Bridge of the Gods Landslide

[Music] so tonight we're gonna go to one place that's a change for us we usually do a regionals thing but we're going one place and it's called the bridge of the Gods now there's a name isn't that a cool sounding name you've heard of the bridge of the gods where is this thing and the answer is the Columbia River Gorge and you're like well okay but I'm not quite sure where the Columbia River Gorge is well let me help you out this is a map of the Pacific Northwest Idaho and Oregon and Washington and here comes the Columbia River out of the Canadian Rockies here comes the Columbia River crossing the border flowing through the deserts of Eastern Washington here's the Columbia River hanging a right and audaciously heads straight for our biggest mountain range and goes right through it the Columbia River cuts right through with the middle of the Cascade Range going from British Columbia down to northern California now how is that possible how can you take a river and have it go right through a big mountain range put that one on hold we're gonna deal with that in just a bit but the river continues past the mountains it gets to Portland Oregon another hundred miles and it's to the Pacific Ocean okay so where is the Columbia River Gorge it's just this spot right in here where it's a narrow Gorge where the Columbia River is coming right through the middle of the Cascades happen to have a detailed map for you it's almost like I plan this I didn't plan the chalkboard though getting slammed so this is a more detailed map of the Columbia River Gorge and for those that know this place we've got Oregon on one side we got Washington on the other this is the Columbia River coming through the heart of the gorge here the mountains both to the north and to the south there are towns in the south side the Oregon side Hood River Cascade Locks Portland Northside Washington side towns of White Salmon and Stevenson okay so that's where we're going to be tonight and the topic is bridge of the gods so is this a bridge it's like a bridge bridge like I can drive across the bridge of the gods yes you can there is a bridge a bridge right here built in 1926 they obviously chose well this is a place where the Columbia River has choked down to just 300 yards from Washington to Oregon so it's a good place to build a bridge the bridge is still there you can drive a cross you can go down tonight if you want drive across the bridge of the gods bridge it's a toll bridge cost you a buck to cross back and forth as many times as you want if you've got a pocketful of quarters just go nuts down there okay bridge of the gods cantilever bridge I have no idea what that means so this is a geology lecture I'm not going to talk about that bridge so there's something else called the bridge of the gods yes there's a bridge you can drive across but that's not our topic tonight our topic tonight is something called a geologic bridge of the gods okay well I'm not even sure what that means a geologic bridge of the Gods you say where is it well same place all right so I'm listening you say well I guess one way to picture a geologic bridge of the Gods is to imagine some sort of bridge like an actual like Rock Bridge like some sort of arch like like arches national park in southern Utah right oh here's here's that we're looking down the Columbia River Gorge by the way well Oregon's on our left and Washington's on a right the Sun is setting so you're looking west okay you're driving to Portland from here essentially have you ever noticed by the width the gorge is asymmetric that the Washington side has a lower grade e'en than the Oregon side it's steep on the Oregon side okay so are we really kind of picturing this for the bridge of the Gods some sort of rock arch with the Columbia River going underneath no we're not that never existed that's Fantasyland and you say well I thought hold up now I think I saw like a painting or something where they had an actual rock bridge over the Columbia and yes you did there are paintings like that but we get those out of our head those that's not accurate that never happened and you're like well how do you know it never happened well we did this in science right we look for field evidence to reconstruct something that happened long ago and there's no evidence for a rock arch or a rock bridge crossing the Columbia River so what is the bridge of the gods if it's not this actual bridge and by the way wasn't there like a Native American legend where there was a time when you could cross from Oregon into Washington sometime in the past without getting your feet wet yes there is an oral tradition of that and yes that is true there was a time you could cross the Columbia without getting your feet wet well if it's not this rock arch then so what are we talking about it was a landslide the bridge of the gods was a landslide and it's no longer there meaning there was a huge landslide the bridge of the Gods landslide also known as the Bonneville landslide and it was a huge portion of Washington that broke free at some point in the past catastrophic Lee slid down into the valley bottom completely filled the gorge up to 300 feet of loose rubble and dammed the river that was the land bridge quote-unquote that Native Americans were crossing there was this time when this bridge this land bridge this geologic bridge of the gods completely sealed off the valley and so we had not only the land bridge but we had a lake a lake of the Gods that went a hundred and seventy miles up to tri-cities when we dam the river we have a lake up of that landslide damn so that's our topic and you can see in my little map here I've laid out five questions so we've already not if you're if you're a checklist person keeping track you got your pencil out so we know where we're talking now and we just decided that this thing is a landslide and not Iraq arch but there are important questions how is it possible to have how is it possible to have landslides in the Columbia River Gorge is this the only one no there have been hundreds there been hundreds of landslides mostly in the Washington side sliding down and then once we get that out of the way these are the two juicy questions can we say something about when this landslide happened and what have geologists done recently to figure that out do we know the answer and an even more tantalizing question what triggered this thing that's a big landslide blocking the Columbia River come on now so why did it happen there's a conventional answer there's an unconventional answer we're gonna explore both okay so here's the answer for the how this is possible the bedrock layers that happen to be running through the Columbia River Gorge area as you can see in this cartoon are not flat they're tilted they're tilted to the south and the bedrock layers are not tilted to the south all through the Pacific Northwest but in this particular part of