Lake Chelan Geology

[Music] all right well lake chelan geology right you came to listen to a lecture on lakeshore land geology let's start by saying this let's say you've got a friend on the east coast his name is jerry and jerry calls you out of the blue and he says hey good news i'm going to come visit you in washington i've been hearing you talk about all this geology out in washington i want to see it firsthand and you're like okay jerry sounds good he says i know you've got a lot of different kinds of geology out there right yes we do jerry he says great i'll be there on a tuesday and you're like you'll be here on a tuesday he's like yeah i'm going to come for one day i want to see as much geology as i can in one day where would you take jerry where would you take jerry from new jersey rainier dry falls west coast of washington you'd have a theme or two but you wouldn't have the whole smorgasbord that you need to give jerry i think i would take jerry to lake chelan does that surprise you there's more up there than a lake here's a laundry list of all the wonderful geology in the lake chelan area canada ice sheet alpine glaciers third deepest lake in the united states the columbia river glacial lake chelan ice age floods flood basalts exotic terrains metamorphic rocks granite batholiths and oh by the way the biggest earthquake since the civil war in washington we're going to cram all that into tonight's lecture and i want to do it in three parts yeah we're going to start with the lake and how the lake formed that's probably why you came but i want to do more than that after that we'll do a little bit on the bedrock there's beautiful bedrock up there visually beautiful and i want to talk about that earthquake as well and then we'll look at the visuals and go through the same three guys again you ready you are okay let's do it where is this lake ellensburg is here that's you the hell home center tonight right on this beautiful winter night we're going up here it's a lake lake chelan it's 50 miles long it's a mile wide long and narrow and you go okay that's kind of weird uh well we got lake roosevelt that's long and narrow right how did that form well we put a grand coulee dam on right and we we backed up the columbia and that's why lake roosevelt exists banks lake that's long and kind of narrow what's that build a dam pump a bunch of water into the upper grand coulee you've got banks lake is lake chelan the same story well there is a dam in chelan they built it in the 1920s it raised the level of lake chelan by about 20 feet but that's not why lake chelan exists lake chelan is the third deepest lake in the united states you don't get a lake like that that deep by just damming a river right crater lake in oregon deepest lake in the u.s almost two thousand feet deep lake tahoe in nevada and number three is us lake chelan how did that thing form it's deeper than lake superior it's deeper than lake pondere up in northern idaho so what is the story if you guessed glacier you're right but if that's all you want you're just a self-satisfied nod okay yes yeah lake chelan was formed by a glacier we're moving on that's not enough for us tonight how did this lake form in the ice age which glacier was it where did the ice come from how thick was the ice did the ice come down from wherever multiple times is it possible there was more than one glacier because we need to make a deep hole this lake is so deep that the bottom of lake chelan is below sea level by hundreds of feet fresh water lake chelan a hole that's below sea level who the hell did that digging ice but when and why and how all right so let's look in the neighborhood uh the drainage to the south is the wenatchee river the drainage further south than that let's put one at you here the drainage to the south of that is the yakima river coming right past this building here are there lakes in the yakima river drainage and the wenatchee river drainage there are there's a little lake upstream of us like ketulus that's the result of a glacier is there a lake in this wenatchee river drainage there is lake wenatchee the result of a glacier but those glaciers let me use white here those glaciers are fingers of ice alpine glaciers coming out of the mountains and so if we're looking down on an alpine glacier this geology 101 now we're looking down on an alpine glacier this is a map of an alpine glacier you got it if we do that and the glacier brings a bunch of rocks down and drops them and makes a ridge that's called a moraine made out of loose glacial rocks and then if we melt that ice back we are left with that moraine and we can get a lake ponded behind that glacial moraine it's kind of like damning just like we were talking about before a natural ice age dam of moraine material and so that's the story here that's the story here but we don't have a lake chelan the wenatchee valley doesn't have a lake chelan we need that deep hole is there something else going on there is lake chelan is not the result of an alpine glacier coming out of the mountains and that's what i assumed up until a couple years ago i teach washington geology for a living and i just assumed there was alpine ice coming out of the cascades making lake chelan it's not true