"Deep in the pennsylvania woods." "Lies a dark secret From america's industrial past." "I think we found A mass grave site." "Is this where dozens Of missing laborers." "Were secretly buried?" "And were their deaths accidental Or foul play?" "I'll use advanced imaging Technology to investigate." "There it is." "And in southwestern virginia," "The filming location Of the iconic movie." ""Dirty dancing" Is steeped in mystery." "My gosh." "Look at that." "What caused a 47-acre mountain Lake to suddenly disappear?" "We were devastated." "We didn't know what to do." "I'll use a new seismic test To find out." "Whoa!" "Hidden just below The earth's surface," "There are countless Unsolved mysteries." "And, today, we finally have The tools to unlock them." "Look at that!" "Whoa." "I think this is it." "I'm rob nelson," "A scientist using State-of-the-art technology." "To peel the lid off Our planet's hidden depths." "The moment of truth Right here." "Holy moly!" "These are the secrets Of the underground." "Captions paid for by Discovery communications." "In chester county, Pennsylvania, 20 miles west Of philadelphia." "Lies a stretch of forest That is said to harbor." "A dark secret of america's Industrial past." "According to locals, this area Is the site of a mass grave," "The final resting place Of dozens of irish immigrants." "Who mysteriously perished In the 1830s." "And whose deaths Were suspiciously covered up." "By authorities." "Were they innocent victims Of disease," "Or is there a darker side To the story?" "I'm heading to southeastern Pennsylvania to investigate." "With the latest high-tech Imaging tools," "We can now see through the soil." "Like never before And, hopefully," "Locate the other bodies." "Today, the only remembrance Of the victims here." "Is a memorial stone wall." "That was erected by A later generation of workers." "Who heard about their deaths." "This is where I'm meeting local History professor bill watson." "To find out more about The workers who died." "So these stories Go back a long time." "What evidence do we have Of a mass grave site?" "Well, for years, It was just folklore," "Not knowing whether there Was any substance to the legend." "As a local irishman, bill was Always interested in this story." "But in 2002, his fascination Took a very personal turn." "When he and his brother Came across a stash." "Of long-lost documents." "This is The pennsylvania railroad file." "On the story Of the mass grave." " Can I see this?" " Yes." "Absolutely." "My grandfather worked For the man who assembled this." "The papers tell Of the construction." "Of one the country's oldest Commercial railroads," "The 82-mile philadelphia And columbia line." "So this whole thing Goes back to an incident." "That happened when The railroad was built?" "And what we know here Is that a total of 57" "Irish railroad workers Were involved at the time." "In the biggest Industrial endeavor." "In north america, Actually..." "The philadelphia And columbia railroad." "And we're at the site Of the most difficult mile." "In that entire system." "In 1832, A contractor named philip duffy." "Set out to construct Mile 59 of the line." "The area's hilly terrain." "Made it one of the railroad's Toughest stretches." "To build what came to be Known as duffy's cut," "He hired dozens of laborers Right off the docks." "They were among the tens Of thousands of irish immigrants." "Who arrived that year," "Desperate to escape The destitute conditions." "In their native land." "But within weeks Of reaching their new home," "It said that the laborers All died." "During a cholera outbreak That swept through their camp." "Legend has it their bodies Were then dumped." "Into a mass grave near mile 59." "Yet, strangely, even though." "The confidential company files." "Reveal that 57 workers At duffy's cut died," "Newspapers at the time reported The total number of deceased." "Was only 8." "If disease was to blame," "Why were so many of the deaths Kept secret?" "So this particular document Points to 57 people dying here." "But that leaves 49 bodies That are missing." "Where are they?" "And why would they have tried To cover up this incident?" "That's a good question." "We intend to find out." "To help us search For new clues," "We're bringing in bill's Brother, frank watson," "And geophysicist tim bechtel." " Hey, tim, frank." " Hey, guys." "The three made A stunning discovery here." "A few years back Using ground-penetrating radar," "Or gpr." "While mapping the area's Subterranean structure," "They hit upon Something strange." "We found an anomaly right here At a very resistive blob." "Down inside The embankment." "That