This Wed 9/23: A Ramble through Bay Area Caves
Adrian Cotter
SF Bay Area Caves: A Ramble Through the Underground Realm
Guest Speaker: Bruce Rogers
7pm Wednesday, September 23rd, 2015 (doors open 6:30pm)
FREE at the Exploratorium Bay Observatory Gallery (see directions at the bottom for details)
and please let them know if you are coming.
Bruce Rogers will give us a scientist and explorer’s insight into selected caves of the Greater San Francisco Bay Region. The region is not noted for its abundance of known stygian sites, but they aren’t absent. Some you can visit and some you’ll likely never see for yourself, given the restricted access. We’ll include a quick look into the multitude of sea caves (some of national importance); tafoni shelters (a few with fascinating cultural and natural history); unusual caves comparable to only a few other locations world-wide; and even a scattering of small limestone caves and their unique inhabitants. Discussion will also touch on cultural and architectural sites resembling natural caves.
Elephant Bay Entrance, El Reyes Cave
Bruce Rogers began cave exploring in the wilds of New England in 1958. Since then he has explored the basements of North America from the Atlantic to the Pacific and from Alaska to the Guatemala border in addition to many of the island nations of the Pacific Basin. All facets of geology and geography, cartography, photography, and history are included in his spelean interests. Author and/or editor of several books and scores of articles on caves, his current interests are lava tubes, littoral caves, cave history, and Pleistocene fossils in California caves. His interest in speleology led to formal geologic education and to a position as a field geologist at the USGS. There, he also indulged both artistic and scientific bents as a scientific illustrator and web person at the USGS for a third of a century. Since 2007, he has been writing prolifically and is President of the Western Cave Conservancy.
Brenda Goeden of BCDC and Ian Wren SF Bay Keepers joined us on August 19th, 2015 at the Exploratorium to to talk about what gets dredged out of the San Francisco Bay.
Most of the dredging that goes on in the bay is for navigation. This is mostly through mud — 80% of the Bay is fine grain mud, and it is dug out to allow deep draft vessels to come through, and keep waters by marina’s clear. The dredging aka mining of sand is mainly for the construction industry – it becomes cement, asphalt, road-base, sub-base and general fill. The grains of sand are grains (.002 to .08 inches in diameter) bigger than mud, and smaller than gravel. it gets mined on demand, not necessarily day in, day out.
There are two main areas whether the sand comes from: Suisun Bay and the Central Bay. Suisun Bay is a finer grain of sand which is often used for back fill in trenches. The coarser sand of the the Central Bay is used for cement. Sand is only found in the high flow areas of the Bay where the water has enough energy to carry the sand. Mud is taken out to the slow wide sides of the Bay.
Sand is important for a number of reasons outside of its commercial uses — it helps build marshes and beach. It provides shoreline protection as it takes more energy to move, it provides a particular kind of habitat, and on the shore provides a place for recreation and having a place for viewing wildlife.
The amount of historical sand, and sand in the Bay is difficult to measure. Most of the sand in the Bay comes from the Delta and the larger watershed (40% of California’s watershed drains into the Bay), and estimated 1.2million cubic yards, with another 300+ thousand cubic yards coming from local streams. Where not blocked, the rivers and creeks, slide and bounce the sand along into the Bay. Storms and other high flow events are key in moving the sand along and into the Bay and beyond.
READ MORE at
http://sfnhs.com/2015/08/29/dredging-for-sand-in-the-san-francisco-bay/
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