Glacial Lake Missoula Full

[Music] you imagine sitting on the shore of a massive lake covering the Missoula Valley and stretching 3000 square miles in every direction the water enough to fill two Great Lakes floods all but the tops of the tallest mountains in the western part of what is now Montana imagine a dam seven statues of Liberty tall made of crystalline blue ice the dam fails and the lake is gone in just a matter of days this is the story of glacial lake Missoula and the catastrophic events shaping our landscape thousands of years ago the echoes of those events can be heard today in the stories the rocks in the river tell those who are curious and who listened closely this scene 18,000 years ago began when glacial Lake Missoula was formed by a lobe of the court er an ice sheet 2,000 feet high and 30 miles long the glacier located at the Purcell trench a large Valley at Sand Point Idaho blocked the path of the Clark Fork River as the water rose to the depth of 2,000 feet behind the giant dam the lake embraced the flooded mountains with fewer like arms those arms included the Bitterroot Valley to the south the Flathead Valley to the north and an Eastern arm as far as Deer Lodge the massive ice structure strained under the pressure of the backed up water for a long time the lake bed composed of gravel and sediment compressed under pressure quiet water is lapped on the beaches of the extensive and intricate coastline and mountaintops peaked above the water's surface when we walk around Montana and we see the rocks around us geologist job is to be very observant and pay attention to those rocks and learn to tell the story of the history of the landscape and the history of Lake Missoula is a great example piecing together these different pieces of evidence these different rocks and landscape forms that individually didn't make a lot of sense until we put them all together and then we learned this really amazing story the ice fields built slowly over the course of two hundred thousand years the Purcell lobe formed the dam backing up the rivers water behind it as the climate warmed toward the end of the Ice Age the ice began to melt what had taken two hundred thousand years to build took a mere two thousand years to vanish the rising water and melting ice reached a critical breaking point dripping slippery ice chunks released their hold from the massive glacier where the dam met the mountain caft icebergs floated on the lake the front of the gigantic ice chunks bobbed in the water pushed by howling winds and waves the calving action triggered extensive sloughing known as rotational failure which chewed into the spine of the ice dam this action was so powerful that the enormous dam broke releasing a torrent of water glacial lake Missoula was gone so there's no question using this rotational mechanism that we could have gone started on the Montana side and eaten clear through the core of the dam and gone out the Idaho side once you get started down hill on the Idaho side the dam is it's gone because now you're working downhill on ever thinner weaker ice the calving of other glacial lobes in the lake launched thousands of icebergs in a navy that sailed the rushing river and piled up in narrow canyons the grinding ice left echoes on the landscape at Rainbow Lake Eddy narrows and other locations along the rivers course the rushing water tore through northern Idaho Eastern Washington the Columbia River Gorge Oregon's Willamette Valley and finally released its fury into the Pacific Ocean at Astoria imagine this cataclysmic event draining the entire ancient lake in not years not months but only a few days torrents of water destroying everything in its path the sound must have been deafening at once the waters receded and the dripping canyons were silent total devastation scoured land cleaned of all organic matter scarred with ripples frozen in time and drainages instantaneously reshaped amazingly this ice dam break happened not just one isolated time but at least two and maybe as many as one hundred times the Purcell trench refilling with ice backing up the river and then draining as if a giant had pulled a stopper out of a bathtub the impact of the discovery of glacial lake Missoula is repeated and rapid flooding has changed the way scientists like Jay Harlen Bretz up to current researchers today view epic events around the world these monumental events happened so long ago how can we know about these huge floods even though glacial lake Missoula is gone there are clues that the curious geological detectives have followed in the last 100 years to piece together the puzzle of this ancient lake bed and the events shaping our landscape follow the clues yourself and find more evidence of this amazing phenomenon in your own backyard as you explore post your photos on instagram with hashtag Montana Natural History Center let's get started it's afternoon on a clear March day in Missoula standing on the University of Montana campus you glance up at nearby Mount Sentinel and notice the uniform horizontal lines the lines are echoes of the ancient glacial lake Missoula Beach they are strand lines or shore lines they are our iconic feature I mean most people I guess you have to maybe be a curious sort but go what are these lines doing on the hill and might seek the story to understand it the term strandline it's kind of all-inclusive it is simply meaning where the water came in contact with the mountainside there exactly parallel along the mountain front they do not cross they are always the same and only a body of water could do that to a mountain and they look like beaches that's what they were they were multiple beaches up and down the mountain they were the highest on the mountain at the deepest part of the lake so in Missoula the lake was a thousand feet deep probably drained and filled 40 to a hundred times but it didn't always fill back to the same level as time went on the lake level dropped so that's why you see multiple