anomaly turned out to be The remains of eight laborers," "Presumably the ones whose Deaths were made public." "And you found eight bodies?" "We found the... the six..." "Six bodies and..." "And another coffin." "And then a stain of a coffin." "More of a stain." "Yes." "The find reignited The long-forgotten mystery." "And offered Breakthrough forensic evidence." "That could reveal, For the first time," "How these workers died." "Bill and frank explain How a letter." "From their grandfather's Secret files." "Led them to the graves." ""They were buried were They were making the fill."" "penned by the son Of a former railroad employee," "The note suggested The mass grave." "Was hidden In the raised bed of soil." "That was built for the tracks." "We realized, "Wait a minute."" "These guys are In the embankment."" "At least eight of them were." "But there was no trace Of the other laborers." "Whose deaths were kept quiet." "So what I don't understand Is you've got eight bodies." "Those were ones that You said were in coffins." "So where's The other 49 bodies?" "We have a suspicion." "Tim believes the answer to the Mystery goes back to the 1870s, 40 years after the deaths," "When the rail line was improved For modern trains." "So to take this curve out," "In 1870, they moved The railroad bed." "Just a little bit To the north." "And, of course, To build that bed," "The easiest material to use Is the 1832 material." "Stuff that was already loose." "This is already loose." "It's been dug." "So you dig this out And move it over." "Tim suspects that the laborers." "Stumbled across all 57 bodies." "While digging into The old embankment." "The workers would've found Eight of the bodies in caskets." "And it seems they Left those untouched." "So those eight were buried in A proper irish catholic fashion." "They were in coffins." "But tim thinks That out of respect," "They reburied the others Somewhere else." "But where?" "Is that what I think it is?" "Will our high-tech tools Finally reveal." "Where the bodes Were secretly stashed?" "Is that it?" "If so, we'll be One big step closer." "To figuring out exactly how These workers died." "And why their deaths Were never reported." "Were they just victims Of disease." "Who were swept under the rug?" "Or is there something More sinister to this story." "That could point to a dark Chapter in america's past?" "You're saying there's evidence This probably wasn't cholera." "No." "And later, I'll head To the blue ridge mountains," "Where an iconic landmark Made famous." "By the film "Dirty dancing" Has suddenly disappeared." "This, right here, Is a little section of water." "That remains of this lake." "To investigate, I'll send an r.O.V." "Into what's left of The vanishing lake in attempt." "To solve this Perplexing mystery." "My god." "My god!" "I'm exploring a stretch Of woods known as duffy's cut," "Where 57 irish railroad workers Mysteriously perished." "So far, a team of historians." "And scientists Have recovered." "What appeared to be remains Of the eight laborers." "Whose deaths were reported In the papers." "Geophysicist tim Bechtel suspects." "That in the 1870s," "The other 49 were Reburied elsewhere." "To make room For a new set of tracks." "And they hit the mass grave." "And that would've Freaked them out." "If we can figure out where The missing men were moved to," "Maybe we can find new evidence." "That will tell us How they died." "And why their deaths Were covered up." "The grave may be Too deep for gpr." "To accurately detect it." "So we're turning to electrical Resistivity tomography," "Or e.R.T., which can penetrate To greater depths." "Tim and his assistant, marian," "Set up their e.R.T. Gear Near the memorial wall," "Which was erected in honor Of the workers decades later." "Tim thinks it could Mark the spot." "Where the lost victims Were reinterred." "Put 'em on the bottom side?" "Anywhere, as long as there's Good metal-to-metal contact." "With e.R.T., a current Is injected into the ground." "Between a set of electrodes." "Okay." "That's set." "And now, we have this grid Of electrodes covering." "This whole area All connected by cables." "We have 56 electrodes." "Yes." "And we want to send Electrical current." "Between every Conceivable pair." "By analyzing how The electrical pulses travel." "Between various points," "We can build a picture of how Resistive the ground is." "And identify any anomalies that Could be signs of a mass grave." "We send currents through In all different directions," "Just every pattern Conceivable." "And then we're going to be able To calculate from that." "The distribution Of the electrical resistivity." "In