the gorge in this part of the map the bedrock layers are tipping to the south tilting to the south and that's important because if you're on the Oregon side what do we have that we can take pictures of waterfalls have you ever noticed that in the Columbia River Gorge the waterfalls are all in the Oregon side they're not on our side that's because of the dipping beds and it's a steep slope because we've got the beds dipping away but those same beds can be found on other words the bedrock layers that's what I'm calling beds can be found on the Washington side and these are basalt lava flows coming from eastern Washington that's lecture that we've already done these are not lavas from the Cascades that's maybe a piece of news you're going right through the Cascade Mountains the Cascades are famous for volcanic eruptions and yet the lavas that you're seeing in the walls of the Columbia Records have nothing to do with the Cascades their lavas that came out of cracks over here in eastern Washington and flowed through the gorge just like the river does okay but the main idea is these landslides keep happening because we have these it's like a deck of cards that's all tilted and ready to go we're sliding these cards essentially and to make matters worse we have sedimentary inter beds between these basalt lava rocks and those beds get real wet some of them are clays Clay's are notorious for being slippery so we've got a recipe for repeated landslides in the bridge of the Gods landslide is just one of many of these events it's a topic tonight because it was relatively recent and impacted many things that we're going to talk about okay that's the house oh my god we're really making progress well I got a lot to say about these last two so we're gonna kind of slow down in our progress but hopefully really dig in now and try to answer the wind and the how excuse me the wind and the why okay so there we go I think we should talk about this landslide and make sure that we are realized that that thing actually happened I think I want to do that first and then I'm going to do some more drawing so how are we sure that this landslide really did happen well we've had landslides for hundreds and hundreds of years and people have been observing these and as geologists we know what it looks like after a landslide happens what do you look for well you look for a big pile of rubble this isn't rocket science now okay big blocks of rock and smaller rocks that are in this big jumbled mess and this whole area here then is this jumbled mess of material that's the true landslide itself the bridge of the Gods land five material remember now in a bit we're going to realize that this was originally all the way across to Oregon it completely sealed off the the gorge but since that time the Columbia River has reestablish yourself that's why we even need the bridge to get across okay fine but we're looking for evidence to convince ourselves that it really was a landslide that's one thing in this material we have links lakes down in the in the middle of a river valley that that shouldn't be river valleys are rivers that are draining we're getting the water out of there but we've got these lakes sitting in the middle of this area of this middle of this map that tells us that a landslide happened landslides screw up drainages when we have precipitation on the on the landslides there's nowhere for the water to go we create these sag ponds for these lakes there's something called Table Mountain which presides above the bridge of the Gods landslide Table Mountain is where the mountain broke and so I head scarp for the landslide a place where the actual Mountain split and you can look right into the guts of the mountain and it's a sheer cliff with a bunch of exposed rock layers that's there to look at and even what if you're still doubting that the landslide happened okay upstream of the landslide are thousands of trees that are dead they're standing but they're dead and those trees were killed because when we dammed the river we formed this lake the lake completely submerged they drown these trees and since we got rid of the lake we go back to the river and we can see some of these standing dead trees Lewis and Clark were the first guys to really describe these and put them into journals okay there's a lot of evidence that we had a landslide and not this rock arch but you came to this title to talk of it you came to this talk the title is the bridge of the Gods landslide so I'm like you know you already knew all that okay let's move on I need to draw now I want to keep this visible but I need to draw a little bit about this lake because that's obviously an interesting part of this discussion I did my best to email experts with not only the lake but with fish people I don't know anything about fish but if we're blocking the Columbia River and we're trying to get these salmon to do their normal thing and come up the river there's some issues there right so I managed make some contact with the guy named Jerry Smith who's a fish paleontologist and he helped me with some ideas and the geologists were gonna deal with is Jim O'Connor who was really the specialist in Columbia River Gorge geology and his current project one of his current projects is to work out some details on this Lake of the Gods okay gosh you know what am I gonna do here I'm gonna I'm gonna try to use both of these camera people I hope you can kind of play along here I want to use that one in this one all right so let's do this let's let's screw with this map let's actually have the landslide the landslide just happened okay so we've got the landslide completely blocking the gorge and we're going to back up this river to the point where we have this link and again the lake is going all the way up to tri-cities on in seventy miles of valley I'd like to do a cross-section of the same thing so this is a map of the Bonneville of the Bonneville Landsat otherwise known as the bridge of the gods landslide this is a cross-section of the same thing I better write down this is a cross-section let's put a Native American up here okay so the before the landslide happened we had the Columbia River flowing from east to west okay do you see what we're doing we're looking down on the landslide here we're now looking at the same landslide from the side and this is a 300 foot tall landslide that just came down into the valley we all got we all good now okay so a Jim O'Connor has been doing some work to try to figure out how long would it take to fill this bathtub behind the landslide dam before it breaches the landslide before it actually started the water starts to spill over the top of this thing and so o'connor has taken the average flow velocity of the Columbia historically he's worked with details of the morphology of the basin that we're talking about he's a numbers guy and a fluid hydraulics guy and so we're just gonna have to take his