Land use helped load Lake Iseo’s underwater slopes before medieval tsunamis
A single peer-reviewed study links land use around Italy’s Lake Iseo to sediment buildup that made underwater slopes more vulnerable to collapse. Geological evidence and simulations reconstruct two medieval tsunamis following earthquakes. The results describe how erosion can alter a lake’s physical hazards, with wave impacts varying sharply along its shores. They do not forecast a future earthquake.
Science··Evening
Erosion built an unstable underwater delta
Land use around Lake Iseo in northern Italy increased the sediment entering the lake and steepened the underwater slopes of its delta. A single peer-reviewed study combines geophysical measurements, sediment evidence, historical accounts and simulations to reconstruct the resulting hazard. Sediment inputs rose roughly threefold over two thousand years of expanding human use of the surrounding land. Accumulated material helped prepare the slopes for large collapses when earthquakes shook the region.[1]
Medieval collapses sent waves across the lake
The reconstruction links major delta failures to earthquakes in 1117 and 1222. Simulated maximum local run-up reached about 50 m and 13 m respectively. Run-up measures the height water climbs on land, and these terrain-dependent maxima do not describe a uniform wave around the shoreline. Monte Isola, the island in the lake, divided the waves and partly sheltered some settlements. Modeled impacts differed substantially between shore locations.[1]
Historical damage accompanies the geological evidence
A medieval account preserved in the Vatican Library describes flooding, while rebuilding at the church of Sant’Andrea fits the reconstructed period. The contribution of shaking and water to individual buildings remains uncertain. Sediment has rebuilt the delta during the centuries since the last collapse. The study investigates physical conditions relevant to lake-tsunami hazard; it does not predict the date or magnitude of the next earthquake.[1]
