The Mysteries Of North America's Great Lakes | Naked Science | Spark

of all the world's drinking water 1 fif is stored in one place the Great Lakes they're so big they're like Inland Seas so vast they make their own weather without them a large part of North America would be arid they're filled with enough water to flood the continental United States 9 ft deep but water levels are changing dramatically to understand where the waters are going you have to know where they came from and unlock the Mysteries behind the Great [Music] Lakes [Music] the Great Lakes deserve their name they cover an area bigger than Utah and hold 5,500 cubic miles of fresh drinkable water the deepest of the five lakes Lake Superior is over 1300 ft deep Lake Michigan and Huron provide drinking water for over 10 million people in Chicago and Detroit between Lake Erie and Ontario is the mighty Niagara Falls at its peak over 40 million gallons flow over the falls every minute it provides electricity to roughly 5 million homes the Great Lakes are unique but how did these five vast lakes form what force was so powerful it reshaped Solid Rock and carves such deep depressions beneath a sea of water and silt the Lakes cover up the evidence of their Origins yet on an island in Lake Erie one clue is [Music] exposed Kelly's Island sits on Ancient Rock The Rock is scarred by strange grooves some more than 15 ft deep and 400 ft long if we were to peer into the depths of the Lakes down to the Bedrock this is what we would see Dr Jeff dick from Ohio University is looking for Clues to how the lakes formed the groove that we're sitting in here provides a very interesting tidbit of information as to how the great lakes formed the area that we're in this groove was obviously gouged out by some Force but which force carve these Lakes one of the Earth's most dramatic sculptures is volcanism boiling hot magma erupts from deep within the Earth as it cools and hardens it can produce incredibly strange geological formations did volcanism do it the rocks at Kelly's Island hold the answer tiny Coral fossils when Rock melts the fossil record is usually destroyed if lava had formed the grooves these fossils would probably have been [Music] erased the next suspect is water if water carved the Grand Canyon why not the Great Lakes but water has an alibi fractures in the Rock if it had been formed by running water a stream a river it's more than likely that that streamer River would have taken advantage of this weakness in the Rock and actually followed it meaning that the fractures would direct where the stream flows and in this particular case the grooves are running almost perpendicular to them suggesting that maybe there's another Force at action here so if volcanism and running water didn't shape the grooves what did there's another suspect [Music] ice but how does mere ice carve Stone where better to find out than Earth's most spectacular Frozen landscape Iceland this is the vat neok Glacier it's the largest sheet of ice in Europe it covers 3,200 square miles that's more than twice the area of Rhode Island in places it's over 3500 ft thick geologist Andy Russell knows it like his backyard this Glacier although it may look as if it's sort of sitting there and uh you know fairly passively the actual ice is always moving forward even though the edge of the glacier may be stationary this time-lapse footage shows the glacier's movement speeded up hundreds of times behind the Leading Edge the ice moves up to 3 ft per day with a heavy the step a glacier a mile thick exerts about 2,000 lb of pressure per square in that's the weight of 115 cars on one square foot of land for all its bulk ice isn't as tough as it looks to cut into Solid Rock and form the basins of the Great Lakes ice needs another ingredient Andy Russell demonstrates I shall take a bit of ice which has a smooth surface and we'll drag it across the tin foil really there's very little damage to the the tin foil so we'll now move on to the uh the dirty ice dirty ice is embedded with small rocks and stones we can see it's got all this uh grit on it and we're going to see what it does to the the uh tin foil the tin foil is being shredded that's how a glacier does damage as it travels the glacier picks up stones and rocks the weight of the ice holds them against Bedrock then the moving Mass scours the land like a huge sheet of sandpaper when the glacier finally melts it leaves behind a vast depression filled with glacial meltwater normally it's impossible to see glacial erosion in action the process is hidden beneath a blanket of solid ice but here in Iceland the base of the glacier is exposed it shows Russell just how ice grinds through solid rock and explains how ice could carve the Great Lakes we've got layers of ice which you