lake levels at the time glacial lake Missoula was here it was quite desolate ice and ice water and icebergs and probably some hellacious storms you can stand in the middle of the oval at the University you can stand Chara's Park you can stand where we are now and and look at the lake lines on the hill I couldn't help but but see them every time I looked at jumbo and Sentinel and all the mountains around Missoula engraved stone markers placed by the glacial lake Missoula chapter of the Ice Age floods Institute show the high-water marks at 4200 feet on Mount Sentinel mount jumbo and Lake Como in the Bitterroot become a geological detective if you find a strand line take a selfie with it and post it on instagram with hashtag Montana Natural History Center traveling the backroads west of Missoula you encounter a spectacular landscape with dramatic mountain views framing open plains along Highway 200 from Dickson to Hera the site of undulating 30-foot giant ripples frozen in time at Camas Prairie Basin is eerie and striking how did they form and what story do they tell about the massive outburst floods of glacial lake Missoula the Camas Prairie ripples were a key piece of evidence advancing the theory of the rapid draining of the ancient lake Ripple's are a great thing and a great visual to think about so we've all been down to the river or down to the beach and seen ripples forming by the water and usually the ripples we see forming on the beach there in shallow water and these ripples are about an inch from one crest to the next I've actually got some ripples here recorded in Iraq and you can see the difference from one crest to the next is about an inch and this is a very natural process it's due to the transport of sediment by the water moving over it one of the real keys to breaking open the Lake Missoula story was when we realized that there were some ripples up in Camas Prairie just north of Missoula but these were ripples where the distance between one crest to the next is now about a hundred meters or about a football field and the height difference is about three meters or about ten feet and we realized that these were ripples they had to have been formed by water but the scale of that water movement was nothing like what we are used to seeing must have been a huge flood moving massive amounts of water and making ripples at a scale a hundred times larger than we're used to seeing the best place honestly to see the ripples is on Google Earth and to fly over Camas Prairie they're just gonna pop you're gonna see them they're gonna look just like ripples you've seen anywhere else until you realize that it's a valley that you're looking at and not a small pond you can drive there thinking this is the place that broke the lake Missoula story open head out to Camas Prairie to investigate the giant ripples that can be seen from space strained to hear the roar of the violent ancient waters heaving gravel into undulating waves on the lake bottom the ripples are now covered by quiet grasslands and vivid blue kamas flowers in ancient still life snap a photo and post it on the Montana Natural History Center website hashtag GLM giant ripples patterns of light and dark of horizontally layered soil decorate sections of i90 west of Missoula at 9 mile this geological artwork describes the rhythm of the ancient lake bed the comings and goings that compressed the dark mud and light-colored silt into the lines and pages of the glacial lake story have the rhythm i'ts revealed the entire story the answer is still being debated a riff might really means a sequence in the rocks that repeats itself over and over again what happens is in riff might is we have a period of time where the water is going very fast and it carries big material or bigger material and then we have a period where the water slows down and it drops smaller and smaller material and in a riff might this pattern repeats itself over and over again its rhythmic so that's where the name rhythmites from so Lake Missoula had several different rhythmites the first one that we see in Missoula and the surrounding areas are the barbs and these are very common in glacial lakes so in the summer when the glaciers are actively melting you have meltwater it's carrying a bunch of rocks that are ground up by the glaciers into rock flour and that rock flowers flowing out into the lake and it's getting deposited on the bottom of the lake and it makes this big thick white deposit the rock flower and then the winter comes it locks up the ice the supply of the rock flower is cut off and over the winter we deposit much less material it makes a dark band and then the next summer the process repeats itself those rhythmites are how we're trying to back out just how many times the lake actually filled and flooded when we first put out the story of Lake Missoula we thought it was one time then Jay Harlen Bretz wrote a paper not too much longer where he said it filled and drained three or four times when I was going to undergraduate school we thought it filled and drained about 20 times the current thought is that it could be anywhere between twenty and a hundred times as time goes on we find evidence of more and more floods I think the most important thing about a red might is that it is recording individual events it can be thought of much like a tree ring it records a event that is repeatable whether that's seasonal changes in a lake or repeated flooding and draining of the lake as I learned more and more I learned too understand that there were all kinds of rhythmites in nature recording these episodic flooding and receding type sequences so I learned to interpret these repeatable sequences think about history think about how long earth processes go on it really just brings out how much history Iraq can contain post your thoughts and photos on instagram with hashtag Montana Natural History Center between Missoula and Sand Point the Clark Fork River squeezes through the rugged vertical