Sunday, September 29, 2013

Lakes and Floods of Unimaginable Proportions

Traveling north on Montana Highway 200 -- 15,000 years ago.
Continuing along the trail of Ice Age Mega-floods, we arrived at Sand Point, Idaho, site of the ice dam that impounded Glacial Lake Missoula.  It was time to stop and ponder the immensity of the lake and the unimaginably huge and swift floods that cut loose whenever the ice dam failed.
Glacial Lake Missoula was dammed by ice 15,000 years ago (MT Dept. Transportion).

How big was the lake?

JT Pardee of the US Geological Survey was mapping the geology of northwest Montana when he came across old lake shorelines high on valley slopes (Pardee 1910).  He concluded there had been an immense lake during the last glacial advance, and called it Glacial Lake Missoula.  The highest of the shorelines stands 4250 feet above sea level, 900 feet above Missoula and 2000 feet above Sand Point.  Based on the high-water mark, the lake covered some 2900 square miles and contained 530 cubic miles of water.
   Relief map hand-painted along high-water contour line to recreate Glacial Lake Missoula.
Click on photo to view detail.  From Montana Natural History Center in Missoula.

How big was the dam?

The ice that impounded Lake Missoula was a lobe of the Cordilleran ice sheet that extended south via the Purcell Trench and blocked the Clark Fork River near Sand Point.  Estimates put the size of the dam at 2000 to 2500 feet in height and more than 30 miles across.
Mouth of Clark Fork River at Lake Pend Oreille; arrow marks approximate location of ice dam.

How big were the floods?

It’s not easy to measure floods that took place 15,000 years ago, but we do know a few things.  They reached the Pacific Ocean after traveling on the order of 500 miles from Sand Point.  They didn’t take a direct route, but rather spread out in huge braided networks.  Sometimes the floods encountered tight spots, temporarily impounding large lakes.  Allen et al. estimate that more than 16,000 square miles were flooded and scoured out.
Scablands of eastern Washington.  Tan wheat fields and grassland; green irrigated fields (lower left); brown areas of basalt bedrock exposed by floods.  From Google Earth; click on photo to view.
Flood depth varied with topography, but was on the order of hundreds of feet.  For example, it’s thought that 700 feet of water flowed over today’s Dry Falls at peak flood, with the “falls” visible only as a bump in the raging torrents.
Dry Falls back in the day, from the Montana Natural History Center.  At peak flow, the surface of the water is thought to have been even higher -- well above the tops of the cliffs.
Dry Falls in the early 21st century.  On this hot September day it was very difficult to imagine what it was like during Pleistocene times!

How fast were the floods?

Glacial Lake Missoula probably “emptied” in two or three days, not counting lakes and ponds left behind after the level dropped below drainage divides.  It took only a few days for these huge masses of water to reach the Pacific Ocean.  Speed estimates range from 30 to 80 miles per hour, depending in part on width of the flood path.  Considering the volume of water and debris, this is scary!  It’s thought that water, ice, dirt and rock “surged” out of Lake Missoula at around 9.5 cubic miles per hour (Allen et al.).

One way to calculate speed is to look at the size and form of features created by the floodwaters, like the giant current ripples of Camas Prairie.  These are up to 45 feet in height and several hundred feet apart, and many are antidunes -- evidence of very rapid flow.  The raging waters scraped off 150-200 feet of soil and dirt, and plucked boulders weighing tons out of the underlying bedrock.  Allen et al. estimate that almost 50 cubic miles of soil, sediment and rock were removed.
Giant current ripples form alternating dark-light pattern in mid-ground.

How many floods were there?

J Harlan Bretz, who argued that the bizarre landscapes of eastern Washington were created by catastrophic flooding long before anyone else accepted the idea, proposed a single mega-flood which he called the Spokane Flood (he didn’t know of Glacial Lake Missoula at the time).  Current thinking is that there were multiple floods, perhaps as many as a hundred, over a period of about 3000 years.  Not all were mega-floods, and there may have been other sources.  But the flood of 15,000 years ago probably was the largest, and the main water source was Glacial Lake Missoula.

What do all these numbers really mean?

While it’s easy to write that 530 cubic miles of water and debris flowed from Glacial Lake Missoula to the Pacific Ocean at speeds sometimes approaching 80 mph, it’s pretty hard to wrap my brain around these dimensions, though they certainly sound catastrophic.  Perhaps we can better comprehend the enormity of the mega-floods by comparing them with things we know.