the earth." "This is a great way To peer beneath the soil." "But tim suspects that even." "If this is the location Of the mass grave," "We may not find any bodies." "Because if the 49 workers Were dug up." "And reinterred decades After their deaths," "They may have fully Decomposed by now." "During that period, they're Exposed to the atmosphere," "To moisture and oxygen." "So that's going to start." "The decay process All over again." "So we're also searching For cavities of air." "Where the remains Could once have been." "Because the ground should've Hardened around the remains." "And kept its shape." "As it decays and collapses," "It's probably going to leave Some airspace behind." "Right." "Big electrically Resistive blob." "Currents flow easily Through damp soil." "But are resistive when passing Through large voids." "Okay." "This is showing us the positions Of the electrodes." " But, I mean, this is raw data." " Yeah." "We don't know anything About the subsurface." "But then it's very simple Because what we can do." "Is run the algorithm." "The data collected From the currents creates." "A detailed 3-d map Of the ground." "This color scale is Showing its resistivity," "Red being resistive." "This corner is over here." "And this corner Is over there." "So resistive..." "We've got a resistive blob." "Right there." "Right there, there's something." "And that blob looks a lot." "Like a large air cavity In the earth," "One potentially large enough To contain a mass grave." "Let me count in From the electrodes." "And it looks like it's gonna Be two or so in." "Yeah." "It's right about here." "Holy moly." "There's a very large Resistive mass 20 feet down." "That's, like, almost 20-feet-by-20-feet." "Yeah." "And it... it needs To be big for the remains." "Of 49 humans." "It's a geophysical anomaly That's perfectly consistent." "With what we're looking for." "The site lies on private Railroad property." "And we can't get Clearance to dig." "Because of its close proximity To an active rail line." "So we won't be able To confirm for sure." "Whether this is the site Of the mass grave." "But I can still investigate The broader mystery." "Why would railroad officials Try to conceal these 49 deaths." "Unless they had Something to hide?" "According to the company's Recently unearthed secret files," "All 57 workers perished From cholera," "A bacterial infection That causes kidney failure." "And severe dehydration." "Cholera is typically spread Through tainted food and water." "If left untreated, It can kill within hours." "Cholera epidemics were prevalent In the united states." "During the 19th century." "But improvements in sanitation." "And medical treatment Have made it very rare today." "So is disease the real culprit Behind these deaths?" "Some believe that story Just doesn't add up." "We rescanned the area," "And I think we found A mass grave site." "Physical anthropologist Janet monge." "Has closely examined The remains of the few." "That have been recovered From duffy's cut." "And she's skeptical That all 57 workers." "Who went missing could've Succumbed to the same illness." "In the 1830s, cholera's Fatality rate was about 60%." "It really cannot be spontaneous, Simultaneous death." "Of all 50-plus people From cholera." " Right." " It... it can't be." "Or it would have A mortality from cholera." "Which is not matched Anywhere else in the world." "In fact, janet suspects There may be." "A more sinister explanation For this mass death." "The issue is, though, How did they actually die?" "The real sort of powerful Bit of data." "Is that all of the individuals That we excavated." "Had blunt-force trauma." "Or actually Bullet-based trauma." "What really happened To these 57 workers?" "Using ct scans, We'll take a closer look." "At the recovered remains In the search for new clues." "About the dark secrets Of duffy's cut." "I'm investigating The strange case." "Of 57 irish immigrants." "Who mysteriously perished While building a railroad." "At pennsylvania's duffy's cut." "Internal company reports claimed That cholera killed them all." "But physical anthropologist Janet monge suspects." "There's a more Disturbing explanation." "Most of the bones that were Exhumed at duffy's cut." "Have now been properly reburied." "So janet pulls up Reconstructions." "Produced from ct scans." "One of the skulls shows A very distinct hole." "We found metal fragments Inside of the skull." "No way!" "Really?" "So we do know that it was A bullet hole." "Absolutely." "And this is, actually, Probably an ax wound." "Janet sees compelling evidence That they were inflicted." "While the victims Were still