Documentary using visual effects to 'drain' the waters from around Alcatraz island, which reveals San Francisco Bay to be a fascinating and chaotic place. On the dry bay floor are scars left by earthquakes, giving scientists an idea of when the next one will strike - and what could happen to San Francisco if one does. Not only that - the draining also reveals why the notorious Alcatraz island prison, which sat in the south of the bay, proved so inescapable