walled canyons anywhere canyon walls close in the rushing river increased speed imagine the canyon narrows or gorges as a giant hose nozzle formed by cliffs spewing 500 cubic miles of water 60 times the flow of the Amazon River along with rocks debris and silt through the gap the sheer force of the floods scoured the vertical rock faces leaving grooves in the bedrock 340 to 400 feet above the river the sheer power of the event at Eddie narrows for example is mind-boggling boulders shocked through the gorge without bouncing off the river bottom at the top of the cliff face just like cannonballs from a cannon what must it have been like the evidence left behind helps describe it Eddie Narrows is where all five arms of Lake Missoula finally came together and all the water had to flow through this point this makes it the best place to measure the flow rate and the speed of the water at the flow rate of Eddie narrows the lake could empty and about a little over two days and it determined the character of much of the rest of the flood how big the other temporary lakes were so it is really an important item to be aware of in the flood narrows are basically anywhere where you have a stream channel and that channel gets forced into a smaller area and a great analog to this is we've all taken a garden hose and when you don't have your thumb over it the water is pouring out really slowly and then when we put our thumb over the garden hose that water sprays out very fast that's because you're forcing the same amount of water through a much smaller area and so it narrows is exactly that in a stream channel we've taken a large amount of water and we've forced it into a small area and it becomes a bit like a jet nozzle and that water is forced to move very very fast in order to move the same amount of water through this small constriction and so when we have narrows that's where the white water is when we talk about narrows of glacial lake Missoula then we're talking about narrows at a whole nother scale when the lake flooded the river was about two kilometers wide or 2,000 meters wide that's a little over a mile wide so you've got to really just expand on everything you know and think that you've observed in a river at a hundred meters you got to multiply it by about a hundred so it gets about a hundred times wider and about a hundred times deeper but we're still in a Narrows so we're gonna have Rapids we're gonna have waves we're gonna get a lot of the same things we see in rivers today but they're just much much bigger almost all the roads in western Montana follow the river course and would have followed a natural drainage pattern glacial lake Missoula anywhere where you see the sides or the mountains close in on the freeway that would have been an arrows anywhere around Missoula right now you enter Albertan Gorge which is a modern-day narrows Albertan Gorge the walls of the river close in and where that happens we increase the speed and depth of the river and we get these Big Rapids and that's where people go to play in the river and get in whitewater today curiosity and imagination helped drive the scientists to interpret the ancient events and understand the present-day world a little better if you're curious explore Eddie narrows or the Albert engorge to see firsthand the power of the Ice Age flood take a selfie and post it on instagram with hashtag Montana Natural History Center you may have noticed lonely boulders littering fields housing developments and even the University of Montana campus these alien objects some as big as a car don't match their surroundings orphaned rocks called a radix tumbled in the torrent of floodwaters or carried on ice rafts caused by the release of the ice dam have been adopted by geologists as clues to ancient cataclysmic events and erratic is a piece of rock that does not belong where you find it anytime you see a large erratic or a large rock that is just sitting out in the middle of the valley on the lake sediments that's almost certainly an erratic usually they are transported by ice or on ice being pushed by the glaciers most of our erratic SAR of another kind and those are the kind that are on icebergs or in icebergs and the iceberg calves into the lake and drifts around until the iceberg either melts in the lake water itself in which it's not only an erratic but it's also an erratic drop stone or we burst the dam all the water drains out and we leave the iceberg stranded and it melts in the Sun that's the most common kind of large erratic that we have right at the corrals at the Buffalo range there is a house size erratic frame by wonderful strand lines one of the big ways to get bigger attics is to have a rock slide land on the glacier then all of those rocks that entire rock slide will get incorporated into the ice and the icebergs and they haven't been rounded at all they're as rough as they were when they were in a landslide then the iceberg will take them somewhere and drop them and they're not rounded at all we have all kind of erratic sand you have to really be thinking an erratic scavenger hunt is an entertaining way to explore the glacial lake Missoula activity find a lone Boulder snap a photo and then try to determine where it came from how far away is a rock of similar composition Montana Natural History Center is interested in what you can find in and around the Missoula Valley posted on instagram with hashtag Montana Natural History Center mega dunes quarks and scablands oh my knowing a bit of these geologic events as you travel the byways of western Montana whoo to spy other clues left among the mountain valleys as the river swirled through the narrow canyons the velocity of the floodwaters increased sediment gravel and rock tumbled in the lot a colored white water at Tarkio the river course snaked through the canyon and slowed just long enough to drop gravel in a giant dune five hundred feet above today's riverbed the rounded rocks are the size of baseballs and