Archive for the ‘oakland hazards’ Category

Our slides

26 March 2014

A large, deadly landslide in northern Washington has been making news. Smaller ones around here aren’t deadly, thank goodness, but they are sneaky and expensive and everywhere.

slidescarp

This isn’t a landslide yet, but these concentric cracks in Skyline Boulevard are typical signs of slumping ground. A city with more money to maintain streets would have dribbled tar over these cracks when they first appeared, a year or two ago. As it is, each crack lets rainwater into the hillside where it promotes more slumping. Keeping the road sealed will buy a few years’ time.

This location is underlain by the same incompetent Sobrante Formation that gave the Caldecott Tunnel builders such trouble. But landslides occur in Oakland on nearly every geologic unit, from the lower streambanks to the highest hills.

The Kitchener scarp

30 November 2013

The recent walk by the Oakland Urban Paths group took us past a catastrophe I hadn’t seen before: the landslide of 15 January 1970. It removed nearly all the homes on the east side of Kitchener Court, just south of the LDS Temple, and dumped the ground into the valley of upper Peralta Creek. The land is still empty and uninhabitable. Here’s a look south over the scarp from Kitchener.

kitchenerscarp

The slide wiped out the middle of London Road between a tiny stub at the top of Maple Street and the forlorn end trailing off of Maiden Lane. The Hayward fault is mapped right through the foot of the slide. The site of my photo is across the pink strip opposite the “J” on this portion of the Oakland geologic map.

kitchenergeomap

I frankly can’t vouch for any of the bedrock divisions shown here, but the dashed line of the fault is close enough to reality. For orientation, here’s the equivalent area in Google Maps. Rettig canyon, where Peralta Creek cuts through the bedrock ridge of Leona keratophyre (pink) and mixed Franciscan rocks (KJf), is in the patch of green at lower center.

kitchenergoogmap


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