can see in here mixed with layers of debris or it's dirt here and also here and obviously this big bit of uh Rock here this Boulder the boulder tells us several things all these little scratches crisscrossing and the fact that this surface here is extremely flat tells me that that Boulder has actually been at the glacier bed it's been uh held in the ice and then it's been ground round against the Bedrock this Glacier is melting and as it melts it drops its load Iceland is littered with thousands of dropped [Music] rocks it's this action of rock grinding against Bedrock that may have gouged out the strange grooves on Kelly's Island but where's the proof that a giant Glacier passed over the Great Lakes [Music] area here near the shores of Lake Ontario scientists call this an erratic Boulder meaning it doesn't belong here this giant boulder is made from granite a type of rock not found within 100 miles of this area like the boulders in Iceland it was trapped inside ice for thousands of years dragged across the Bedrock and and then dropped in its new home the glacier that moved the boulder must have been enormous the proof again lies in the rock of Kelly's Island from the chemical makeup of microscopic fossil shells scientists can tell the water was once much colder tiny Clues lead to a vast conclusion a glacier up to 2 mi thick covered most of Canada and a large part of the US it was called the laurentide ice sheet for over 1 million years the enormous Glacier Advanced and retreated over the land back and forth as it did it gouged out the five enormous Lake basins the ice sheep passed over the Great Lakes but how long did it take for ice to carve through solid rock and form the basins of the Great Lakes geologists think that the Lauren tii sheet moved across North America for over 1 million years but how long did it take to gouge out the five vast Lake basins in Iceland the vokal glacier erodes Bedrock just as the laurentide once did in the Great Lakes Andy Russell measures the groundup rock washed away a sediment this equipment uh measures the cloudiness of the meltwater the cloudiness of the water gives us a a sediment transport rate in the river and if we average that and scale it up over a longer time spans we can figure out how rapidly the uh catchment is eroding measure the sediment produced average it up over time and this Glacier grinds away around 1T of solid rock every 100 years but did the laurentide erode rock at the same rate it was after all over 1,000 times bigger than the vokal glacier John men has come to Mohawk Bay on the shores of Lake Erie to find out the answer lies hidden in these Cliffs they look like mud but they're ancient Rock sediment this was once solid Bedrock it was crushed by the laurenti ice sheet and deposited here based on the evidence we're trying to sample here today and we hope that this will illustrate how the Great Lakes basins were formed and developed these tiny Rock particles hold a secret menz sets the sample in resin and slices it into thin sections normally glacial erosion produces rock grains with Jagged edges these grains are nearly round if you look at this particular thin section you can see this particular piece of rock and you can see around it the effects of rotation kind of indicative of the sediment being moved underneath the ice sheet and rolling and rotating beneath the ice so in other words the sediment has been tumbled and moved and rotated and sheared time and time again but how can a glacier produce both Jagged and smooth rock grains the explanation some of the ice inside the laurentide glacier moves faster than other areas of ice [Music] the fast moving ICE is called an IC Stream Ice streams are like rivers of super cooled water water that's well below freezing but doesn't solidify these Rivers can flow up to 3,000 ft a year 10 times faster than the surrounding slow solid ice working 10 times faster they can potentially dig 10 times deeper more proof that the Lauren tide contained fast ice lies beside Lake Ontario this is an aerial photograph of the shoreline it shows strange elongated Hills these are lumps of sediment called drumlins as the glacier retreated they were left behind here's how they formed I think that's an interesting thing this one piece will make 52 layers watch on mobile devices or the big screen all for free no subscription required so if we produce a blob of toothpaste and this we take as the base of the ice and so as the nice deforms so does the toothpaste deform and we produce this nice linear you can actually see the small lineations Drumlin likee Streamlight forms that are actually been produced simply by moving one interface over another interface just as fast ice leaves a trail of long thin drumlins it also tends to carve out long thin Lake basins if