alive." "After the person was dead," "This would've Shattered the skull." "But, no." "This is just broke the skull," "Like you would break A living tissue." "Bone is actually Kind of elastic." "Right." "It's 40% collagen." "So when someone's Hit on the head," "And the person is alive..." "Whoa." "The bone actually doesn't Fracture or fall apart." "It distorts." "The real sort of powerful Bit of data." "Is that All of the individuals." "That we excavated Have blunt-force trauma." "Or actually Bullet-based trauma." "Wow." "You know, when you start to look At those kinds of outcomes..." "Right." "Then the chances of this Being a random accident." "Or anything like that, Of course," "Becomes more And more remote." "This is a stunning Development..." "Physical evidence of A mass murder in pennsylvania." "That was never reported, Much less prosecuted." "But who would kill These laborers and why?" "It doesn't benefit The railroad to kill them." "Actually, they would Want their workers." "Yeah." "I'm sure It wasn't railway people." "It was locals in the town." "As janet explains," "The gaelic-speaking Irish immigrants of the time." "Were often treated As unwanted strangers." "Basically, What's happening." "Is these irish folks Come into town." "They don't speak english." "And they're also foreign In their religion." "They're catholic." "And this is, you know," "A time when There's lots of issues." "Between protestants And catholics." "But was mere intolerance enough Of a motivation for mass murder?" "It seems like there has To be more to the story." "Piecing together the evidence From the recovered remains." "And historical records," "Janet and others have Come up with a theory." "When a cholera epidemic Swept through their camp," "Some of the immigrants May have tried to escape." "An imposed quarantine." "But they were intercepted And killed by local vigilantes." "Trying to protect the community." "From the spread of the disease." "The thinking is, "Go after the intruders."" "They don't know The nature of disease." "There's no sense Of how it's transmitted." "You suddenly get sick." "So why not blame it, Basically," "On the new guys in town?" "An ax wound Is an intense wound." "Yeah, Super-violent crimes." "Janet believes the eight victims Who may have tried to flee." "Were brought back in coffins To duffy's cut." "But what about those other 49," "The nameless dozens whose deaths Were swept under the rug?" "Janet believes they probably Perished soon after." "But without their Physical remains," "We may never know whether They were victims of disease," "Murder, Or a combination of both." "Based on what she's seen In the existing skulls," "Janet suspects these men Were all murdered, too," "And that railroad officials Covered up the killings." "To protect their efforts To recruit more cheap labor." "Because they absolutely Have a mandate..." "Build this part of the railroad For x amount of dollars." "In x amount of time." "The story of these workers Was a tragic circumstance." "And a dark, lost chapter In pennsylvania history." "And though we may Never know for certain." "What really happened To the workers," "Janet and the others Who've worked to crack the case." "Take some comfort in knowing That after nearly two centuries," "Their efforts have brought This long-forgotten story." "To light once again." "It's really A tribute to them." "They died doing hard work," "Doing their job, And making america." "I mean, these are the people That made america." "Now, from this hallowed ground Outside of philly," "I'm heading south." "To the blue ridge mountains Of virginia," "Where the filming location Of an iconic movie." "Is steeped in mystery." "It was a lake used as a location In the iconic film," ""Dirty dancing,."" "And the perfect summer retreat Both on and off-screen." "For decades, thousands Of families made mountain lake." "A part of their Summer tradition." "Then in 2002, something Bizarre starting happening." "The lake levels began To drop dramatically." "And by 2008, it had Completely vanished." "No one could explain How it happened." "Evaporation alone could Never account." "For such a dramatic drop." "So the question was, Where did all the water go?" "This, right here, Is the little section of water." "That remains of this lake, The vanishing lake." "It's almost hard to imagine." "That 80 feet over our head." "Was the old surface Of this lake." "This is, like, Basically at the bottom." "Of where the old lake was." "What makes this puzzle Even weirder." "Is that the lake started To come back." "And then stopped filling again." "Today, it's only About 30 percent." "As deep as it was When it was