 pm at Orinda Masonic Center
http://www.ncgeolsoc.org/
The Oakland/Orinda Volcanic's
http://www.baynature.com/2005apriljune/volcanoes.html
Edwards describes Sibley as "a geological museum," and as we walk he
decodes some of the exhibits for me--starting with the basaltic dike
found on Round Top itself. Basalt is the purest form of lava, a hard,
dark, fine-grained material, and a "dike" is the channel feeding the
volcano with molten basalt from deeper in the earth's crust. Here on
Round Top, at the East Bay Municipal Utility District's water tank, we
see a thick dike, perhaps one of the volcano's main arteries, slicing
through a sequence of less homogeneous rock--some of it tuff-breccias,
created by the mixture of volcanic ash, little pieces of lava, and
bits of Orinda Formation gravel all churned together and hardened into
a kind of cassoulet. This material probably sloughed off the interior
walls of the crater and splashed into the water and mud ponding in its
cavity. Over the millennia the mud hardened into a gray mudstone, also
in evidence here. Big basalt boulders lie strewn around the peak.
Weathering turns them a light brownish or rusty-gray color, but
beneath that thin rind they are magnificently dark: "gun steel blue,"
Edwards calls it.
A few minutes later we stand above an old Kaiser Sand and Gravel
quarry. From a geologist's point of view, the decades of digging and
blasting here gilded Sibley's geological lily, providing unique views
into the volcano's heart. "Geologists love quarries, craters, road
cuts, anything that exposes the earth," says Edwards.
At the edge of the quarry pit, a vertiginous spot a quarter-mile
northeast of Round Top, Edwards explains that we are standing near
what would have been the top of the volcano. Here the composition and
shape of the original crater are visible, at least to Edwards. "What
you see in the steep walls across the pit is basalt lava that filled
the top of the crater and ultimately buried the vent," he says. Since
the vent has tilted over on its side, standing at this railing and
looking east is like floating on your back in the original crater. |
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