work and I got to go to some notes now so he has good evidence now Jim O'Connor does that the Lake of the Gods so let's label this this is the bridge of the gods Bo TG this is the lake of the gods so at maximum depth the lake of the Gods was 300 feet deep this water behind this barrier and O'Connor did some work to try to figure out how long does it take to fill this bathtub essentially behind this landslide dam his basic answer is about six months based on the rate of the water and the size of the basement we need to fill six months to raise this thing until if we go six months after we don't even we don't know when this thing happened yet by the way right this could be a thousand years ago a million years ago last Tuesday just kidding so we don't know we don't know when but we're just working out the timing of this whenever this happened it happened quickly it dammed the river six months to fill the Lake of the Gods up to three hundred feet elevation so now water is going to start dribbling over the top of this dam this landslide dam now how are the salmon dealing with this probably not well they're probably spawning still just here they can't get any further up the river than this and they want to get up the Yakama they want to get up the snake and all the rest of our beloved rivers here in Eastern Washington but then it gets a little murky when does the rivers start working down through this dam another when can we start restoring this river before I try to get a few dates on that the concept we want is let me try this before the landslide we can imagine the river channel let's just for simplicity say coming right down the middle of the floodplain okay so there's a floodplain on both sides we've got trees growing on the floodplain they're not in the river they're next to the river and it's a nice happy idyllic scene fine now we bring the landslide in of course we're going to stop this we're going to have that River go away we're going to make the Lake of the Gods and my point here on this map is that when we finally get the Columbia to start flowing again it's not going to be able to be in its familiar course it's going to find a way to kind of circle around the toe of the landslide so the channel itself shifted about a mile to the south to get to navigate this bridge of the Gods landslide and really it's still trying to get through the landslide in other words it has down quite quite a bit but there are still tremendous Rapids that Lewis and Clark had to deal with big rocks in the river those big rocks are there because the river is trying to get through this at this bridge of the gods Lancelot okay good so we're a little bit away from the original course of that River O'Connor's got a lot of work but here's the couple things I want to try to bring along to you so if this is our our high-water mark of 300 feet Lake of the Gods O'Connor has good evidence that for a while it could be months could be years maybe even more that the lake level was lowered just 260 feet so there was a 40-foot drop meaning that there was some sort of breaching a partial breach of the landslide dam to get the lake to this level and you're like well how does he know that originally the lake was up here and then the lake went down to 260 well he's got some river deltas coming in from side channels that are at that particular elevation and those river deltas are substantial and so he's got a good datum here that he thinks that that Lake was at this elevation for a while so his one of his emails to me was helping me see that this is about a 5-mile distance and these are Rapids now at this time when the lake is at 260 elevation we've got incredible hellacious set of Rapids that have to rise 260 feet in a 5-mile stretch what would what did that look like that the Columbia is now flowing but it's going through a major section of the landslide dam Jerry Smith is unsure or maybe I didn't ask the question correctly but can the salmon deal with that a 260 foot climb over a 5-mile span back at this time Jerry's general comments are look we've got salmon that are not going extinct we've got a million or two million years of generation of these salmon they've dealt with hundreds of these landslides this is not a do or die situation we don't have salmon going extinct because of this particular event so you maybe want more you want actual numbers you know how long did it take for the river to go through O'Connor says we can't do that we don't have the data yet maybe we'll never have the data to really figure out exactly where we had the bridge but we can say this there was not one catastrophic breach of this landslide dam in other words there wasn't one event to just cut through the whole thing from O'Connor's work that is not true we have instead kind of periodic or episodic breaches of this dam probably for some freshwater floods every once in a while well he does have however is one outburst flood so instead of a gradual breaching of this dam there was one significant out purge flood how does he know he's got boulders and then sand at Portland and then silt further downstream of Portland that all work in one particular timeframe and he has Mount st. Helens ash from 1480 ad sitting on top of that out first deposit let me say that again for the first time we're actually talking about a time now this is a date not that long ago this isn't thousands of years ago this isn't millions of years ago this is 14 80 AD a Mont st. Helens ash sitting on top of an outburst flood deposit that indicates one significant breach event of the bridge of the gods landslide so what can we say we can say the landslide happened sometime before 1480 based on the fact we have an outburst event where we have parts of the dam that are now downstream more coming on the dates but that's our first little taste of that okay you're doing all right I'm going to keep rolling whether you are enough that's not very nice to me is it no I'm gonna keep that there so let me check my notes right right oh the downed trees or the drowned trees I should say let's put some trees in here so remember our trees they are here they got completely soaked more than silk there they're completely underwater in this bathtub water can we figure out when those trees died if we can figure out the age of death of the trees we can get an age for the landslides well there's a guy named Donald Lawrence that was in here back in the 1930s they were about to put the Bonneville Dam in Bonneville Dam is here in 1938 they open today they opened a Bonneville Dam so before the Bonneville Dam was actually put in this guy was running around trying to survey all these trees he visited more than a thousand of these dead trees and cataloged them and did some tree ring analysis and tried to ultimately come up with the age of the Bonneville landslide or the bridge of the god last slide same thing so that didn't work so well he didn't get down to an actual