full." "So what on earth Is going on here?" "When this 47-acre Lake dried up in 2008," "Business did, too, and, With it, many local jobs," "Tourism dollars, and countless Family memories yet to be made." "And as employees From the lodge can attest," "It was probably the worst time." "For something Like this to happen." "Not only did our lake go away." "The recession was in, too." "And between the two things, We were devastated." "We didn't know what to do." "It's very depressing to me To see the lake the way it is," "But I'm in hopes That eventually, one day," "I'll see it full again." "No one here is sure Why the lake disappeared." "But if that mystery Could be solved," "Could it lead to a solution To bring mountain lake back?" "To find out, I'm meeting up With a team of specialists." "Who are working To solve the mystery." "Together, we'll deploy An r.O.V. To the bottom." "Of what's left of this lake..." "R.O.V. Is going In the water." "To search for clues About what caused." "A 6,000-year-old lake To suddenly vanish." "Whoa!" "My gosh!" "I'm at mountain lake in virginia." "Trying to solve A perplexing mystery." "What caused this Once-flourishing body of water." "To suddenly disappear?" "And where did All the water go?" "To try to answer These questions," "I'm meeting up With a pair of specialists." "Geophysicist tim bechtel," "Who joined me earlier To investigate duffy's cut," "Is an expert on Underground sensing technology." "And team geologist "Paki" stephenson." "Piloted the initial r.O.V. Inspection of the lake bottom." "Which confirmed Something startling." "Water was leaking out Through four large funnels." "At the bottom." "We set up on A pontoon boat." "Moored just off Where they were spotted." "Somewhere out here Are those old vents." "And what we want to do first." "Is we want to send an r.O.V. Down into the water." "We want to scour the bottom For different areas." "Where the water Might be flowing out." "Paki, here, thinks he has An idea where it is." " You got it, paki?" " I do." "We're ready." "No one has explained fully." "How these vents Could've drained the lake." "Or where the water went." "I searched for other lakes That might offer a clue." "And I came across Oregon's lost lake." "Last winter, it was One and a half times bigger." "Than mountain lake, But by the following summer," "It had disappeared completely." "The reason... multiple openings In the lake bed." "That drain the water Out like plugholes." "But there are Fundamental differences." "Between lost lake And mountain lake." "Lost lake goes through The same cycle every year." "The plugholes are lava tubes Thousands of years old." "That empty into magma chambers Deep underground." "In winter, there's enough rain." "And snowfall to balance The outflow through the tubes." "In summer, it drains dry." "But mountain lake Never fluctuated like this," "At least in recent memory, Before it suddenly disappeared." "Scientists believed it formed Roughly 6,000 years ago." "When a feeder stream Began to collect here." "In a natural pool of water, Forming a lake." "At 3,800 feet above sea level," "Mountain lake Is the highest natural lake." "East of the mississippi." "Most lakes in this region Are much closer to sea level." "So the fact that this lake Even exists here at all." "Is a mystery in itself." "But the locals whose livelihoods Have depended on it for decades." "Were sure glad it did." "That's why when The water disappeared," "The lodge's owners decided." "To seal the holes In the lake bed shut." "In a desperate bid To save the resort." "And they came in here With heavy equipment," "Excavators And, bulldozers." "They dragged down Some of the material." "Off the flanks of the lake." "And filled up Those big funnels." "At first, it seemed like They had found the magic bullet." "And fixed the problem." "Rainfall, underground springs," "And the feeder stream began To refill the lake once again." "Even the fish came back," "Though no one was Stocking the lake." "But as quickly as the solution Seemed to come," "It suddenly stopped working." "And as soon as they pulled Their equipment out," "The lake was rising very fast, Just like that." "And then it stopped." "Everyone was stumped yet again," "As it seemed mountain lake Had a mind of its own." "Could new holes have formed Somewhere else in the lake bed?" "And if so, why?" " Now we set the r.O.V. Up." " We're ready." "The first step to solving This mystery is to check." "If the clay plugs Installed in 2013 held." "Or if water is still Draining through them." "That's where The r.O.V. Comes in." "On the front of the r.O.V., We have a little camera." "We have lights