Ginkgos and Rhythmites

Our vacation in the flood-ravaged landscapes of the Pacific Northwest came to an end where Interstate Highway 90 crosses Lake Wanapum on the Columbia River.  We had covered only about a third of the distance that the great Ice Age floods had traveled.  But we had no choice, we were out of time.

Route of the Ice Age Floods; red arrow marks the end of our vacation.  Map from the Ice Age Floods Institute; click on photo for closer view.

On the way home we managed to squeeze in two more quick geo-stops.  In hindsight, I see they nicely bracketed the range of time and events underlying the landscapes we had enjoyed so much.

Miocene Trees

From displays at Dry Falls Visitor Center.

It’s fascinating to imagine what a place was like far in the past, when our continent was somewhere else on Earth and the topography was not what it is today (e.g. no Cascade Range).  Of course the climate was very different, as was the vegetation.  Twenty thousand years ago there were lush forests in eastern Washington instead of today’s steppe/grasslands and wheat fields.

Then three million years later came the period of massive volcanism that would cover 64,000 square miles of the Pacific Northwest in lava flows (Columbia River Basalt Group).  It’s thought that some of these flows dammed lakes where dead trees accumulated, or perhaps lahars (mudflows) associated with volcanic eruptions deposited huge piles of dead trees.  In any case, the accumulations were then buried in basalt.  Instead of rotting, the wood was replaced with silica.  Millions of years later erosion exposed the petrified wood for travelers like us to enjoy, as we did during a short visit to Ginkgo Petrified Forest State Park near Vantage, Washington.

Some of the petrified logs look quite real, like this one with its "peeling bark" ...

Here's a nicely-preserved knothole:

We made only a brief stop and didn't take advantage of the trail through petrified logs of many species.  Forty kinds of trees grew in the Miocene Forests here, not just ginkgos.

Ginkgo Petrified Forest State Park --  46.969417° -119.982646°

Interlude

Most of the basalt was produced 17 to 15 million years ago, but activity continued until about six million years ago.  Fast-forward five million years and one would find much of eastern Washington covered in dunes of loess -- fine windblown sediments.  Today the fertile loess-derived soils are highly-productive, and are covered in wheat and irrigated crops.  But among the wheat fields are weird intriguing dark rocky sparsely-vegetated landscapes called scablands.  Something happened here ...

Huge fallen chunks of basalt, ripped out and carried by floods.

Late Pleistocene Lakebeds

If you’ve been following this series of posts, you know that near the end of the last glacial advance there were floods of tremendous proportions that raced from an immense lake in northwest Montana all the way to the Pacific coast, arriving in perhaps just a few days.  That much water traveling at those speeds was hugely destructive.  The floods scraped off the blanket of loess over large areas and carved the underlying basalt as well, forming the scablands of eastern Washington.  That's where we spent most of our vacation.

Above, Dry Falls 15,000 years ago (Montana Natural History Center); below, Dry Falls on a hot September day in 2013.

Our final Pleistocene flood stop was a short distance south of Spokane at Campion Park on Latah Creek.  It didn’t really look like a park -- we saw no sign nor facilities.  But thanks to Bruce Bjornstad’s handy guidebook (see Resources below), we found it easily in spite of the road construction.  We pulled off, parked among the weeds and walked along the creek a short distance.

Photo by DM.

Across the creek from the park are Pleistocene rhythmites exposed in eroding slopes below nice houses.  Rhythmites are repeated deposits, in this case due to repeated flooding.  The current interpretation is that water from Glacial Lake Missoula flowed into another huge ice age lake -- Glacial Lake Columbia (see map near top of post).  The Latah Creek drainage was once an arm of the flooded lake. When the waters dropped and calmed after the flood went by, sediments settled out -- coarse first, then finer.  Likewise, the rhythmite bands are graded from coarse to fine from bottom to top.  Within the top part of some bands are much thinner layers interpreted as varves, annually-deposited rhythmites.   These at Latah Creek may represent summer runoff from melting glaciers.  JG Rigby recognized 20 separate flood events on Latah Creek (se Allen et al. 2009, Bjornstad 2006 below).