fast ice alone carved the Great Lakes it could have taken as little as 100,000 th000 [Music] years the ancient ice sheet gouged out millions of tons of rock grounded into fine sediment carried it away by meltwater and flushed it out into the Atlantic Ocean left behind Five enormous basins the deepest lake Superior more than 1300 ft the Great Lakes but when did the enormous laurentide Glacier melt and the basin's fill with lifegiving fresh water Francine McCarthy holds a clue a 12T tube of mud called a sediment core the sample was taken from the bottom of Willow be bog a swamp between Lakes eerie and Ontario this keeps a very good record of what went on when people weren't here to keep the history the core is made up of mud pollen grains and sediment deposited in the water when the lakes formed we remove material for radiocarbon dating and the dates are about 1700 years ago here about 7500 years ago here and about 9,000 years ago near the base the cores reveal water was present at least 9,000 years ago but beneath the 9,000-year old layer is one even older it's the last layer before hitting Bedrock so it must be the first layer deposited in the water if McCarthy can date it she can pinpoint when fresh water arrived and reveal the the age of the Lakes but to date the layer she needs organic material you can see the color contrast between the very inorganic and the bog material this is impossible to date using radiocarbon dating conventional radiocarbon dating techniques because you can see that there's very little organic material here just rock and Clay a dead end but why are the early Lakes lifeless to find out what the early Great Lakes looked like we need to return to Iceland and the vokal glacier here at the base of the glacier is a newly born Lake its Basin was carved by ice and filled with meltwater this is how the Great Lakes looked tens of thousands of years ago and like the early Lakes this place is dead there was virtually no life in these proglacial Lakes it's very cold it's very harsh environment there's very little light so your whole ecosystem is unable to really get kick started the reason the water's strange milky color these Lakes are loaded with groundup bedrock sediment washed down from the glacier this sediment blocks out light and without light small organisms like algae can't survive no plants no food no life as the voko glacier continues to melt more water will flood this Lake and dilute the sediment eventually it will settle on the bottom just as it did over thousands of years ago in the Great Lakes this is the pale gray layer McCarthy discovered the mystery remains scientists have to find some other way to date the age of the Lakes the answer could lie hidden in one of North America's most spectacular geological formations Niagara Falls Niagara is the mightiest waterfall in North America and one of the great lak's most awesome features on average 150,000 gallons pour over every minute enough to fill over 60 Olympic siiz swimming pools Niagara holds the answer to a prehistoric mystery when did the Ice Retreat and the Great Lakes fill with water John men has come to investigate it's the first time he's gotten this close to the falls it's just utterly incredible if you see the volume of water is coming over per second all the water from the central part of North America is Flowing right over here as we stand fantastic it's possible to date the arrival of the water in the Lakes because Niagara behaves very strangely The Falls are moving every year they take one step back 12 full inches toward Lake Erie the reason for this movement is The Rock The Falls are built on two layers of rock at the top of the falls is a hard layer of limestone known as capat rock underneath is a softer layer this is a piece of Queenston shell which is the weaker Rock from underneath the cap Rock for this Area Regional geology and in fact it's very very easily to break as you can see Bingo the weak Shale at the base of the falls is relentlessly pounded at up to 70 mph the constant hammering erodes the Shale below and undermines the cap Rock above the c rock gets left like a cal lever effect and then it simply breaks off and it breaks off every so often fairly dramatically in fact if we look at the Falls there's a huge Rock that's actually fallen off in the last 100 years in a sense you can look at Niagara Falls as being if you like an ongoing process of Destruction Perpetual destruction Perpetual change the destruction means that the Falls act like a giant time piece an enormous CL clock that allows geologists to date the age of Niagara and the lakes themselves until 100 years ago the Falls eroded 3 to 4 ft a year as water was diverted for hydroelectric power the erosion rate has fallen but the Falls are still eroding roughly half an inch