The tsunami observations produced by the 2018 magnitude 7.5 Palu strike‐slip earthquake challenged the traditional basis underlying tsunami hazard assessments and early warning systems. We analyzed an extraordinary collection of 38 amateur and closed circuit television videos to show that the Palu tsunamis devastated widely separated coastal areas around Palu Bay within a few minutes after the mainshock and included wave periods shorter than 100 s missed by the local tide station. Although rupture models based on teleseismic and geodetic data predict up to 5‐m tsunami runups, they cannot explain the higher surveyed runups nor the tsunami waveforms reconstructed from video footage, suggesting either these underestimate actual seafloor deformation and/or that non‐tectonic sources were involved. Post‐tsunami coastline surveys combined with video evidence and modeled tsunami travel times suggest that submarine landslides contributed to tsunami generation. The video‐based observations have broad implications for tsunami hazard assessments, early warning systems, and risk‐reduction planning.

The eruption of the Hunga Tonga‐Hunga Ha'apai Volcano in January 2022 in the southwest Pacific islands of Tonga triggered a tsunami that was detected beyond the Pacific basin. Here we show its spatiotemporal signature as revealed by hundreds of publicly available coastal tide gauge records from around the world. The Tonga tsunami was characterized by a uniformly small leading wave that arrived earlier than theoretically expected for a tsunami wave freely propagating away from the volcano. In contrast, the largest waves, of up to +3 m high, were concentrated in the Pacific and their timing agrees well with tsunami propagation times from the volcano. While the leading waves were caused by a previously reported fast‐moving atmospheric pressure pulse generated in the volcanic explosion, the large waves observed later in the Pacific were likely originated in the vicinity of the volcano although its generation mechanism(s) cannot be identified by the tide gauge data alone.

Historical records of an earthquake that occurred in 1730 affecting Metropolitan Chile provide essential clues on the source characteristics for the future earthquakes in the region. The earthquake and tsunami of 1730 have been recognized as the largest to occur in Metropolitan Chile since the beginning of written history. The earthquake destroyed buildings along >1000 km of the coast and produced a large tsunami that caused damage as far as Japan. Here its source characteristics are inferred by comparing local tsunami inundations computed from hypothetical earthquakes with varying magnitude and depth, with those inferred from historical observations. It is found that a 600–800 km long rupture involving average slip amounts of 10–14 m (Mw 9.1–9.3) best explains the observed tsunami heights and inundations. This large earthquake magnitude is supported by the 1730 tsunami heights inferred in Japan. The inundation results combined with local uplift reports suggest a southward increase of the slip depth along the rupture zone of the 1730 earthquake. While shallow slip on the area to the north of the 2010 earthquake rupture zone is required to explain the reported inundation, only deeper slip at this area can explain the coastal uplift reports. Since the later earthquakes of the region involved little or no slip at shallow depths, the near‐future earthquakes on Metropolitan Chile could release the shallow slip accumulated since 1730 and thus lead to strong tsunami excitation. Moderate shaking from a shallow earthquake could delay tsunami evacuation for the most populated coastal region of Chile.