Friday, September 6, 2013

FFF: Glacial Lake Missoula

One of Montana Department of Transportation's great roadside signs.
FFF stands for “Five Fact Friday”, a creation of Tim Havenith at Notes of Nature.  Today being Friday, I’m borrowing it for a post about Glacial Lake Missoula (thanks, Tim).  We’ve been driving along the old lake bed for two days now.
This was under  many hundreds of feet of water not all that long ago.
Fact 1.  During the last glacial advance, a lobe of the continental ice sheet formed an ice dam in the vicinity of Sand Point, Idaho, blocking the Clark Fork River drainage and creating a huge lake -- Glacial Lake Missoula.
Diagram showing ice dam, by MT DOT, Alberton Parking area on I-90 between MP 72 and 73.
Extent of Glacial Lake Missoula (dark purple), with ice sheet to north (white) and floods to southwest (bluish); from the Montana Natural History Center.  Date is uncalibrated radiocarbon years.
Fact 2.  Missoula, Montana, sits 900 feet below the highest relic shorelines.
Artist’s rendition of the Missoula area 15,000 years ago, from the Montana Natural History Center.
Relic shorelines on “L” Hill, most notable on slope and edge to right (click photo to view).
Fact 3.  Sometime around 15,000 years ago the ice dam floated and failed, letting loose a jökulhlaup.

Fact 4.  A mass of water, ice and earth hundreds of feet deep poured downstream at 60 to 80 mph, altering the landscape all the way to the Pacific Ocean.

Fact 5.  The Scablands of eastern Washington were the result of this flood and others like it (maybe as many a hundred during the last glacial advance).  That’s where we’re headed.
Heading north on Interstate 90 along the bed of Glacial Lake Missoula -- looks like the area could use another episode of scouring and cleaning!

This post is part of a series about the Ice Age Mega-floods of the Pacific Northwest.


  1. Cool post. I really like you use of the maps. Also, thanks for linking to my blog; it's very kind of you.

  2. Very Interesting. I did not learn of Lake Missoula until my son and his future wife moved to Missoula.

    Last winter I read an incredible book, Mapping Mars. I have been looking for it to quote from it, but it remains unfound. At any rate, the author describes some chaotic landscapes on Mars that appeared to be caused by a catastrophic flood. One of the Mars Geologist spent several weeks driving Lake Missoula and then comparing his finding with what he was seeing on Mars. It is now accepted that the jökulhlaup area he saw on Mars resulted from a flood similar to when Lake Missoula breached.

    I recommend the book. It gets five stars out of five. The reference is: Mapping Mars: Science, Imagination, and the Birth of a World by Oliver Morton

    Don Bailey

    1. Thanks, Don. This is an area I heard about a long time ago, now finally I have arrived. The book sounds great ... I will try inter library loan after I get back.

      Cheers, Hollis