date but many of those sample he collected have been radiocarbon dated more recently and so I'll cut to the chase from dating the trees from dating the trees we now can get down to here's our best bracket for the age of the bridge of the Gods landslide the landslide happened quickly it happened quickly didn't happen during this whole span but using the age of the trees and the tree ring analysis and the deposit downstream this is as close as we can get the bridge of the Gods landslide happens sometime during this two-and-a-half decades span okay so checklist people there we go we've got a date for this event now can we then do one more thing on the chalkboard can we actually speculate on why that event happened I've got other facts and figures here I'm just going to blow by alright good so I think we need a timeline before we do anything else so give me a chance here kind of warm in the room tonight for reasons I don't understand maybe it's cuz it's damn near spring outside that's maybe part of it spring break is common we're done with the winter quarter feels great March Madness oh man what a great time of the year so let me do this if you if you give me a chance just give me a chance that's all I ask just give me a chance so these are dates ad 1400 AD 1500 AD we got too much to juggle in our minds now I think we need some something to keep track of these dates okay let's put some things in here so what did we just decide we decided that the bridge of the Gods landslide happened 1425 to 1450 do you see my timeline here Lewis and Clark came through and took notes in 1805 late October of 1805 they noticed these dead trees they noticed the landslide they deduced there was a landslide but looking at the trees in particular they thought well in their journals they thought well this thing probably happened just a couple decades before us Lewis and Clark did they said with big landslide happened and probably happened in the late 1700s we now know that that's not true ok fine they did great work obviously the fellow Laura started looking at trees that are living on top of the Bonneville landslides or the bridge of the Gods landslides and the oldest tree he was able to find dated to 1562 which tree is that that's the oldest living tree on top of the landslide to help us realize that the landslide happened had to happen before that fine what else can we put on our timeline well 1492 Columbus sailed the ocean blue the birth of the USA 1776 what could do some other things but we don't need to here's where I'm headed you've heard that we have great earthquakes haven't you magnitude 9 earthquake this was not known until the 1980s Brian had water figured it out when's the last time we had a great earthquake that's right the Year 1700 magnitude 9 a great earthquake you see where I'm going with this and before I go much further I got to choose my words really carefully are you ready there is a chance there is a chance that there's a connection between great earthquakes magnitude 9 earthquake that have shook the entire Pacific Northwest and big landslides like this I am NOT tonight saying overwhelming evidence to tie those two things together but there's a chance because of the evidence I'm about to share with you okay are we clear on that not peddling one thing not in love with it but boy you can't ignore the evidence I'm about to share with you to put that together and you're like what you just showed us that the big earthquake was 1700 and you just said that we have this event that happened centuries earlier hello friends okay we're getting the phone we got the phone good it's all right we have a cycle of great earthquakes they happen every so often they didn't happen just once and tonight we're gonna look at evidence for a second two most recent great earthquake guess when it happened so I got an email from a guy named David in Portland and he sent a nice email and asked me a question do you think the bridge of the Gods was triggered by a full rip a magnitude 9 earthquake and I emailed back and I said I'm sorry to have it know we've got this date for the bridge of the gods and we've got this date for the great earthquake so we thought that for a while but we don't think that anymore sorry thanks for the email and he David from Portland emailed right back and said I wasn't talking about the 1700 full rep I just saw something in the Portland newspaper and they had data for many of the full reps and they had specific dates for these great earthquakes and the second two most recent full rip was 14 68 plus or minus 50 there's always error with these events so I'm like wow I'd never seen that specific date before is that really true he said well that's what I read in that maybe they had a little date table and they had all this stuff so I started emailing the first guy that I emailed was a guy named Chris Goldfinger that's a name and Chris Goldfinger is a specialist in studying deposits out in the ocean floor and you're like well why is he out there well when we have a great earthquake there are underwater landslides that send deposits down slopes and the nest are the result of those underwater landslides is something called a turbidite on turbidite what's a turbidite it's an underwater landslide deposit and Chris Goldfinger has studied at the mouth of each of these submarine canyons these are Grand Canyon like canyons by the way underwater okay I told you we were just going one place huh okay I'm sorry we're out in the ocean now just for a second okay so Goldfinger has been studying these turbidite deposits offshore and he's got a 1700 at the Year 1700 great earthquake turbine died in every one of these places so that confirms that we had this great earthquake and the ground shook and these underwater landslides came down all these canyons at the same time but in most of these locations he's got another turbidite he calls it t2 turbidite - not t1 but ii ii ii to youngest full rim and when I emailed him I said this guy saw this thing in The Oregonian where's this date coming from so that's that's my stuff those are my dates but we actually have a better date now a more accurate date instead of 1468 like it was in the newspaper our better date with a couple new techniques is 1456 plus or minus 50 and so I'm saying well that's amazing I said do you think there's a connection at all and he's like well I don't know but what do they have for the newest dates on the bridge of the Gods landslide and I said pretty much the same thing 1425 to 1450 so that's kind of where we are a potential connection and the plot thickens a little bit with the visuals I'm going to have for you in just a couple of seconds and we're going to visit with Chris Goldfinger and Brian Atwater and Jim O'Connor and a bunch of others so be patient for that we'll go to the screen in just a second well let's go through this whole stuff again but real we need the visuals it's such a beautiful place and