is not known but may have been caused by an earthquake or simply the build-up of water pressure in the lake. As well as destroying the isthmus that connected Britain to continental Europe, the flood carved a large bedrock-floored valley down the length of the English Channel, leaving behind streamlined islands and longitudinal erosional grooves characteristic of catastrophic megaflood events. Swiss Alps The 1818 Giétro Glacier catastrophe, killing 44 people, originated in a 4-km long valley located in south-western Switzerland. Fatal flooding was known during historical times with 140 deaths first recorded in 1595. After an increase of the glacier during the "Year Without a Summer", an ice cone started to form from the accumulation of falling seracs. During 1816, the valley filled into a lake which emptied during the spring of 1817. In spring of 1818, the lake measured about 2 km in length. To stop the rapid rise of waters, the canton engineer Ignaz Venetz decided to drill a sluice hole through the ice, tunneling from both upstream and downstream sides of the ice dam at an elevation of about 20 metres above the lake surface. An avalanche interrupted work, so a secondary tunnel was then drilled for safety reasons as the waters rose to 10 metres below. Dangerous sloughing of ice delayed the work until finally a 198-metre-long hole was completed on 4 June, days before lake began to escape via the manmade waterfall on 13 June. Venetz warned the inhabitants of the valley of the danger as water was also escaping from the base of the cone. However, the cone began to crack on the morning of 16 June and at 16:30 the ice dam broke sending 18 million m3 of flood waters into the valley below. Americas Alaska During the late Quaternary, ancient Lake Atna in the Copper River Basin may have generated a number of glacial outburst floods. Some jökulhlaups release annually. Lake George near the Knik River had large annual outbreaks from 1918 to 1966. Since 1966 the Knik Glacier has retreated and an ice-dam is no longer created. Lake George might resume annual floods if the glacier thickens again and blocks the valley (Post and Mayo, 1971). Almost every year, GLOFs occur in two locations in southeastern Alaska, one of which is Abyss Lake. The releases associated with the Tulsequah Glacier near Juneau often inundate a nearby airstrip. About 40 cabins could