on the side." "Once the r.O.V. Settles," "The bottom of the lake Should become calm and quiet." "But if paki stirs up silt With the thrusters," "And there is a leak, We will see a cloud." "Of fast-moving Sediments streaming into it." "R.O.V. Is going In the water." "That thing can move!" "I like it." "Okay." "We're going down." "Wow." "Can you pan that camera up Just a little bit?" "Paki directs the r.O.V. To the spots that were plugged." "And it looks like all's quiet." "All we see is the light, Fluffy mud just laying." "In a flat plane," "Which tells me There's no leaking." "If any of those funnels Had reopened up," "We wouldn't be seeing this." "So then why isn't The lake filling up?" "Something else has to be Going on down there." "Searching for clues," "Paki pilots our r.O.V. Away from the sealed holes..." "And makes a key discovery." "Right now, I think The mud looks different." "We're finding rocks." "I mean, it looks like you got A boulder field over there." "Lake beds almost Never look like this." "That could be significant." "In fact, it reminds me Of something I saw." "Before I met up With tim and paki." "Walking around the shoreline Right at the moment," "Just trying to get a feel." "For what's going on here In this lake." "As I scouted the shoreline," "I came to a point At the northern end." "Of what is now the lake bed, Close to where the r.O.V. Is." "And something Struck me as unusual." "If you look at this rock..." "I've walked around A lot of places out west." "And the grand canyon." "And you get these kind Of scree fields, right?" "Big boulders that are oblong." "Scree is a collection Of broken rock fragments." "At the base of mountains Or valleys." "That is accumulated Through periodic rock fall." "Caused by landslides Or earthquakes." "And it could be another clue." "About the disappearance Of vanishing lake." "I mean, this does not Look like river rock." "It looks a little bit Like the sides." "Of some of the hills In the grand canyon." "You may not think of virginia As a hotbed of seismic activity." "But believe it or not, it's A pretty active earthquake zone." "In fact, central And southwestern virginia." "Average a magnitude-5 earthquake Or larger every 50 years." "And between 2005 and 2008," "When the lake began To noticeably disappear, 11 minor earthquakes Ranging from 2.0." "To 4.3 magnitude Were recorded in this area." "So could these tremors Be connected, somehow," "To mountain lake's Disappearance?" "Intriguingly, the r.O.V. Is now Revealing that the boulder field" "I saw next to the lake continues." "All the way down To the lake bottom." "That suggests at least part Of this lake was likely affected." "By seismic activity." "So we moved the r.O.V. From the old funnels." "That were repaired." "So we have it kind of up Close to the bank." "Then something new appears On the monitor... whoa." "A fast-moving flow of water." "That looks like it leads To an opening." "That's a huge hole, paki." "This is stunning." "It looks like mountain lake Is still vanishing." "Right before our eyes." "I think we found a place." "Where water is actively Getting sucked out." "But where's the water going?" "And can it be stopped Before it's too late?" "I'm in southwestern virginia." "Investigating what caused." "This once-flourishing mountain Lake to mysteriously vanish." "And our r.O.V. May have Just uncovered a key clue." "I think we found a place." "Where water is actively Getting sucked out." "This discovery opens up A whole host of questions." "What caused this funnel To open up?" "Could it drain the lake Completely dry again?" "And where is all The water going?" "Actually, that looks like It's moving really fast..." "It does." "That is good flow." "I think I can get The sub in there." "Let's follow the water." "Let's see where it goes." "I've yet to figure out What's happened." "To the millions of gallons Of water." "That once filled mountain lake." "But local lore holds A wild theory." "When I was a kid, you know, Before I even started work here," "I'd always heard, you know, There's a lake under this lake." "Like, maybe some giant Underground cavern..." "Exactly." "Right." "Or something that's Basically acting." "As a reservoir Or something." "Exactly." "Could there really be A lake beneath the lake?" "Apparently, according To my research," "There are underground bodies Of water." "Beneath Other seismically active areas." "A massive reservoir Was recently discovered." "Beneath a volcano In the bolivian andes." "And there are signs That similar water pockets lie." "Beneath the volcanic areas." "Of new zealand And washington state." "Could an underground Cavern also