and i'll show you the evidence it's not true well if it's not an alpine glacier what other choice do we have it is ice right yes it is what do you got right the ice sheet we are far enough north in washington to have an ice sheet come down and somehow create lake chelan so here's the ice sheet here's the ice sheet here's the ice sheet this is the canadian ice sheet this is the same ice sheet that's over most of canada this is the ice sheet that came down to wisconsin came down into new england and this is the ice sheet during the ice age multiple advance and retreats by the way not just one but each time we advanced this ice sheet it got over seattle 3000 feet of ice over seattle that's the ice sheet that same ice sheet is thousands of feet thick over the okanagan in upper northern washington that's our topic in just a second this same ice sheet is making an ice dam in northern idaho pondere but also making the ice dam for the missoula floods and all that so it's that same ice sheet through this whole story that ice sheet created lake chelan so i didn't draw this well enough did i because i've got lake chelan here and i've got this ice sheet here so let me make an adjustment and get that ice as far enough south so that we can get it into the lake chelan area okay we're making progress lake chelan is the result of this ice sheet somehow but you may be confused and i think you should be how specifically is that ice sheet doing that here's the kicker here's the clever idea in geology 101 land you either have a continental glacier crossing flat terrain or you have an alpine glacier little ribbons of ice coming down a mountain valley what happens or is it possible for you to take a thick ice sheet and have it invade the mountains it is possible and that's the key concept we want it is rugged mountainous terrain in the north cascades national park and there is beautiful evidence compiled by mainly one guy guy named john riedel we're going to meet him tonight with a little video clip he's the glacial geologist for north cascades national park wonderful fellow and john's work for the last three decades has been to find evidence of the canadian ice sheet plowing into the mountains not beveling off the mountains but flowing into the mountains and the ice sheet is so thick in places that it's literally crossing mountain ridges and going from one divide to the next he's got beautiful evidence for this and here's the reason we're talking about it tonight an arm of that ice sheet from canada found its way through a low spot rainy pass do you know it if you take in state route 20 over the north cascades rainey pass is one of those passes there's an arm of that ice sheet let me do this there's an arm of that ice sheet that crossed into the valley up lake from staheken do you know staheken the upper end of lake chelan so on the cascade side of lake chelan there's an alpine rong there's an ice sheet arm that's coming through the mountains through a low spot and basically it's an arm of the ice sheet that's masquerading as an alpine glacier it's where an alpine glacier would flow but it's way more ice i've got a dimension for you that masquerading arm of ice sheet was five thousand feet deep five thousand feet of ice an arm of the ice sheet flowing into this mountain trough that gets our hole deep enough especially when we can find some soft bedrock and you go huh i guess that's interesting i was expecting more you want more i'll give you more the last part of this is even more unbelievable there was another arm of this ice sheet the okanagan ice sheet that flowed up the lake let me repeat lake chelan was formed by a glacier not an alpine glacier a continental ice sheet that came from canada but it wasn't just one advance of the ice sheet it was two independent arms of the ice sheet coming from both ends of the lake and having a digging contest essentially who can dig deeper to make this hole that's below sea level now that i like and maybe you do too and that's mainly john riedel's story but if it's a story and it's against the grain and it's against conventional wisdom you better have some good evidence for you i've got a bunch of evidence for you with the visuals in just a second but let me give you one key piece of evidence that might work for you on the chalkboards here you okay you doing okay can i get you some hot tea or something all right let's make a lake map real quick we'll see how this works it's all free hands all free styling bob dylan freewheeling geology oh lord all right that'll do the city of chelan is down here that's a capital c manson is right here with all the apple orchards there's a little kink in lake chelan this is the narrows the lake it's narrow there's a history of landsliding in there and then the long stretch of the upper lake let's call this the upper lake and the lower lake okay stehekin is up here you take the lady of the lake all the way up to the end of the lake holden village out here if you go out take out at lucerne with me the deepest part of the lake is right in here let's come back to that in a second but i want to plot these two arms of the ice sheet for you with you and i need to show you one convincing piece of evidence that we really had those two arms of