a month eventually given time the hotels the casinos and so forth are going to be left behind in the track of the falls as the Falls retreats to the and leaves this this touristic area in isolation if the Falls continue to erode at this rate in about 50,000 years The Falls will reach the base of Lake Erie [Music] itself as the Falls retreat they carve a giant Canyon the Niagara Gorge 3 m Downstream from Niagara geologist Francine McCarthy can date the Great Lakes by searching for the Fall's birthplace the secret is hidden not in rocks but in clam shells well that's that's perfect we can identify that to species it's definitely the kind of thing we want to radiocarbon date back at the lab this species of mollusk lives in Lake Erie it was carried down river and over the falls the surging water wedged the mollusk into cracks at the base where it died the Falls moved on the shell remained by carbon dating shells like this McCarthy can prove Niagara Falls roared over this exact spot 7,000 years ago the water level would have had to have covered this area in order to deposit the little aquatic clams in the crannies where we find them further proof can be seen in the strange rocks scattered around this whole area these holes were cut into the Rock by the constant pounding of water over the falls but this isn't niagara's birthplace the further McCarthy Walks from The Falls the further back in time she travels and the older the shells she discovers by analyzing shells found All Along The Gorge McCarthy reveals the life cycle of the Lakes from niagara's spectacular location today to their location in 1678 when the first written account was made Downstream to the whirlpool Rapids 5,500 years ago through Niagara Glenn where McCarthy shells reveal their location 7,000 years ago to Queenston 10,500 years ago and finally 7 m Down River from The Falls where a natural Ridge called the Niagara escarment cuts across the land scientists discover the oldest shells yet the Niagara Falls are 12,600 years old they've been operating since Water started melting from the laurenti ice sheet and if Niagara Falls is 12,600 years old then the laurentide glacier must have retreated at least 12,600 years ago exposing the two Lower Lakes Erie and Michigan the mystery is solved like Niagara the Great Lakes have continued to evolve over the Millennia but some changes happened much more dramatically than anyone imagined today rainfall on Lake Superior takes 204 years to travel through all the other Lakes before it reaches the Atlantic Ocean more than 2,000 M away the Great Lakes flow East and always have or so geologists thought scientists studying fossils in the Gulf of Mexico uncovers surprising species it forces them to re-evaluate what they thought about the Great Lakes scientists analyzing 14,000 yearold shells discover the water in the Gulf of Mexico must have been less salty than today but why only one source of fresh water was vast enough to dilute the gulf the laurentide glacier fossil records suggest the m mwat drained South along the Mississippi River to the gulf but then nearly 13,000 years ago some Titanic Force diverted the flow from South to East the question is what force was powerful enough to divert the Great Lakes 13,000 years ago some unknown Force diverted the flow of meltwater from the laurentide glacier geologist Alan West searches for answers on the shore of Lake Michigan uh this is a visual line that's actually where our greatest interest uh lies the great legs really began right at this line in the sediment West finds tiny specs the size of sesame seeds they're made of carbon West believes they're all that remains of a vast Forest incinerated at sizzling temperatures but the most important clue lies inside each grain a dazzling secret these small black dots they're almost pure carbon and when we check them with an electron microscope we find that they contain millions and millions of diamonds each diamond is a thousand times smaller than a pin head they're known as impact diamonds they form under intense pressure but what created them something big hit this area at great speed it packed a huge punch Allan dumps a sample over a magnet incredibly it contains metal definitely magnetic grains in there you can see them coming out the magnetic grains are iridium iridium is extremely rare on Earth but common in rocks from space West's theory is 12,900 years ago a massive Comet strikes Earth and showers the region with iridium wildfires sweep across the area and destroy all vegetation the sh wave breaks up part of the laurentin glacier billions of gallons of water are released it's well known that when these meltwater Outburst floods occurred they're very very abrasive they can change the shape of valleys they can scour Bedrock so it's entirely