we'll go through some of these same questions and add quite a bit of content so it's not the same content over and over again you are sitting here in beautiful Ellensburg Washington we want to head down to the Columbia River Gorge don't we it takes us three and a half hours to get to Portland through the gorge and this is the place my goodness sakes there's so much to absorb as you approach from the East Mount Hood presiding on the Oregon side love is on the Washington side and this was the scene more than a century ago same idea beautiful beautiful beautiful the lava layers have nothing to do with the Cascades we made that point quickly there's railroads on both sides of the river there's all sorts of transportation on both sides of the river and when we finally get in the middle of the Columbia River Gorge we've got our destination for tonight the bridge of the gods landslide just ups river of the Bonneville Dam so a map from Davy Barnwell to help us on the worgen side The Dalles rowena crest Moser Hood River here's the bridge of the Gods the actual bridge we eventually get to Portland you know where we are Google Maps helped us the best western plus right there by the bridge and BEST WESTERN PLUS where I stay when I go down there and the bridge of bridge side restaurant right next door and both of those places are right at the foot of this bridge there it is built in 1926 they had a big crowd for the grand opening Charles berg is showing up in his airplane flying from portland he barnstormed for the crowd he goes over the bridge he does a 180 he comes under the bridge on the way back to portland crowd goes wild so we're going to go onto the bridge with this person i don't have his name but I found this on youtube thank you my UAV fits person did a nice job with his drone flying underneath the bridge of the gods so I found some footage also on YouTube of the construction of this bridge back in the 20s it was a different time there's a little boat down there for safety [Laughter] some sizzling hot rivets that they're tossing up to the guy as the riveting the bridge together kind of hard to believe this is less than a hundred years ago and this was these were the working conditions for these guys but they knew what they were doing obviously and according to their sources that were able to find nobody fell in nobody had a problem truly amazing the bridge of the gods all right well the bridge still stands those guys did a hell of a job still they're doing a nice job and you can drive back and forth this is that toll bridge for a dollar and you might know this bridge for other reasons this is the place to cross the Columbia River if you're hiking from Mexico to Canada on the Pacific Crest Trail can walk right across the bridge in fact here's a gal who has put some videos of her journey on the Pacific Crest Trail on YouTube Gillian Larson and she's riding a horse on the Pacific Crest Trail she's down here in California and the Mojave and working her way north trying to get eventually to Canada on this Pacific Crest Trail and here she is after going through all of California and all of Oregon and she's dropping down to the bridge and her mother is taking the video now in the vehicle behind her Pacific Crest Trail emblem and here's Gillian are ready to pay her dollar and the woman gives it right back that's very much okay great so that's the bridge but that's not our topic right that's not our topic oh this must be the topic oh my goodness sakes where did I find this in the lobby of the BEST WESTERN PLUS hotel [Laughter] right behind the front desk so we might as well do this what the hell we're at it no evidence for a rock bridge over the Columbia instead we want this now check it out check this out for a second so here's the bridge that Gillian was just crossing out on her horse four miles downriver here's the Bonneville Dam in three places they put the dam in there in 1938 because again of the narrowness of the channel look at these lakes in the middle of the river everything in brown of course is the landslide the bridge of the Gods landslide that originally sealed off the valley and the river has restored itself so shots from Tom Foster huge floods calm the bridge of the Gods the actual bridge the Bonneville Dam this is all material that slid south from Washington this is the landslide itself you'll see it the next time you drive if you haven't noticed it before Bonneville Dam built in this landslide complex bridge of the Gods the bridge dotted trails the Pacific Crest Trail Bonneville Dam you got it now right Beacon Rock is downriver Skamania Lodge is close by on the Washington side Chris marked the Silver Fox with his red hair we'll talk about him in a second I guess we can talk about him now we filmed a video program a little five-minute TV program on this bridge of the Gods landslide and we needed permission so a ranger is supervising our filming at Bonneville Dam and let's move on now I'm 55 years old and I'm not kidding you that it dawned on me just a few months ago what a ka actually stands for I have no idea also known as Wow okay great the light bulb went on Bridge of the gods Bonneville landslide same thing I'm using them interchangeably tonight and they should be used interchangeably more shots aerial shots of the Bonneville landslides bridge of the gods lens land can you see it now I don't know if you were doubting at all but hopefully it should be super obvious to you no more imagery for you here's the bridge bridge here's our landslide that broke free from Table Mountain so before we look carefully at the landslide itself let's remind ourselves that these major lava flows these are beautiful photos from huge floods calm these mutant huge lava flows are coming from the east they're coming from the east here's advantage Washington in these monster lava flows so again beautiful photograph Mount Hood basalt no connection between the two zero instead those basalt flows are the flood basalts of Eastern Washington that predate everything in this lecture we're back 15 million years ago now and here's a couple quick maps to show you how much of the Pacific Northwest was buried in basalt lava and where did that lava come from it came from these cracks again our topic tonight is right in here so again there's a regional story with the rock layers that you see exposed and in fact the rock layers that are failing to create the bridge of the gods landslides so this is the scene in eastern Washington 15 million years ago when those lavas were coming to the surface and today if we zoom in and look carefully there's specific events this is a lava flow that came out 15 point 4 million years ago and flowed through the Cascades the Cascades that were lower at that time and noticed there's a finger of this lava flow that crosses over the mountains and gets to yaquina head and another finger of this follows the Columbia the whole way so there's debate from