the ice sheet and then we'll move on to something else you ready here we go here's the arm of the ice sheet coming out of the cascades the ice sheet that's masquerading as an alpine glacier and what rocks are it bringing what rocks is this alpine sheep bringing it's bringing cascade rocks it's coming from the cascades man so we're going to do a bunch of this open circles open circles moraine glacial till open circles open circles indicating cascade rocks lava rocks volcanic rocks granites things that we can pick up loose here and then go yep those are from bedrock up the valley that's what we'd expect probably that even could be an alpine glacier here's the cool part the okanagan ice sheet the arm of the ice sheet that came from the east was bringing different rocks was bearing different gifts for lake chelan i don't have time to make them all but i'm going to make dark filled in circles any guesses what that is right that's basalt each of these erratics these are erratics too big boulders dropped by the ice each of these boulders is basalt and you're like so what here's why it's important there is no basalt bedrock in the cascades hardly any essentially none and we've got thousands of these basalt rocks uh down lake from the narrows that's the evidence that the arm of the ice sheet coming from the east invaded from the east crossed the columbia river came off of the waterville plateau and pushed up the lake why if you go east of the columbia river in the chelan area it's all flood basalt it's layer after layer after layer of german chocolate cake of brown lava rock basalt and so this beautiful transition from erratics glacial erratics that are granitic and volcanic light-colored volcanic to transition here where we have these basalts and nothing but basalts that's a key piece of evidence we had these two invading guys how you feeling moving on moving on i don't care how you feel we're moving on just kidding i want to keep this beautiful map but i want to get rid of the ice and as promised i want to say just a little bit about the bedrock which you know i had high hopes for this lecture i thought i could do a ton with this bedrock because it's a very complicated area and the dirty little secret is i kind of gave up it's so complicated i was just looking for basic messages and i i got help from people by email who know these things and a couple guys i work with and i can't even do basic stuff it's so complicated so i think what i'd like to do is at least comment on why this lake is so deep where it is in other words why did that ice dig so successfully just up late from the narrows and then i want to highlight something called a migmatite which i think will do better on the visuals than we are here so let's start with uh yeah let's start with this so schist is a metamorphic rock that is typically softer than other metamorphic rocks so if you lose it with the rest of this bedrock stuff this is the main message schist is relatively soft rock it's not an accident that the lake chelan trough is the deepest where the ice is dealing with schist it was easier digging there up lake it's mostly a metamorphic rock called nice which is harder physically harder more resistant to erosion it's got a different story to tell and down lake there is something called migmatite and a few of you are like i thought i knew geology i thought i was really a geology enthusiast just like old jerry i've never heard enbigmatite you say it's not common but it's a featured bedrock piece in the lake chelan area this is actually called the chelan migmatite complex what is it well if you ever go to an ice cream place to serve soft cell ice cream and you're waiting in line and you're like oh god when i get up there i really got to make a decision now what kind of ice cream am i going to get what kind of ice cream i don't know do i want vanilla do i want chocolate somebody help me out i can't tell i i don't know i'm going to start panicking here and somebody just says i just get a swirl make it easy on yourself just get a swirl chocolate and vanilla together and that's really what a migmatite is it's a swirl you'll see the pictures i'm not exaggerating it's a swirl of igneous and metamorphic rocks all swirled together and the temperatures and pressures were such that those two very different kinds of things igneous and metamorphic rocks can be all swirled together just like a soft-serve swirl cone so a migmatite swirl i want to do just a couple more things with this again i had high hopes i don't have them anymore i've been beaten down by the complicated bedrock of the lake chelan area there is more schist over here basically down river now the columbia river is over here right so if we're driving down river from chelan to wenatchee we'll leave the migmatite eventually you'll know what it looks like in just a second if you already don't have it in your head we'll get into some schist and down river of that i didn't plan my spacing very well is another nice that's right above or right to the north of wenatchee so you'll notice that there's a lot of metamorphic rock here here are the basic things i want to say before we move on to the earthquake discussion so this was supposed to be the whole part of the lecture it's