Segments in this Video

Introduction: Killer Floods (02:01)


Earth is geologically active; extreme events have occurred in the past and could happen again. Scientists discover evidence of floods powerful enough to blast through rock in landscapes around the world.

Record Events (02:40)

Water surges kill 25,000 people annually; in 2004, a tsunami hit Southeast Asia; in 2017, Hurricane Harvey devastated Houston and monsoons ravaged Bangladesh. Evidence of floods capable of carving new landscapes is discovered in Washington State, Iceland and Britain, and discussed by scientists.

Scablands Mystery (05:48)

The plains covering 1600 square feet of Washington State change abruptly; flat fields give way to rock islands, gorges and massive depressions. A geologist tours the area in hopes of discovering signs of formation; Dry Falls, a 400 foot high horseshoe shaped canyon, and super-sized sink holes are indicators of colossal floods.

Asbyrgi Canyons (04:31)

In Iceland, there is topography reminiscent of the Scablands; a geomorphologist suspects similar formation processes. He uses surface exposure dating to detect elemental changes in Asbyrgi Canyon rocks; they were created by one epic natural event.

Force of Water (02:26)

Smaller floods can be dangerous and cause damage to civilization. In 2002, Canyon Lake Reservoir overflowed, leaving a 23 foot deep, mile long gorge, and providing proof that floods can transform landscapes in days.

Vatnajokull Ice Cap (02:42)

In Iceland, seven volcanos lay underneath Europe's largest glacier; in 1996, Grimsvotn erupted, melting enormous amounts of ice in hours and causing structural damage. A geophysicist monitors activity and discusses the lake he discovered below; he believes flood waters from the ice cap formed the Asbyrgi Canyons.

Glacial Lake Missoula (08:13)

A geologist uses surface exposure dating at the Scablands; they were formed 16,000 years ago. In Montana, a geologist explains the horizontal lines on hills and glacial scratches on cliffs, indicating Missoula valley was once a massive lake dammed by ice. The body was large enough to carve the Washington landscape, and leave behind giant rippling hills.

Dam Failure (07:50)

In 1976, the Teton dam failed, having eroded from below; a geologist explains how the Lake Missoula glacier dam similarly degraded until suddenly collapsing. A researcher engineers a computer model confirming the flow's southwest path, and formation of the Scablands. Pacific Ocean core samples reveal repeated flooding as the ice dam broke and reformed.

Matching Geologies (04:40)

The English Channel separates England from France, and is flanked by almost identical, chalk cliffs. The white landforms are the calcium composite of micro organisms' skeletons. Flint is embedded in parallel bands on the cliffs, confirming that a ridge once connected Britain to Europe.

Forming the British Island (08:48)

A geologist explores the topography of the English Channel; she uses sonar to discover and map steep canyons, rock islands and channels reminiscent of the Scablands; she discusses the massive water movement required to form the terrain. 450,000 years ago, an ice age pervaded the area, and dammed the North Sea; melt water weakened and collapsed the chalk ridge, carving a channel to the Atlantic Ocean.

Future Events (03:01)

Evidence of landscape changing mega-floods is found in Vatnajokull, the English Channel, and the Scablands. In Iceland, active volcanos threaten ice integrity, but not humanity. Glacier mountains currently pose the greatest flood threats to civilization.

Credits: Killer Floods (00:38)

Credits: Killer Floods

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Killer Floods

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In Killer Floods NOVA discovers gigantic scars in the landscape that testify to North America’s greatest ever megaflood, which tore across the western states with 60 times the flow of today’s Amazon.

Length: 54 minutes

Item#: BVL166848

Copyright date: ©2017

Closed Captioned

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