possible that they dug the Great Lakes deeper or at least remove sediments that were already there thousands of tons of rock soil and debris are flushed South like a giant plug it blocks the Mississippi the water backs up Lake Ontario swells and bursts its low Eastern Bank and the St Lawrence Channel opens up all the evidence shows that Gulf of St Lawrence opened up and water went to the east but stopped going to the South West believes it all happened in just a few months since then the Lakes have drained East into the Atlantic Ocean the New Direction allowed small settlements to become the great cities of Montreal and Quebec rarely does the course of history change so suddenly and so dramatically yet the evidence is circumstantial if a comet hit where's the crater in 1999 on the bottom of Lake Ontario geologists discovered a crater half a mile wide it's still undated West believes it might be a fragment of the Comet that diverted the water no other craters have been found but West isn't surprised the comet could have done its damage and simply melted away because comets are mostly ice this is the perfect crime the ice bullet shoot someone with an ice bullet and you can't tell who did it Earth got hit by an ice bullet actually thousands of them and so the evidence is minimal as the last ice age ends all five Great Lake basins are slowly revealed and filled with fresh [Music] water but there's one huge difference between these early lakes and the ones we see today they aren't linked to unite them we take a force of nature more powerful than a comet today the Great Lakes are connected via a network of rivers and channels a 2,000m water system this wasn't always the case the upper Lakes Superior Michigan and Huron weren't always connected to the two Lower Lakes Erie and Ontario Francine McCarthy is trying to find out how they joined we've taken some samples all along the shoreline of Lake Ontario and lake eie and we're going to look under microscope at small seeds and pollen to find out the age of the samples and what kind of environment they were deposited in 5 miles Inland from Lake Erie McCarthy discovers a tiny clue wild rice this is incredibly strange wild rice doesn't grow Inland wild rice needs to have sort of agitated well oxygenated water in order to be happy the fact that there was a lot of wild rice indicates that the water level in Lake Erie was higher than it is today Lake Erie must have been much bigger and more turbulent the wild rice date of 4230 years tells us that water levels Rose quickly instantaneously in both the area and Ontario basin but why McCarthy has a theory over 4,200 years ago Lake Huron swelled and burst its Southern Bank a torrent of water pushed South Lake Erie suddenly expanded and wild rice took root in its Disturbed Waters the St Clair River opened and the lakes joined that's when we begin to see the truly modern conditions since 4200 years ago there's never been any other way for water to flow out of the upper Lakes but through the St Clair River into Lake Erie over the falls and into Lake Ontario but why did hurons swell and flood South the mystery deepened when scientists know notice something strange happening in the Great Lakes in each Lake the water level in the north is falling but in the South it's rising what mysterious force is behind these strange phenomena Professor Doug Hunter and divers Luke kurn and Kathy trackx are plunging into the lak's past to find evidence of ancient water levels they start their investigation in Lake huron's southwest corner in the Harbor Town of Lexington they need evidence to show whether this imbalance in water level is a recent phenomenon or if it's been going on for Millennia today we're going to put divers in the water and as we dive down we're looking to see if we can find something that will show this this is where the lake levels were some thousands of years [Music] ago Lake Huron is over 700 ft deep in places but the area the team are interested in is only 40 ft deep right now we're about 2 and 1/2 miles east of Lexington Harbor underneath us in 40 ft of water is uh an area where we suspect there may be some interesting finds that would give us some uh insight into the Great lak's history this section of the lake bed has never been surveyed the team scour every inch for evidence of past water levels they're looking for something out of place some clue to this strange mystery 40 minutes into the dive the team finds several large lar pieces of wood from this wood alone they can't tell if trees once grew here or if it's just debris thrown from a boat they need evidence like this a tree trunk it's still rooted in the lake bed these stumps have never been seen before this proves that trees once grew in this exact spot a true Discovery there's wood boy that