been whittled down to five to ten minutes at most some of these are for sure exotic terrains pieces of crust that were made elsewhere and then added to north america somehow and whether they just came in offshore at our latitude or whether they literally came from the south from california originally or even mexico and then shifted north that's a whole not another part of this discussion but it is looking like these starred guys here i think even this one are for sure exotic terrains they were not made here the ages i could give you but they're different from their neighbors the temperature and pressure conditions of creating these are different from their neighbors it's a jigsaw puzzle and every one of these is a separate jigsaw puzzle that has its own story to tell now before this summer i assumed that the chelan migmatite complex was a terrain as well and it may very well be but there's a chance it's not and that's what i want to do before i move to the earthquake discussion i want to draw a sketch quickly of why this migmatite is very special to us very worth our attention by the way we'll throw in some younger 50 million-year-old-ish granite plutons blobs of liquid coming up once these terrains or other blocks are here and about the time 50 million years ish or so there's a beautiful set of dykes feeder dykes most of them mafic meaning dark colored but some of them lighter colored or felsic as well these eocene dikes have a story to tell as well and we'll comment on those with the visuals but migmatite what's so important what's so important what's the visual we want for them you hanging in there bedrock man complicated thankfully i work with a guy named chris mattinson who is here tonight and he um has spent many decades on the chelan migmatite complex his dad studied it first back in the 70s and and this is the visual that chris was able to pass along to many of us on a field trip recently let's put the chelan migmatite conflicts the swirl into some sort of context uh all right so geology 101 land we have a volcano and a volcano has a plumbing system it's a underground room it's full of magma magma liquid magma fine and then down below that much deeper there's a boundary between the mantle and the crust of the earth and usually not discussed is what's going on down below that room in the deepest level of the cross what's going on down there normally that's a i don't know shrug but the chelan migmatite complex that swirl is a rare opportunity to get your nose right on rock that was forming here in other words this is where the sausage is made to mix you know we had ice cream and now we have sausage but hopefully you get the idea there's something going on down here where we're actually squeezing out the rock we're actually generating the magma that's going to fill this reservoir and this swirling we'll use another color this swirling going on down here is under extreme temperature and pressure the migmatite forms here last sketch for you this is a cross section here's chelan here's bridgeport some of you know the lay of the land up there this is the columbia river flowing essentially uh north to south essentially there is the potential let me do this differently when we cool off this system and we turn the magma to granite and we cool off this system and we have the swirl harden into rock it is possible and this is a future project that's in the work it is possible that the granitic rock of the brewster area and the chelan migmatite complex are one story originally like this here's the granite here's the swirl magmatite if we take that and just tip it on its side perhaps that's what we're talking about here why is that important well on most of the geologic maps today the geologists have said okanagan batholith chalan migmatite complex two separate animals two separate terrains are definitely two separate blocks of crust chris mattinson and some colleagues over the next five years are hoping to find enough chemistry details to tie these guys together and try to make at least one small step forward to simplify and make this area a little bit more comprehensive last thing before we go to the visuals i'll just do it verbally the greatest earthquake in washington recorded history basically since the civil war we've had one huge earthquake recorded it happened in 1872 it happened in 1872 he goes to his notes december 15 1872 9 14 pm estimated magnitude 7.4 someplace in the lake chelan area between 1872 and essentially three years ago 2014 it was a mystery as to where that earthquake happened washington especially northern washington in 1872 was incredibly sparsely populated just a few log cabins a few scattered pioneer homes most native americans who are passing things along orally of course but nobody writing things down there aren't even any local newspapers in 1972. you got to go to walla walla or olympia to find a newspaper account but from those newspapers outside of the region it was clear there was a doozy felt across the entire pacific northwest and until just a few years ago that was a complete mystery as to where that 1872 quake struck we now know there was a beautiful discovery three years ago and i'll show you with the visuals where that fault is where the ground broke