Evidence of Mediterranean tsunamis preserved in karst pockets on Malta

The Mediterranean Sea has experienced numerous tsunamis, triggered by earthquakes along the Hellenic and Calabrian arcs, submarine landslides, and volcanic eruptions in Italy and Greece. Nonetheless, patterns related to the timing, frequency, intensity, and dominant triggering mechanisms of these events remain poorly understood. The Maltese archipelago is vulnerable to tsunamis from multiple directions in the surrounding Mediterranean seascape. Malta differs from other Mediterranean coasts because no onshore tsunami-related deposits other than coastal boulders have been reported. However, coastal boulder deposits are difficult to date or link to known events. To fill this gap, our study presents the first identification of sand-grade sediments in northern Malta (L-Aħrax Peninsula) interpreted as tsunami deposits. Found within karst pockets (natural solution hollows in limestone), these shelly sands overlie terra rossa soils and are well-preserved due to the relatively protected nature of the karst hollows. The work provides the first description of tsunami sediments in Malta, characterizing their granulometric properties, sedimentary structures, and micro-faunal assemblages, all indicative of a marine origin. Notably, the presence of the foraminifera Amphistegina lobifera, a species introduced to the Mediterranean after the 1869 opening of the Suez Canal, provides a relative age constraint. The close spatial association of these sands with large coastal boulders supports a tsunami origin. These findings offer the first robust evidence of tsunami deposits in Malta and highlight the utility of karst features in preserving such records. They also expand understanding of tsunami hazards in the Central Mediterranean, with implications for regional coastal risk assessments.