for some that that perhaps there was quite a bit of crossing of the Columbia of basalt lavas and the Cascades the Cascades about lifted quite a bit since more coming on that in just a second this is Rowena Dell man it's a great time of the year to be down there this spring hope you go down and enjoy it this way doing the chalkboard this is from Marlene Miller's roadsides geology book of Oregon Washington and the Wright South Oregon and our dipping beds are dipping beds right for slope failure and so the waterfalls are on the Oregon side because of what we talked about and see those you can maybe notice these tilted beds as you drive up and down the gorge why are those beds tilted I'm saying they're tilted but can we investigate briefly why they're tilted so the original flat lane basalt layers were squeezed and compressed and warped and those warps are not only in the gorge but they're all the way up here to Yakima and Ellensburg here's a little short video clip to help us see that and this land has been lifting against the river we know the river is older because of its curvy nature meanders only form when an area is flat so you got it the river was here first when you air was flat then this land started to the lift and these ridges started to grow why okay so I'm much longer after the chalkboard session and finally answering that first question I had for you how is it possible for the Columbia River to cut through the Cascades the answer is the rivers been there a lot longer than the Cascades have it's not that we had a powerful River it's that the river has an old age and the uplift of the Cascades as well as these local ridges is the response here's a good shot of that the Columbia River at The Dalles hangs a right goes right through a major Ridge the Columbia Hills and that's because the Columbia Hills anticline as younger than the river itself more shot showing the same thing from Marly Miller so familiarly seen to all of us the scenery is great but maybe some new ideas for you so those tilted layers are related to the Yakima folds as my point the ridges we have south of Ellensburg are also the reason that these ridges and these beds are tilting so much now again why are we getting the tilting there's a GPS Network operated by the guys in my department up on the third floor they're very bright people and they have these instruments across the northwest that are communicating with our building on the top floor of the new science 2 building it's called the panga network and these instruments are helping us understand tiny movements in the crust tiny movements in the crust and those that data comes in every half a second from all those stations to the third floor of science 2 and if you have every one of those red dots be one of these little stations there's an interesting thing to point out here's a little thumbnail sketch of every one of those instruments in this network so we have hardworking people in our department who monitor and maintain those instruments here are the vectors showing the motion of every one of those stations and can you see can you see that California Oregon and Washington are doing a graceful clockwise rotation that's the answer for why these beds are tilted they're tilted because northern Washington and Canada is not rotating but everybody else is and so we're squeezing the layers and tilting them as a result so if it wasn't for these clockwise rotation diagrams we wouldn't have the Bonneville landslide we wouldn't have the bridge of the Gods landslide we need those tilted beds to do that and the tilting is coming from this tectonic story I also didn't mention in the chalkboard discussion that there is an impact of these things called the ice age floods most of you know the general story here's something in case you don't this is the last two million years of time ice water is coming from the Pacific Northwest crossing the Pacific Northwest getting into the Columbia River Gorge and eventually coming all the way down to the Pacific Ocean here's a place in eastern Washington called Dry Falls and this is one of our simulations to show how dramatic those floods were and one question is well what happened to the water where did it go it all came down the Columbia River Gorge it all came right through our stopping our topic tonight our study site so there is an ice age floods impact but we don't want to be too carried away with the ice age floods the ice age floods did not create the Columbia Gorge the ice age floods did not do tremendous amounts of erosion in the Columbia River Gorge it cleaned it out it took some of those landslides out of there this is long before the bridge of the gods by the way but I'm just pointing out that when you drive the Columbia River Gorge you can see the bottom two-thirds of the walls are heavily scoured and you can see the basalt rock layers but the upper third you can't see them that's because they flood the Missoula floods were not that high bottom part scoured upper part of the gorge not scoured by water this is Beacon Rock downstream of bridge of the gods totally under water during the major Ice Age flood events this is the vista house looking east here's Beacon Rock and the bridge of the Gods is in the distance during the biggest Ice Age floods the flood water was almost up to the parking lot of the Vista house but again not a major player in forming the gorge and certainly not a player in our landslide topic tonight so why low Falls is upstream of the bridge of the Gods landslides and it was an ice age floods feature those Rapids were not the result of a landslide but result of Ice Age floods digging and scouring and and excavating rock and this is upriver of The Dalles so where we had Celilo Falls we now have quiet water behind one of the dams so let's get into the juicy part and talk about the details here's the old shoreline of the Lake of the Gods in blue behind the Bonneville landslide which completely sealed off the gorge can we see where the mountain split we sure can the headscarf of Table Mountain helps us do that that's how this help us out that's Table Mountain right there you can see where that Mountain split broke and slid down to dam the Columbia River the bridge of the gods this is Cascade Locks Oregon at the heart of the gorge where the river passes through the center of the Cascade Mountains majestic waterfalls plunge down the steep walls of the Oregon side of the river with the historic Columbia River Highway winding its way through dense forests the river is choked down here it's nowhere near this narrow anywhere else in the gorge why good question we know the answer and instead of just Table Mountain breaking free there are other headscarves with other landslides with other days so the point is our landslide tonight is one of many landslides that have happened on the Washington side of the river presumably many of those landslides the salmon had to deal with as