and i'm afraid the bad news is those kinds of faults are still alive they're still active and so we are concerned that a repeat of something like the 1872 is in our near future and you want to know exactly when we don't know but the main message is that earthquake a big one potentially 7.4 happened in eastern washington on a fault very similar to faults that are all through this area in ellensburg so let's look at that too to the visuals we go okay let's go ahead and jump in we need the visuals right the chalkboard only gets us so far let's go to some visuals so we leave ellensburg you are here and we're going here look at that look at how long and thin that lake is kind of looks like roosevelt kind of looks like banks but we know this is a different story this is a glacial story yeah take us 97 get over to the columbia river head up to chelan why not there's all sorts of reasons to go up there it's a vacation place people have second homes they have third homes in the chelan area look at that why wouldn't you go to a lake like this oh sure we can go drink beer we can we can drink hard cider we can do winery tours et cetera we can play a little golf there's all sorts of reasons to come to this area and the town of chelan is on the down lake side there's a long history there and if you can work your way along the shore you can only drive along a portion of lake chelan look at that history going back with agriculture and orchards and irrigation and power electricity so the chelan fruit is still a big part of the manson area on the lower lake edge chelan fruit all over the place the apple cup cafe why not drop in and have a little cup of joe in chelan itself and all these beautiful old fruit labels i'm a fan of those in general but the lake chalene area has that in spades if you want to jump on a boat and go all the way up to the head of the lake 50 mile journey you can do that and get up to staheken get yourself through the narrows and learn about the shorelines and watch how the shoreline changes up at staheke and the landing is there it's a point of entry to the north cascades and uh you bet recreation boat docks complicated rocks and uh why not look at a few beautiful scenes from lake chelan itself fresh water deep lake you betcha oh sure i got some money i live in seattle i'm tired of the rain i'm going to spend weekends over in chelan i got my own doc and my neighbor we've all got boats we're going to just party up there man that's the scene lake chelan but we're here to talk about the geology not that other shenanigans and the geology is on display wherever you look and as we've already talked about with the chalkboards way more than the glacial story chelan the town the narrows landslides and working our way up the lake it's a desert today down the light the the low end of the lake there's sagebrush and that makes it nice for us here's that dam it's not a big one and remember this only raised the level of the lake 20 feet in the 1920s probably mostly for irrigation although i'm really making that up but there was a deep lake long before this dam was created all right good that's the setting for lake chelan now is the lake glacial like walawa lake which is in northeast oregon there was an alpine glacier that came out of the wild mountains and look at this beautiful moraine this is what i was trying to draw on the chalkboard which is not the case for lake chelan but i guess most people would assume this might be the case that you have a lake from a glacier the ice pushed its way down alpine ice the ice melts back and the water is trapped behind a moraine that's common for lakes created by glaciers but that is not the story for lake chelan right let's slow down and look at this very carefully uh so the town of wenatchee is here you're like where's lake chelan it's not on the map this is a map during the ice age and lake chelan is under this ice what is this ice ice sheet from canada masquerading as an alpine glacier so can you see that the portrayal of this ice sheet is different than the portrayal of these individual little alpine glaciers i know they're all white but hopefully you can see they're showing this different than this that's a main part of tonight's lecture alpine ice making dinky little lakes making dinky little moraines major ice sheet arm and major ice sheet arm and the battle of the two arms to dig and form a basin that is hundreds of feet below sea level look at that sheer wall ice sheet cutting as opposed to alpine cutting and multiple advances in retreats i keep saying that but that's important to remember it wasn't just one advance and retreat of the ice we got two and a half million years to play with this is a brand new figure from john riedel the guy who i mentioned from north cascades we'll meet him momentarily and i love this map i hadn't seen it until last night he just emailed it to me generously and here is the terminal moraine which is on the southern margin margin of lake chelan and you can see again we're having the continental ice invade the cascades now what does that look like hopefully this works for you this is a classic north cascade shot i just snapped this out of an airplane window as we were approaching seattle from the east and each of