Glacial Lake Missoula often is compared to existing lakes.  At its largest, it contained half the volume of Lake Michigan, and as much as Lakes Erie and Ontario combined.  The ice dam across the Clark Fork River was so tall that “with room to spare, two Empire State Buildings could have stood one atop the other against Glacial Lake Missoula's ice dam” (PBS NOVA).  The biggest of the floods contained ten times the flow of all rivers of the world and 60 times that of the Amazon -- and it reached the coast in just a few days!

Allen et al. (Appendix C) compare Lake Missoula floods with 22 examples of more familiar catastrophes in terms of energy expended.  The largest Missoula flood probably was similar in magnitude to the meteorite impact credited with the Great Extinction 66 million years ago.  It is estimated to have had almost 400 times the energy of the 1906 San Francisco earthquake, 75 times that of the largest fusion (nuclear) bomb, more than ten times the energy expended during the first eight hours of the 1980 Mt. St. Helens eruption, and 26% of all energy produced in the USA in 1970.

What would it have been like to experience a mega-flood?
By Stev Ominski, from the Ice Age Floods Institute.
There’s another question that comes up repeatedly -- did humans witness the catastrophic floods?  Whether people lived in the Pacific Northwest at that time is still debated.  If there were witnesses, they left no record.  Fortunately, being human, we can imagine what it might have been like to hear a distant escalating roar, and then to see an immense mass of swirling water, ice, rocks and dirt approaching at frightening speeds.
“... depending on how far away you were, there would have been a lot of stress and a lot of noise from boulders banging together. You might also have seen rather bizarre things—huge waves, for instance, perhaps even particles flying out of the flow. That would have been rather disconcerting.”  Vic Baker interviewed on PBS NOVA
“Imagine the kind of velocity the water had when the flood came through, the tremendous air blast caused by the wave front.  Its roar would have built for a half-hour at least ...” Leonard Palmer, Northwest Magazine, June 26, 1983 (in Allen et al.)
“In a scene belonging more to the realm of science fiction than to reality, this towering mass of water and ice ... literally shook the ground as it thundered toward the ocean”  From poster at information center in northwest Montana
“how can we imagine a torrent of air exploding into existence, driven by a wall of water hundreds of feet high and moving at 60 miles per hour ... [and] this wall may well have come at night.”  Marjorie Burns (in Allen et al.)
And what would it have been like to watch Lake Missoula drain ... to watch a huge body of water, which surely had always been there, simply disappear?
“The lake, he realized, was moving, and currents of muddy water were starting to tear at the banks. He watched, stunned, as the lake level started to drop. From his vantage point on the high ridge, he could see water surging through the gap in the hills, tearing away at the soil and rock. He could hear giant boulders bouncing in the depths.”  Geotripper; for more, read In the Land of the Great Draining.
Another way to experience a Pleistocene mega-flood is through digital simulation.  Here you can watch 530 cubic miles of water race from Sand Point to the Pacific Ocean.

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


Allen, JE, Burns, M, and Burns, S.  2009.  Cataclysms on the Columbia.  Portland State University, Ooligan Press.  NOTE:  This is recommended reading: information-packed, interesting, enjoyable.

Pardee, JT.  1910.  The Glacial Lake Missoula, Montana.  J. Geol. 18:376-386.

Wednesday, September 25, 2013

Paperblog & Tafoni Report

Tafoni -- curious pockets in rock.
Emma contacted me last week with an invitation to join Paperblog:
“Having come across your blog, In the Company of Plants and Rocks, I wanted to get in touch to introduce you to Paperblog. We are a new media sharing platform for blog writers and we would like you to be a part of it.”
So far I’ve learned that this is a blog aggregator, with some 20,000 blogs organized into “magazines”.  Plants and Rocks would be included in the Outdoor one.  It appears that Paperblog makes money through advertising, and participants get the hope of increased readership.  Anyone can submit a blog for consideration.

Do you paperblog?  If so, any information or advice would be appreciated!
What does Paperblog have to do with tafoni?  Nothing really.  Participation requires this validation article, and for interest I'm including photos from a recent trip to the eastern edge of the Colorado Plateau, near Grand Junction, Colorado.
“I confirm the subscription of this blog to the Paperblog service under the username hollis”
Whenever I hike in McInnis Canyons I become enchanted by the many holes and pockets in the rock, called tafoni.  They're whimsical in shape and arrangement, and maybe-just-maybe one will lead to a secret path!
How do tafoni come to be?  There are many hypotheses.  In fact, there’s an entire website devoted to what we know, think and speculate about tafoni.
In the Entrada sandstone in McInnis Canyons, tafoni often occur in lines along bedding planes (above and below; click on photos for better views).  Perhaps some sediment layers included small rocks as well as sand.  When exposed by erosion perhaps the rocks fell out, leaving little holes that expanded with time.  Perhaps.
We found other kinds of tafoni.  In one area, many little pockets covered brown sandstone boulders, possibly part of the Summerville or Morrison Formations -- a diverse collection of strata above the Entrada.
Sometimes one surface would be covered with small tafoni while orthogonal to the pock-marked side was cross-bedding.  Hmmm ... how did this come to be?
Tafoni often set my mind to wandering.
Some tafoni showed signs of habitation, by various critters:
Bird's nest.
Black dog seeking shade.
Happy geo-geek.
More tafoni can be found in reports from 2012:  McInnis Canyons, Rabbit Valley, the Honeycombs, and the Central California Coast.

