From K-QED. It's a simple but alarming question. If the Lake Chabot Dam in the Oakland Hills

cracked open in a big earthquake, what kind of flooding should the communities below expect?

Are we talking a tsunami knocking down the houses or sidewalk streams.

The question from Holly Ann Vickers-Kang was driven by more than idle curiosity.

She and her husband were considering buying a home in San Leandro, a town right below the dam.

And, you know, we were expecting to see

on the disclosure things about earthquakes,

but I was not expecting to see anything

about a flood zone.

It was totally surprising to me.

She did some research and found the culprit.

Perched in the hills just above town

is Chibboe Dam and roughly 3 billion gallons of water stored behind it in Lake Chabot.

When it was built in the mid-1870s, the dam was one of the largest in the world.

It's a massive earthen embankment about 135 feet high, positioned at the mouth of the canyon where San

Leandro Creek once cascaded from the hills towards San Francisco Bay.

If an old dam holding back billions of gallons of water just

above a densely populated area doesn't scare you, maybe the fact that it was built

within a few hundred yards of the Hayward Fault will.

Scientists say that over the last 900 years the fault has produced a powerful earthquake,

magnitude 6.3 or higher, every century and a half, on average. The last one was a

century and a half ago. That 1868 quake devastated the East Bay caused widespread damage in San Francisco and killed 30 people.

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