November 21, 1910 Tsunami: San Francisco, CA, United States

A quiet morning with light winds was suddenly interrupted by a rapid fall and then rapid rise in barometric pressure. Marigram records displayed unusual markings, first thought of as the possible result of a submarine disturbance. The water rose more than a foot, fell, and then fluctuated. Present knowledge has us regard the disturbance as atmospheric rather than submarine, and to assume that the water simply responded to the sudden and violent change in air pressure. There was a large storm in the vicinity of Washington and British Columbia, which weather observers believe spawned this pulse. Apparently, atmospheric gravity waves can be set up meteorologically and travel considerable distances from their source. This event is an important illustration of how meteorological effects can create marigrams which look convincingly like tsunami records without accompanying storms. Listed as validity 0, which is defined as “Date is proven to be in error; source of water disturbance is known to be from a meteorological or an astronomic tide source; reported tsunami effects shown to be in error in later documents which are based on primary references” (Reference #237).

The tide gauge at San Francisco registered waves of the tsunami type of meteorological origin, hypothetically caused by a rapid drop in pressure of 2 mm (0.1 inches) from 4:00 to 5:00 (local time, 12:00-13:00 UTC) and a rapid rise by the same amount from 5:00 to 6:00 (local time, 13:00-14:00 UTC). LIsted as definite tsunami. (Reference #415).

Reference #12345 lists as validity 3 or probable tsunami