NOAA/WDS Global Tsunami Deposits Database

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Discover where, when and how severely tsunamis affected Earth in geologic history. Information regarding Tsunami Deposits and Proxies for Tsunami Events complements the historical records currently available through the Global Tsunami Database.

Tsunami deposits are the physical evidence left behind when a tsunami impacts a shoreline or affects submarine sediments. These deposits can be preserved in the geologic record and studied long after the tsunami waves dissipate. Tsunami researchers use various criteria to determine whether a deposit was generated by a tsunami. Distinguishing tsunami deposits from storm deposits generates vigorous debate among scientists. Storm deposits often contain fine laminations that are rarely seen in tsunami deposits.

In some cases, the absence of a deposit provides critical information regarding the magnitude of a tsunami. A series of dunes may block the water from a tsunami, preserving the area behind the dunes, while complete destruction is observed where there was no barrier to the tsunami's impact. The estimate of tsunami water height is limited by the height of the dunes.

Criteria commonly used to identify tsunami deposits include:

• sharp, erosive contact with underlying material
• one or more layers of material that fine upward (grain size gets smaller toward the top of the layer)
• layers that thin landward

Tsunami proxies are evidence that indicate an event capable of producing a tsunami occurred, but do not contain direct evidence of a tsunami. Proxies include coseismic subsidence, turbidite deposits, changes in biota following an influx of marine water in a freshwater environment, etc. These data complement the tsunami deposits data by allowing calculation of recurrence intervals of events capable of producing tsunamis.