footballs this mega dune is the biggest pile of gravel deposited by the flood mega dunes and Gulch VLEs are reminiscent of gravel bars among many western Montana rivers rocky holes and circular ponds certainly look out of place what caused these imagine a water vortex a spinning abrasive tornado more powerful than any drill bit augering basins out of bedrock these are coax made by hydraulic whirlpools and filled with debris as the floodwaters rushed west toward the ocean water moving at 65 miles an hour almost freeway speed sped down the path of the Clark Fork River leaving behind a wounded landscape called scablands small areas of scab land can be viewed along the banks of today's River in various places to define mega dunes you think of wood or dunes and dunes are in rivers they're like ripples in a river that are usually on the order of like 10 inches high - a few feet high but in these big floods like in the draining of glacial lake Missoula mega dunes are 30 feet high 100 feet high and up to 400 feet high so they're like what you see in a stream but just on a much larger scale so glacial lake Mozilla was very deep when it was at its high stand and it drained very rapidly by the failure of the ice dam so the water was rushing through the canyons at very high speed at such a high speed that it was picking up gravel and just carrying it along in the stream the gravel wasn't bouncing along the bottom it was being carried throughout the the flood height and then as it was sneaking through the Clark Fork Canyon there were places where the velocities went down a little bit and they started depositing these dune structures well what you see on these dune structures is they're shallow on the upstream side and they're deep they're more steep on the downstream side and they're up as much as 500 feet above the river level so the normal River didn't deposit these things it must have been a deep flowing flood through the canyons that was over a thousand feet deep when I started working in the late 90s and ever since then there I'm discovering more and more things to investigate that haven't been investigated previously becoming a practiced geological observer promises delightful road trips once on the trail of clues echoing through the centuries you'll be surprised at where the tracks will take you snap a photo and post it on instagram with hashtag Montana Natural History Center the story of glacial lake Missoula is echoed in the scoured scablands west of the Missoula region the massive flood ice rafts gravel and sediment continued its frantic course through Idaho's Panhandle the barren but beautiful channeled scablands of Eastern Washington and the gorge of the Columbia River and the Pacific the devastation left behind has been compared to the surface of Mars Mars rovers have crawled the scablands simulating a Martian invasion you when the dam broke the water went downstream that means it went through Idaho into eastern Washington spilled across much of Washington and eventually funneled down the Columbia River Gorge it's lopped up in the Willamette Valley beyond Corvallis and then went out to the ocean downstream for Portland and some of that water we have good evidence that it went all the way up to Vancouver Island in the deep sea to ten thousand feet below sea surface there's sediments offshore Vancouver British Columbia that we can tie back to rocks in Montana as you travel west follow the Ice Age flood institute's geological trail snap some photos and post them on instagram with hashtag Montana Natural History Center curious geological sleuths like Jay Harlen Bretz Joseph cardi and David alt have described our home landscape by following the clues left in the soil cliffs and riverbeds of western Montana the case continues to be fleshed out by present-day detectives using increasingly sophisticated technological tools the flood ease of the Missoula chapter of the Ice Age flood Institute have developed a driving map and educational information to help everyone understand the impact of the flood and the story of the land in the Missoula region the driving route is part of the larger Ice Age floods geologic trail the trail is a network of routes connecting interpretive facilities about the path of the Great Flood and is the first of its kind in the u.s. from the first indigenous people living on the land to today's students and scientists curious people have been asking questions observing the phenomenon and slowly filling in the story of how our landscape was formed and what we might learn about the future a lot of people have heard of carbon-14 dating where you can date bones you can date teeth and you can date burned wood unfortunately you don't find any of that in the glacial lake Missoula section and so there's a new technique you can date the last time courts or feldspar was exposed to the Sun and so it builds up a changes it's in its structure by natural radiation from the sediment around it if you bury it and then when you expose it to the Sun it luminescence ever so slightly and so that's what I've been using to date both the silt beds of the glacial lake deposits and now dating gravels for when the gravels were buried water is the most important thing at the surface of the earth that shapes the earth so when we look at rocks were actually what we're really doing is looking at the history of the hydrology of that particular area and so when we look for this evidence of glacial lake Missoula what we're looking at is it is records of how the water at that time was shaping the landscape and those records are left behind when the water left the story of glacial lake Missoula is not fully written yet be a part of the saga be curious and be amazed by what is in your own backyard there are hundreds of phenomena still undiscovered out there find some take a photo get the GPS coordinates and post it hashtag 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Length: 30min 59sec (1859 seconds)

Published: Mon Jan 20 2020