Sunday, September 22, 2013

Cedars of the Thuja kind

"the branches appear flattened as if they had been ironed" (Rocky Mt Tree Finder)
During our recent tour of Pleistocene flood landscapes we were driving through the Clark Fork River canyon which 15,000 years ago contained on the order of a thousand feet of water before it drained in a flood of of immense proportions, when we were side-tracked by something very different -- trees.  In small print on the Montana highway map was the promise of “giant cedars”.  We couldn't resist and headed off to the Ross Creek Giant Cedar Grove, where we took a wonderful one-mile walk through shade and light.
These are western red cedars, Thuja plicata.  Scientific (Latin) names may seem pretentious but in this case they clearly are useful, for there are many kinds of “cedars” in the world.  They aren’t just different species either, but completely different genera (plural for genus).  In other words they aren’t even closely related.  Here are some examples:
True cedars belong to the genus Cedrus.  They’re native to the western Himalayas and the Mediterranean region.  Examples include Deodar cedar and the Cedars of Lebanon.
The red cedar we talk about in South Dakota actually is a juniper, Juniperus virginiana.  The wood made great fenceposts before steel ones arrived.
The white cedar of Australia, Melia azedarach, isn’t even a conifer.  It’s a member of the mahogany family.
Range of western red cedar, Thuja plicata.  Source.
Western red cedar is native to the Pacific Northwest, reaching its easternmost limit in northwest Montana.  It has always been important to humans because it’s so resistant to decay.  It was and still is used by indigenous peoples and is of major economic importance for the rest of us, but that’s beside the point.  These are impressive and charismatic trees in and of themselves, as we discovered.
Western red cedars are big.  The largest are second only to giant sequoias in volume.  The mature cedars of the Ross grove are "only" about 400 years old (vs. 800-1000 years for the most ancient) so they aren't all that large, but they sure seemed big to us.  Our Wyoming trees are pretty puny in comparison.
It took us forever to tour the Enchanted Red Cedar Forest as there was much to see and ponder.
Bases of mature trees often are gracefully buttressed.
Branch ends are distinctly flattened and fern-like, making western red cedars easy to recognize.
Closeup showing scale-like leaves.
A Tree-Hugger.
Ross Grove is accessible via a four-mile winding road.  It's well worth a visit.

For more about western red cedars, see the USDA Fire Effects Information System.

Thursday, September 19, 2013

Of Mosses and Mountains II and AW #60

The Apennines -- home to momentous discoveries in geology.
As mentioned earlier, my summer reading included two outstanding books about natural history.  The first, Gathering Moss by Robin Kimmerer (reviewed here), is about the miniature fairy-tale world of mosses.  The second concerns the other extreme -- a world at an almost-incomprehensible scale where landscapes are as ephemeral as patches of moss.  This is The Mountains of Saint Francis, by Walter Alvarez (W.W. Norton, 2008; also recommended by Rapid Uplift and Geology).

As hinted at in the subtitle -- Discovering the geologic events that shaped our earth -- Alvarez uses the Apennines of Italy as a venue for describing great discoveries in geology.  He tells of the brilliance of the discoverers, the far-reaching effects of their discoveries, and the generally reluctant acceptance by colleagues.

How nice that the topic for this month’s Accretionary Wedge happens to be Momentous Discoveries in Geology!  Thanks to Matt at Geosphere for his timely choice :-)
“The discovery you choose does not have to be universally recognized as momentous but should be in your opinion. It could be something that we take for granted every day, but is in actuality part of the underpinnings of our science.”
After reading The Mountains of Saint Francis, my choice is the very basic realization that the Earth changes at a scale well beyond that of our lifetimes.  We might see a volcano pour out massive amounts of ash, or suffer through a destructive earthquake, but these are just minor events.  Consider that mountain ranges are uplifted and then worn away, and that continents move around, collide, split and even sink, coming apart in the process. Humans can only experience these kinds of changes with their imaginations, and even that wasn't always possible.