was a great dive you can see whole trees falling over and they just went out into the sand and down but once we found the tree stops and you could see the the roots of the tree stops running down it had to be Shoreline this part of Lake Huron was once a forest of Cedar and pine today you have to dive 40 ft to reach the trees but once you could have walked here and not even gotten your feet wet when could you have strolled through the trees these stumps have to be carbonated but samples from other locations in the lake have already told their age we discovered that the most recent one was 6,400 years before present um the oldest one was about 7900 years before present so it's quite a long range quite a large range of dates 6 and a half thousand years ago Lake Huron was a fraction of the size it is today a forest flourished on its southern end 1500 years later water crept South the southern end was swamped and the forest drowned [Music] the St Clair River opened and Lake Huron joined to Lake Erie the Overflow thundered along the Niagara River and tumbled over the falls and all five lakes joined but what caused this dramatic transformation and is it still taking place today [Music] Mike Kramer from the geologic survey of Canada is investigating a strange anomaly why water levels in the Great Lakes are dropping in the north and rising in the South Kramer works on a remote spit of land next to Lake Ontario it's not the water level he's monitoring what looks like a garden shed actually holds state-of-the-art GPS technology we're using a GPS receiver to monitor the motion of the structure every 30 seconds the antenna is bolted down to the floor and runs up through the roof it's uh very stable in other words Kramer is studying whether the shed is rising or falling this GPS receiver picks up signals from satellites orbiting the Earth the equipment is so sensitive it can detect movement down to the millimeter as a result Kramer can determine the exact elevation of the shed and thus the land it sits on his findings are astounding the Great Lakes region is Rising 1 in per decade in the north and sinking nearly 1 in per decade in the South this part of North America is tilting and the Pivot Point runs straight through the Great Lakes the Tilt is imperceptible to us but it affects the Lake's water level we have a bowl of water representing a lake uh this end being the north this end being the South and if we can imagine as the land tilts the water levels are rising in the South and falling in the north it appears as all the water level is falling and actually it's a land that's [Music] Rising the changing land levels are tiny but over time all those inches add up ultimately tilting is what drowned a forest but what force is powerful enough to tilt a major part of the North American continent scientists think it's the opposite of the force that compressed it Earth's surface can actually be squashed if the weight is heavy enough few forces are capable of compressing the crust one is ice the laurenti glacier weighed around 10 million billion tons once it reached a certain thickness the glacier depressed the crust 1 ft for every 3 ft of ice it left a dent up to a half a mile deep about uh 20,000 years ago the ice had covered most of Canada and uh the great weight of that ice had depressed the crust substantially and as the ice retreated and melted the land underneath it then began to rebound rebound began as the ice melted tens of thousands of years ago and continues to this day about a tenth of an inch per year [Music] the ice sheet was much thicker in the north than it was in the south at its thickest it compressed the Earth the most so when the weight was removed the Earth rebounded more in the north this imbalance causes much of North America to [Music] tilt combined with a warming climate and less rainfall rebound is changing the outline of the Great [Music] Lakes if water levels continue to drop in the north vital transport routes will shrink industry hydroelectric power stations and millions of people could be affected eventually the crust will rebound to roughly the position it was before the laurentide glacier Advanced over it and the water will find its level but until it does the future of the Great Lakes will be as dynamic as their [Music] past [Music]

Channel: Spark

Views: 1,407,342

Keywords: Climate change, Documentaries online, Documentary series, Earth science, Ecosystem, Educational documentaries, Environmental education, Environmental stewardship, Freshwater ecosystems, Geography, Global water supply, Lake Erie, Lake Huron, Lake Ontario, Nature preservation, Planet Earth, Science and technology, Spark, Water levels, Water pollution, Wildlife habitats

Id: _keDwFgt8W8

Length: 45min 59sec (2759 seconds)

Published: Fri Mar 15 2024