# Lake Iseo delta collapses in 1117 and 1222 triggered tsunamis with run-ups of ~50 m and ~13 m

- Published: 2026-11-11 00:30 UTC
- Section: Planet › Earth sciences
- Tags: Lake Iseo tsunami, lacustrine tsunami, subaqueous delta collapse, 1117 earthquake, 1222 earthquake, human-induced erosion, Oglio delta, Nature Communications, lake hazard assessment
- URL: https://realtech.media/news/rt-77686d5a345a84e4765e38db_lake_iseo_delta/

**Geological records and simulations show that two earthquakes triggered subaqueous delta collapses in an Italian lake; the authors link the delta's instability to human-driven erosion.**

![Lake Iseo delta collapses in 1117 and 1222 triggered tsunamis with run-ups of ~50 m and ~13 m](https://realtech.media/media/2026/11/d65304501da4d69e.webp)
*science-et-vie.com*

A team led by Muhammad Naveed Zafar of Université Savoie Mont Blanc reported in Nature Communications that earthquakes in 1117 CE (Mw 6.5) and 1222 CE (Mw 6.0) triggered major subaqueous collapses of the delta in Lake Iseo, northern Italy. According to geological records and numerical simulations, the resulting tsunamis had maximum run-ups of about 50 m and about 13 m, respectively [1].

The reconstruction is supported by historical accounts from the Vatican Library and by archaeological evidence [1]. A twelfth-century manuscript kept there says the lake rose so high that almost no one survived. The authors report that the model is consistent with this account.

## Sediment load and delta stability

The authors show that two millennia of intensified land use tripled the sediment flux into the lake, oversteepening the delta and preconditioning it for failure [1]. The delta is fed by the Oglio river. According to the report, forests of the Val Camonica retreated in favour of pastures and mines, which weakened the hold of the soil on the slopes.

## Simulated waves and the risk today

For the 1117 event, the simulations place the volume of sediment that slid underwater at about 62 million cubic metres. Near the northern shore the wave exceeds 50 m, reaches up to two kilometres inland and arrives at the villages in less than a minute. At the town of Iseo the water rises by about 5.5 m, six to seven minutes after the slide. The 1222 collapse was smaller; the island of Monte Isola split the wave and partly shielded neighbouring settlements.

Since the last collapse, eight centuries of human-induced erosion have rebuilt the delta. The authors conclude that shoreline populations remain highly vulnerable to future earthquake-triggered failures [1].

The study also includes a global lake synthesis. It shows that human-driven erosion has reached its highest levels since the Industrial Era and is progressively overloading deltas worldwide. On this basis the authors state that similar catastrophic failures may become more likely, and that the mechanism matters for hazard assessment [1]. The sediments of lakes Como and Garda also preserve traces of medieval collapses.

## Sources

1. [Nature Communications](https://doi.org/10.1038/s41467-026-78272-8)
2. [science-et-vie.com](https://www.science-et-vie.com/nature-et-environnement/en-1117-les-habitants-du-moyen-age-auraient-contribue-a-declencher-deux-tsunamis-dans-un-lac-les-vagues-auraient-depasse-50-metres-265804.html)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-77686d5a345a84e4765e38db_lake_iseo_delta/