Thousands of years ago, the eastern flank of the mountain experienced a catastrophic collapse, generating an enormous landslide in an event similar to that seen in the 1980 eruption of Mount St. Helens. The landslide left a large depression in the side of the volcano, known as 'Valle del Bove' (Valley of the Ox). Research published in 2006 suggested this occurred around 8000 years ago, and caused a huge tsunami, which left its mark in several places in the eastern Mediterranean. It may have been the reason the settlement of Atlit Yam (Israel), now below sea level, was suddenly abandoned around that time.
The steep walls of the valley have suffered subsequent collapses on numerous occasions. The strata exposed in the valley walls provide an important and easily accessible record of Etna's eruptive history.
The most recent collapse event at the summit of Etna is thought to have occurred about 2,000 years ago, forming what is known as the Piano Caldera. This caldera has been almost entirely filled by subsequent lava eruptions, but is still visible as a distinct break in the slope of the mountain near the base of the present-day summit cone.