well Lewis and Clark 1805 as Lewis and Clark approached this part of the gorge in 1805 Clark noted thousands of fresh-looking partially submerged trees in the Columbia River a submerged forest with trees up to 25 feet tall and Lewis and Clark were about to encounter a set of rocky rabbits the great chute they call the Cascades of the Columbia represented here by artist Charles Fritts swift perilous Rapids navigated by the Corps of Discovery in wooden boats but where did this rocky pinch point in the river come from ok so old photographs after Lewis and Clark of course in 1805 but before the dams were put in in 1930s and 40s here's the old rapids that the Lewis and Clark had to deal with even as recently as 1932 was a serious place and it was a serious place because of those big blocks as big boulders that are part of the bridge of the Gods landslide so you can see what I mean the Columbia River has not completed its job of completely getting through all the rest of that landslide material but obviously it's restored itself and the salmon are grateful for that back in the 1840s the first visual confirmation that those dead trees were there in the middle of the river upstream of the Bonneville Dam the Bonneville landslide so these were a curiosity for many years and then geologists started studying them very carefully and trying to work with this specific story most thought of landslides was responsible not everybody did and this is Don Lawrence the guy who spent many summers in the 30s before the dams were put in two categorized catalogue and study and sample thousand more than a thousand of these pine trees and other kinds of trees that were killed why are these trees dead they were completely under the Lake of the Gods remember when you do find a buried tree with the bark on it and if the tree has a lot of annual growth rings in it well that is an opportunity to use a good technique called wiggle match radiocarbon dating with this wiggling decay curve from radiocarbon and the computer software helps you match it up to the best possible fit and that really allows you to get within a decade or two of the actual date of the event the actual calendar date sometimes so that's Pat Pringle the fellow who's been able to get our radiocarbon years down to that window that we had along with the work of Jim O'Connor so we're back to Chris smart from central coming down last summer and visiting with the Maine geologist that were profiling tonight Jim O'Connor portland-based USGS geologist hell of a nice guy and spent the morning with us right there by the BEST WESTERN chris getting his camera set up and we got Jim on camera talking about his work with the lake of the gods and the breaching of the landslide geologist Jim O'Connor and colleagues continue to zero in on the exact date at the Bonneville landslide the bridge of the gods we're still working out the whole sequence of events here but what we know or think we know so far is that this landslide occurred sometime between 1425 and 1450 ad a lake formed behind the landslide dam the land site completely blocked the Columbia River the lake was maybe close to 300 feet deep it spilled over but at some point it breached the landslide dam and it breached catastrophic Lee sending a huge flood down the Columbia all the way to the Pacific and recently discovered sediment on the seafloor suggest there may have been a large earthquake in the mid 1400s could that have been the trigger for the bridge of the Gods landslide [Music] today the Rapids as well as most of the Cascades locks and canal are underwater drowned in 1938 by the reservoir behind Bonneville bata the bridge of the Gods was here almost 600 years ago but how many more landslides were here in the last couple of million years and when will the next big landslide happen fine work by Chris smart from Central Washington University okay we're finishing up with our discussion of a potential a potential a potential connection between seismic activity and this big landslide Lewis and Clark thought the landslide happened a couple of decades before their journey O'Connor and Pringle now have the date between 1425 and 1450 if we go offshore we go to the submarine canyons and we realize we have these history of great earthquakes in the Pacific Northwest we can hoe it all to this fella here Brian Atwater who put this story together he's the guy that documented that we had a great earthquake the night of January 26th 1700 at 9 o'clock local time and if you're not sure how he came up with that we've had a lecture on that before check it out so here's that water and every one of these yellow circles finding evidence for great earthquakes not just in 1700 but before then here's the tectonic model that we have the plate tectonic model that we have for these great earthquakes we subduction plate every few hundred years we build up enough energy along the boundary between the subducting plate than the overriding plate to finally fail the boundary release the energy displace the water create terrifying tsunami and shake the ground like hell rinse and repeat I'm afraid so here's another animation showing the same thing sorry let's go back here's another animation showing the same thing we're subducting the Juan de Fuca plate all along the coastline from Vancouver Island down to Northern California and this is the 1,700 of em were the entire margin ruptures so it's a Pacific Northwest story and we're not saying tonight that that event in 1700 has anything to do with the bridge of the Gods landslide why because the dates are wrong right but what we are saying is that there's a potential story with the second two most recent great earthquake hears that water and how we find some of the coastal evidence Atwater believes he has found proof of a whole series of tsunamis stretching back 5,000 years each layer of sand in this sample represents a separate tsunami their places at Cascadia where I've seen nine stacked up in a column about 20 feet long nine buried soil some of them coated with little sand sheets and and you know you you think okay it's not a question of if but it's just a matter of Wham so Brian is a famous geologist and he's famous because of that work among other things but he's the specialist on the coast on the Washington and Oregon coast he knows how to read this mud and how to find these horizons that tell us of great earthquakes so here's the 1700s now this is Brian out water at the coast right so he doesn't have anything from 1425 to 1450 so let's slow our roll here just a second Goldfinger's the guy that's got the turbidite that's coming but on the coast here there is no evidence of a great earthquake from our time of the bridge of the Gods landslide so maybe we need to pause but we do have one two three four five significant events and if you're trying to picture what one of these earthquakes was like I'm afraid we've had a couple of them in the last decade and