these little valleys had an alpine glacier in it so it's a u-shaped valley and i want you to pay particular attention to these ridges look at how razor sharp these ridges are that's normal these are called eretz steep razor sharp ridges from alpine glaciers carving and a next door neighbor and a next door neighbor and they're all carving multiple times but john says if you're thoroughly wide awake in the north cascades there are plenty of ridges that are not razor sharp they're beveled off they've been rounded over something crossed the razor sharp ridge and screwed it up and photos like this are all through john's presentations john rito from north cascades national park look at this ice flowing ice sheet flowing from left to right ice sheet sculpting this formerly razor sharp ridge and beveling it over this is ice sheet crossing divides and eventually it's this ice sheet that's going to find its way to the chelan valley the chelan river valley that no longer has a river in it it's got a lake now in addition to those beveled ridges which i just love of course there's glacial till of course there's rocks that are big and loose and they were transported only by glacial ice but this could be alpine or continental it doesn't have to be continental this is how thick the glacial tail is right above dropping into lake chelan and there's an ice age flood story i want to mention briefly here before we quit don't let me forget that so more glacial till mostly cascade rocks here now if we're hiking up above chelan the town this is the chelan butte area my wife and i were up there over veterans day weekend just a couple months ago and didn't really know we're doing but we just found a public trail and just started wandering it's a great trail kind of like monash ridge here in the valley lots of people on it on a holiday weekend but notice how sculpted notice how weird this face looks this is almost like somebody dragging their fingers along the side of a stick of butter it's the ice that did that it's the canadian ice sheet that did that and sculpted these hills above chelan to us in geology that's just screams glacial activity more than the lake itself this sculpted landscape and the steepness of those slopes and then of course all this glacial till all these loose rocks that are up there on tops of the ridges how'd they get there otherwise you don't normally get piles of loose rocks on top of ridges unless you have a thick glacier leaving rocks that were brought in from elsewhere you're starting to see the picture now isn't it handy to have actual photographs instead of a caveman drawings on a chalkboard that only gets us so far again the sculpted this is mostly erosional in my interpretation but there's also some cane terraces up there as well some little deposits along the former margin of the ice uh-huh uh-huh right we go 386 feet below sea level the the floor of lake chelan itself that's a deep sucker now the idea that i forgot to mention and i actually forgot if i have a slide for it but i just want to throw it in case i forget there were times that the masquerading ice sheet you know what i mean and the ice sheet coming up lake didn't touch and there was actually times where we had water between both arms of the continental glaciers water in the trough that had nowhere to go and the water was ponded higher and higher until that glacial lake chelan this body of water halfway in the trough was 700 feet above its current level if you get water that high in that trough you're going to have spilling you're going to have an ice age flood water in glacial lakeshore land spilling to the south do you know navarre coulee or nap they have roads in them today those are two roads you can get to the lake those roads those coulees navarre coulee and napoli had ice age flood water coming down which is basically glacial-like chelan water spilling to the south pretty cool now the evidence of how we know the ice pushed in from the east as well as from the west what's the evidence we cross this brown stuff which many of you know is flood basalt these are lavas that happen millions of years before the ice age and the cracks are here the lava came out it was orange syrup essentially and notice that chelan and lake chelan are not in that basaltic scene it's to the east of the lake and if you get up on the waterville plateau there's wheat fields it's like a different country and you're right next door to the columbia river why because you're on those basaltic plains essentially why is that important well here comes our ice sheet from the east the okanagan lobe and it's going to approach lake chelan from the east remember and what's the significance it's going to pick up german chocolate cake chunks basalt it's going to carry those basalt chunks into the chelan trough and drop them glacial erratics that are basaltic like these guys this is jaeger rock we're still up on the waterville plateau but i want to give you some photos of some classic basalt glacial erratics that the ice sheet picked up and moved just a few miles and then dropped up on the waterville plateau but what happens if you have that ice pick up the basalt head west across the columbia and enter the lower part of lake chelan this best photo i got