Farming triggered medieval tsunamis at Italian lake, raising current risk
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In 1117 and 1222, earthquakes at Lake Iseo in northern Italy caused tsunamis after sediment collapses from the lake’s delta. Researchers connected these collapses to centuries of farming and forest clearing in the surrounding Val Camonica valley, which increased erosion and sediment buildup.
A team led by Muhammad Naveed Zafar at the University Savoie Mont Blanc combined historical records, geological data, and computer simulations to understand the events.
They found that farming since Roman times had tripled the amount of sediment reaching the lake, overloading the delta and making it prone to collapse during earthquakes. The team determined the 1117 collapse moved approximately 62 million cubic meters of sediment, creating waves that reached the shoreline within a minute and flooded areas up to 2.7 kilometers inland. The smaller collapse in 1222 generated waves around 13 meters high.
Historical records, including a 12th-century manuscript in the Vatican Library, corroborate the events, noting significant damage to nearby villages. Today, the shores of Lake Iseo are densely populated, and the delta has rebuilt after a period of reduced erosion following the Black Death. The researchers warn that another collapse could happen with little warning, and similar risks exist at other lakes, including Lake Garda and Lake Como, where sediment buildup has occurred.
They emphasize the importance of considering both geological faults and historical land use to assess the danger of lake tsunamis.