a half and if you're old enough to remember Alaska and Chile back in the 60s those were all great earthquakes all great earthquakes and every time you have a great earthquake you're in a subduction zone that's unlocking its energy this is the one that happened the day after Christmas 2004 and we send a tsunami across the Indian Ocean we all remember Tohoku in Japan and more recently look at the death toll here from that earthquake and tsunami I mean wow this is Chris Goldfinger the guy we've been talking about he happened to be in Japan during this 2011 great earthquake so he's being interviewed by Nova to describe the tsunami experience once the wave starts to pick up part of a town the warehouses along the dock the debris and all that then it becomes more like a glacier you know it's it's a moving wall of debris and the more mass it has the more power it has as it comes in it doesn't really look like water beyond some point it looks like the entire town is flowing in and and it is so all the mass of all the buildings cars refrigerators and everything that's in that wall it's essentially a debris glacier at that point and it just keeps coming in okay we don't need any more of that so it seems like we're on a tangent but we're not remember what we're doing we're trying to talk about a potential trigger for the bridge of the Gods landslides and we're almost there with Chris Goldfinger's turbidite so let's get to these emails so I mentioned to you last fall I get an email from David in Portland I've never met him a mature guy happened to find one of my videos on YouTube and said do I think the bridge of the Gods landslide was triggered by the sixth 1468 ad great earthquake and again my first thought is I looked up this and I'm like well there isn't one then from Atwater's evidence this is what David saw in the Portland newspaper a plot of the last 10,000 years of time here are the earthquakes along the pacific northwest coast of magnitude 9 a full rip eight and a half eight magnitude 7 etc and David's I was drawn to what we're talking about the second most recent full rip in other words the entire length of the Cascadia subduction zone releases energy estimated at eight point seven instead of nine four magnitude and that article also had a little plot of all the years and the length of the ruptures and whether it was a partial or a full rip offshore so that prompted me to go okay I guess this is really something this is from Sandy Downes books and there have been 20 of these full rip 9.0 in the last 10,000 years and another 20 partial according to the evidence that Chris Goldfinger has let me remind you now and add some visuals here we are offshore we have a big earthquake presumably we shake the ground dramatically we send an underwater landslide called a turbidity current down the channel and that underwater landslide finally comes to rest this is a landslide through water not a landslide through air so we are going to get some sorting this is a graded bed as opposed to the bridge of the Gods landslide which is just a jumbled poorly sorted mess so I emailed Chris in fact I emailed him on a Saturday morning at breakfast time sent the email went out and mowed the lawn got back there's a full email from Chris Goldfinger Saturday morning this guy's working all the time so he had a full email and basically said yeah that tables my stuff compiled something else we've got a better date 1456 plus or minus 50 and our turbidite 2 is clearly present along the full length of Cascadia in dozens of course it exists well then I couldn't hold it I got had to email Brian out a lotta the guy from the coast and I said here's what I'm hearing about this t2 what do you think remember now this is that water from the coast that water had a completely different explanation or possible interpretation for that thing we're calling t2 Brian says how about that's a deposit offshore that's from breaching the landslide remember we had that deposit coming down the Columbia River that Al Connor had with the Mount st. Helens ash on top of it maybe you flush a bunch of that sediment out offshore and maybe that's a current a high-density current that's flowing at the base of the ocean and maybe instead of a great earthquake 42 maybe it's the actual breaching of the landslide emailed O'Connor I was on a roll this is all on Saturday by the way all these guys are working on Saturday it's impressive and O'Connor says he can't really comment on the teeth to turbidite thing but he does have that partial failure of the landslide dam and we can follow that all the way down to the lower estuary of the Columbia went back to Goldfinger one more time I suppose would be on Saturday by now he says man we got this t 2 at most of these underwater canyons we've even got the T 2 in a basin that isn't connected to the sediment coming from North America and so he's still wondering if there's a there's an earthquake connection so to review from the work of Pringle and O'Connor we've got the landslides between 1425 and 1450 do we have a for-sure trigger for that landslide we do not but we've got a sediment layer for sure from the age that matches with this bridge of the god landslides there's a difference of opinion currently at least by email on how to interpret that sediment horizon so that's the bridge of the gods we've answered our questions tilted beds for sure the conventional answer was just a wet series of years and we just had a landslide because things were soaked we can add the quake story if we're feeling gutsy roadside geology of Oregon is a wonderful new book by Marlene Miller she's got a also a brand new book called roadside geology of Washington I encourage you to check those out if you're interested in the huge flood story huge floods calm by Tom Foster and Pasco there's an excellent resource for free and before we quit since is the last of our four winter lectures I want to just point out that I want to thank the University that I worked for for encouraging these kinds of outreach efforts and this you paid for this brand-new building that we have on the campus of Central Washington University I want to remind you that I opened my class to the public so we always have some folks coming in and sitting in with these college kids and a special shout out to Bob and Tony who worked the grounds the campus I said hey if you guys ever find any more of these old chalkboards I want some and they found these two in the basement of Shaw Schmeiser building a few years ago and those are the bills chalkboards have been using the last couple elections thanks very much everybody [Applause]

Channel: Central Washington University

Views: 205,590

Rating: 4.8904252 out of 5

Keywords: Bridge of the Gods, Bonneville Landslide, Bonneville Dam, Cascade Locks, Nick Zentner, Columbia River Gorge, Brian Atwater, Chris Goldfinger

Id: FVZYzHGvDX4

Length: 65min 22sec (3922 seconds)

Published: Wed Apr 04 2018