exist." "Beneath mountain lake?" "And could that be where All the water is draining to?" "I'm hoping the r.O.V. Can help answer that question." "Look at all the silt Flowing past you." "Wow." "But as it gets closer To the possible source." "Of the leak, It runs into trouble." "I'm stuck." "I can just a wiggle A little bit." "But I can't get out." "Why don't you give A tug on the umbilical?" "See if we get you free." "How far did I go in?" "It's tight." "I don't want to pull on this." "Tugging on the cables could Damage the equipment or worse..." "Detach the cable completely," "Leaving the r.O.V. Stranded below." "So there's only one option..." "To dive in an try to retrieve The r.O.V. By hand." "And while I'm down there," "I can get a close-up Look at the lake bottom." "And scan for clues About where the water is going." "But I'll need to be careful." "We're calling it a cave, But what it really is." "Is nested boulders with Big openings between them." "Sure." "So when you're retrieving The r.O.V.," "Don't move any rocks 'cause We don't want this to settle." "If this were to collapse," "It could just trap Your hand or something." "It's freezing cold, Very cold." "Yeah." "I'm gonna just Swim along the line." "The r.O.V.'s umbilical Leads me toward the trapped sub." "And sure enough, The cable is caught." "I see the r.O.V. Lights." "It's wedged deep in what appears To be a kind of tunnel." "I've been on countless dives In freshwater lakes." "And the topography Of this lake bottom." "Is unlike any I've ever encountered..." "A sprawling pile Of large jagged rocks." "I have to work the sub loose Without dislodging any boulders." "One wrong move could trap The r.O.V. Or me underneath." "After several minutes Of tugging and pulling," "Mission accomplished." "Got it!" "Whoo." "That's a pretty Good-sized hole." "You could lose a lot of water." "In a lake like this over The course of a day." "Or a week or a month." "But I wonder, How much water, exactly?" "Enough to offset the inflow From rainfall and runoff." "And drain the lake dry again?" "I have a way to find out." "I think the next step Is to get some sort." "Of flow meter in there So we can figure out." "How much water's Pumping through." "What we're gonna want you To do is get this positioned." "So the impeller's In the opening." "Okay." "Sounds good." "By measuring the velocity Of the fluid over a known area," "The flow meter can calculate Just how much water." "Is moving through the hole That trapped the r.O.V." "After setting The instrument in place," "It doesn't take long To get a reading." "That's about a million gallons A day leaving this lake." "A million gallons Is more than enough." "To fill an entire Olympic-size swimming pool." "And that's how much water Is leaving this lake every day." "Now, the next question is, Where is it all going?" "That seems like Too much water." "To miss draining out To the surface somewhere." "So could the locals be right?" "Could it be emptying into some Deep subterranean chasm?" "I have a theory." "But to test it..." " you ready, tim?" " Yep." "I'll need to make an earthquake." "I'm in the blue ridge mountains." "Of virginia, investigating Why the lake made famous." "In the classic movie "Dirty dancing"." "Mysteriously disappeared." "And whether it can Be brought back." "I dove to a spot." "Where one-million gallons Of water a day." "Is flowing out through The lake bottom." "Now, I need to figure out Where it's going." "Could it be draining into An underground cavern." "As some locals believe?" "The lake bed around the leak Is very unusual." "It's covered in a field Of jagged boulders." "That could signify A violent seismic past." "The boulder field Continues along the ridge." "To the north of the lake." "And the water seems To be draining." "Toward the north side, too." "So I'm going to follow the trail." "To see if it offers any clues." "About what's going on Under this area." "Near the top of the ridge Is a giant boulder field." "Known to locals As the garden of the gods." "This rock right here." "Looks a lot like what The r.O.V. Got caught in." "The question is, what's going on Beneath this rocky ridge?" "I need a way to peer Deep underground." "So I'm teaming up again With geophysicist tim bechtel." "He has some sophisticated tech." "That will allow us To actually see." "The internal structure Of the ridge." "So we set up A seismic refraction survey." "Seismic refraction gives us A snapshot of the substrate." "By measuring energy pulses That are shot into the ground." "These pulses travel At different speeds." "Depending on the type Of material." "They're passing through." "We'll measure the