Who was it that “discovered” that the Earth has a history well beyond what is witnessed by humans?  Alvarez credits Nicolas Steno (1638-1686), often considered the founder of geology.  So the Earth changes ... I certainly take this for granted, it seems so obvious! But in Steno’s day it wasn’t easy to convince people that seemingly abiding landscapes are ephemeral.
Fossils were the key to Steno’s “discovery”, allowing him to argue convincingly that the hills around Tuscany once were sediments on the ocean floor, even though no human had seen nor recorded such a spectacular change.  At the time, fossils were considered growths within rocks in spite of obvious similarities to living organisms.  Steno was not the first to propose that fossils were once alive, but his careful studies and convincing arguments led to general acceptance.  He saw the problem as one of explaining “a solid body naturally contained within a solid” (De solido intra solidum naturaliter contento), and noted that:
If a fossil had grown within a rock it would distort or crack the rock, which was never the case.
Many fossils appeared to be falling apart rather than growing; in fact discrete fossils sometimes fit together perfectly.
Fossils were never distorted in shape, contrary to what would happen if growing in hard rock (like tree roots).
Fossil shells were sometimes found in clusters, arranged just as they are in the ocean.
Steno reasoned that rocks containing fossils and other solids had once been fluid, and had hardened around those solid objects.  Thus seashells fossilized in the mountains had once lived in the ocean, i.e. the mountains had not always been there.  The Earth has undergone huge changes; it has a history, which geologists have been working to unravel ever since.
"One sins against the majesty of God by being unwilling to look into nature's own works and contenting oneself with reading others" said Bishop Steno.
Steno’s mind in action must have been awesome to behold.  From his study of fossils, he went on to explain layered rocks (principle of original horizontality) and how they can provide powerful insight into the history of the Earth (law of superposition).  No wonder Steno is considered the Father of Stratigraphy.

Obviously Steno was an open-minded and visionary thinker.  And I suspect he wasn't afraid of the unknown ... that he did not feel obligated to fit everything into existing stories, which of course would have limited his amazing thinking.
“Fair is what we see, Fairer what we have perceived, Fairest what is still in veil.”
Modified from source.

Tuesday, September 17, 2013

The “Unusual Currents” of JT Pardee

Looking east-southeast from interpretive sign on Road 382.
This is Camas Prairie in northwest Montana, home to some very curious ridges and swales (mid-ground in photo).  The crests are as much as 45 feet high, but this is hard to see at ground level even though the vegetation -- pale on ridges and dark in swales -- helps highlight the shapes.  In contrast, these landforms are quite obvious from the air.
Ripples on the prairie.  From Google Earth; click photo for better view.
From the air, the ridges and swales look a bit like ripples that develop in beach sand washed by waves or on sandbars in rivers.  Might this be a clue?
Possibly, except there’s a problem.  The Camas Prairie ridges aren’t made of sand.  They contain gravel, cobbles and even boulders, which are much too large to be arranged into current ripples ... or are they?
More curious ripples on the prairie, looking southwest.
It was Joseph Thomas Pardee who made the great conceptual leap ... and without the aid of aerial photos!  He concluded that these ridges are indeed ripples, produced by "unusual currents" in massive floods when huge volumes of water traveled at cataclysmic speeds (Pardee 1942).  The source was Glacial Lake Missoula, which we had visited the day before.
Old shorelines of Glacial Lake Missoula visible on right side of “L” hill.  Click photo to view.
Lake Missoula formed when a lobe of the Cordilleran ice sheet dammed the Clark Fork River near Sand Point, Idaho, forming a huge lake (map below).  When the dam gave way around 15,000 years ago (largest of multiple flood events) the lake drained at tremendous speeds, enough to create giant current ripples composed of very coarse materials.  The height and spacing of the ripples have been used to estimate rate of flow, perhaps as much as 60 to 80 miles per hour.

The shapes of the ridges also attest to the speed of the flood.  Many are antidunes, with steeper sides facing upstream, indicating that water movement was quite rapid.  The Camas Prairie basin drained north across Markle Pass, and eventually into the main channel of the Clark Fork River.
Before the big flood, Camas Prairie sat under 1000 ft of very cold water.  Map of Glacial Lake Missoula from Montana Natural History Center
Another great geo-stop, courtesy Montana Department of Transportation.

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


Allen, JE, Burns, M, and Burns, S.  2009.  Cataclysms on the Columbia.  Portland State University, Ooligan Press.

Pardee, JT.  1942.  Unusual currents in Lake Missoula, Montana.  Geological Society of America Bulletin 53:1569-1599.

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.