Note holes in rhythmites.  Something finds the old lake bed sediments useful ... ??

Campion Park,  47.607821° -117.379168°

What’s Next?

Of course this isn’t the end of the scablands story -- it’s just all that’s been written so far.  What will happen next?

Some say we’re currently in an interglacial period.  The climate will eventually cool and ice sheets will advance south again.  If so, sea level would drop, providing abundant seaside real estate.  But lobes of the great ice sheets may again impound immense lakes, and the dams may periodically fail.  It might be best to move south instead.  How about the scablands?  Will they expand, and be sculpted into even more fantastic forms?  Will Dry Falls flow again and continue to move upstream as kolks tear at the basalt?

The Dry Falls Visitor Center may have to be moved upstream if there are more Ice Age Floods.

Unfortunately, looking far into the future is a less-than-satisfying exercise.  My brief life on Earth, though informed by geology, keeps me from realistically imagining such worlds.  The scenes I try to envision are hardly vidid, just flat dull inanimate landscapes.

The near future is much easier to conjure up.  I foresee another trip ... we’ll cross the southern scablands, pass through the Columbia River Gorge, gawk at the Willamette Valley, and then happily find ourselves among the Miocene basalt headlands of the Oregon coast.

Source.

Resources for Travelers

Geo-tripping in Pleistocene flood country is wonderful in part because there are so many good resources to help travelers understand the landscapes.  In fact, there now is an Ice Age Floods National Geologic Trail.  It’s not a single route, but rather a collection of tours and stops from northwest Montana to the Pacific coast.  The IAFNGT is still under development.

Some useful websites (I'm sure there are many more)

Ice Age Floods Institute

HUGEfloods.com

Glacial Lake Missoula and the Ice Age Floods

Glacial Lake Missoula and the Missoula Floods

Washington State Parks -- Ice Age floods sites (map below)

Books and articles:

Allen, JE, Burns, M, and Burns, S.  2009.  Cataclysms on the Columbia.  Portland State University, Ooligan Press.  [I especially enjoyed MB’s contributions -- how geologists do their investigations, the saga of J Harlan Bretz and his radical flood scenario, and descriptions of what it might have been like to witness the events.]

Ault, D.  2001.  Glacial Lake Missoula and its Humongous Floods.  Missoula, MT:  Mountain Press Publ. Co.  [This book planted the seed that grew into a geo-trip through the scablands.  What a story -- and true!]

Baker, VR.  2009.  The channeled scabland:  a retrospective.  Ann Rev Earth Planet Sci 37:393-411.  PDF available.

Bjornstad, B.  2006.  On the trail of the ice age floods.  Sandpoint, ID:  Keokee Books.  [The second of two guides, this one on the northern part of the scablands.  Bjornstad provides detailed descriptions of trails, drives, and things to see along the way ... a great resource.]

Soennichsen, J.  2012.  Washington’s Channeled Scablands Guide.  Seattle:  Mountaineers Books.  [This proved to be a useful guide for first-time visitors, with recommended hikes, drives and camping].

On the ground

Early on we stopped at the Montana Natural History Center in Missoula and found maps and illustrations that gave us a good overall picture of where we were going and what had happened there.

Missoula, Montana 15,000 years ago.

At the Dry Falls Visitor Center, we took in the interpretive displays and bookstore, and enjoyed great scabland views.

Perch Lake in the coulee below Dry Falls.

The Montana Department of Transportation has put together a network of informative roadside geo-stops, and a website to go with it.  That’s a very cool Department of Transportation!

Vacationing geo-geek in Clark Fork Canyon, Montana.  Photo by DM.

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

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.

Sources

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.

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?

Source.

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.

Sources

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.

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.