speed Of these pulses with geophones." "Laid out at precise locations Across the ground." "Imagine putting your ear To the ground." "But like 100,000 times More sensitive." "And this'll allow us to find out." "If the boulders go All the way down," "Or if it's just Hard bedrock." "If the boulder field does extend." "All the way down Beneath the lake bottom," "It could offer an escape path For the water through the ridge." "But if we find only bedrock," "That likely means The water drains straight down." "And the local lore of a lake Under the lake." "Becomes a more distinct Possibility." "Okay." "Shall we?" "Yes." "My job in this experiment Is to create a mini earthquake." "Rob is hitting a steel plate With the sledgehammer." "And we're tracking The seismic waves from that." "You ready, tim?" "Yep!" "We'll need another." "Hit it again." "Okay." "Nice." "How'd it go?" "Looks great." "Hey, rob." "We've got it." "Come back When you're ready." "All right." "As tim crunches the data," "An answer begins to emerge." "This is basically Showing a cross-section." "Of the ridge here." "In the blue field at one end," "The seismic waves reveal Solid quartzite bedrock." "But the green And yellow areas." "Indicate an entirely Different type of material." "In one section of the ridge." "And as we get closer over there To where that boulder field was," "The materials is just Not bedrock at all." "It's more loose And fragmented." "Right." "All of those large boulders." "That we were looking at Over there." "Very likely go all the way To the ground to, what?" "Two hundred feet Down or so." "So the rubble field I saw in my dive." "Wasn't covering holes In the lake bottom." "The rubble field Is the lake bottom." "And it could have dozens Of cracks, crevices," "And holes hidden within it." "That lead all the way through The ridge." "But if that's true, The lake water." "Would be leaking out Somewhere on the other side." "So I head into the woods Downhill of the ridge." "To hunt for signs Of running water." "After and hour of trudging, I'm about a mile from the lake." "And the woods are bone-dry." "I'm starting to think." "Maybe there's something to That local legend after all." "But then..." "Whoa!" "Look at this." "It's water coming out." "Not a whole lot." "Could be ground seepage." "But we can test the water." "If I can trace this water Back to the lake," "That would rule out The underground cavern theory." "And finally solve the mystery of." "Where all that water Is disappearing to." "I grab a sample from the stream." "To compare it To the lake water..." "Stream water right here." "And discover Something intriguing." "The ph levels of the two samples Are a match," "And, more tellingly, So are the tds levels," "Or total dissolved solids," "Which measure the amount Of minerals dissolved in water." "Typically, water emerging From underground." "Would have a higher tds Level than lake water." "Because it has more time To absorb dissolved minerals." "But not here." "That is almost identical to The one we found in the stream." "So this tells me The water from the lake." "Is draining straight Through the ridge." "And into this stream." "Mountain lake is really nothing More than a temporary rest stop." "For runoff heading downhill." "This data, Along with our seismic test." "And underwater exploration," "Also completes the picture." "Of how the lake formed In the first place." "Thousands of years ago, A landslide," "Probably triggered By an earthquake," "Unleashed a bevy of boulders Into this valley," "Creating the ridge That formed the north side." "Of what would Become mountain lake." "As the feeder stream Carried branches and silt." "Through this pile Of rocks, eventually," "They filled in the crevices." "And created a natural dam For water to pool behind." "But that dam and this lake Were never built to last." "It's basically a rubble pile." "That continually is Getting clogged an unclogged." "So that leaves One final question." "Can that natural dam be fixed And mountain lake be saved?" "Well, not exactly." "But it can save itself." "Since my visit, Further research has revealed." "That this process Of filling and draining." "Is actually cyclical." "And these cycles effectively Filter out the sediment." "That builds up on the bottom Through its natural." "Plumbing system under the ridge." "So the lodge has decided." "Not to try to seal the leaks Artificially," "Betting that over time, The lake will heal on its own." "With a little luck," "There still may be generations Of summer memories." "To be made here." "Mountain lake has been hiding Its secrets for centuries." "It just needed science To decode them."