for you tonight do you like it this is mcneil canyon we're just across the columbia river from chelan we're to the east of chelan and these are the beautiful basalt glacial erratics they look like they were just let down on a string from heaven don't they they didn't come from heaven they came from the okanagan lobe the ice from the east brought these guys in and if you're in the lower part of lake chelan and the hills above the lower part of lake chelan there's many more of these basalt rocks if that's not enough for you look at the thickness we have 400 feet of glacial rocks loose glacial rocks under the town of chelan this is all from the okanagan lobe as well this is also from the arm of the ice sheet coming in from the east who knew not me certainly until i went on john riedel's field trip a couple years ago that pile of 400 feet of okanagan drift we call it has been cut more recently by a little chelan river that only goes a couple of miles and takes a little bit of water from the basin and gets it down to the columbia river okay we got we have it now the ice sheet story i hope you do here's our lake white is all the ice sheet from canada hope you're feeling good about that way more than you probably had 45 minutes ago at least i'm hoping that's the case uh let's meet john riedel briefly in this beautiful little artsy film and get a sense of what he's about glaciers are elders of the landscape the rhythms of the mountains recorded by glaciers are cycles of climatic change they are the annual rhythms of seasons climatic cycles spanning tens of thousands of years the ultimate force shaping the mountains causing change to land and life despite this power the rhythms are imperceptible the beat slow and complicated but inexorable it can be seen and heard only by those who take the time to look and listen for them i have had the privilege and the resources as a geologist to listen and learn [Music] john riedel neat guy from wisconsin you can't be all bad if you're from wisconsin right all right uh there is a little bit of ice age flood story i'd like to touch on before we leave the glacial action when the okanagan lobe is there and we know its role now it's helping to form glacial excuse me it's helping to form lake chelan the missoula flood water coming across washington is not allowed to get to chelan when this ice sheet is in place and so the missoula flood waters are diverted to cut the grand coulee the missoula flood waters are diverted over dry falls the missoula flood waters get ourselves down to quincy basin so many of you know that story it's interesting to lay this story in this is happening basically at the same time each time we have the okanagan lobe but when we finally melt the okanagan low back we can get a few at least missoula floods coming all the way down the columbia river and those missoula floods are coming right near chelan not over chelan but down the columbia river at chelan so missoula flood's cutting the grand coulee missoula flood's cut in the grand coulee when the ice sheet is there when it's not we can have the ice age floods come down the columbia this is a nice map from jennifer hackett again showing our ice sheet chelan lake chelan under the ice and this is the map of the columbia river in between ice age flood events and the columbia river went cooley city moses lake almost othello around the north face of the saddle mountains get to beverly hang a left and then continue down the columbia valley that we know and love today this is ice age flood water coming down over wenatchee again we need the okanagan lobe out of the way those beautiful missoula floods coming down the columbia they were monster floods leaving giant current ripples like this downstream from wenatchee but back up in the chelan area this whole columbia river scene is right next door to chelan and lake chelan just off the frame to the left okay transition time let's go to the bedrock now look at this bedrock these are grad students uh their first experience they have when they show up to study here as graduate students here at ellensburg at our department central washington university they're coming from all different parts of the country and we take them out in the field right off the bat it's labor day-ish and we take them out and sometimes those field trips last a long time they age they age quite a bit by the time they're done with that experience but they learn a lot that's what's important matt from eric cheney to show us simplified flood basalts and now we realize look at the look at the jigsaw puzzle look at these blocks that all have their own story to tell i mean i wish i could do more and part of it is me being limited in my knowledge and much of it is we still don't have a basic story figured out for all these little pieces maybe some day but not now well now we're interested in the rocks and we're interested in the migmatite and the schist so there are places where there's not glacial tilt but there's actual bedrock popping out of these ridges and that's where we're going now aha migmatites swirl swirl mixture of what migmatite that's right igneous and metamorphic rocks look at that are you kidding me can you think of a place in washington that has more beautiful complicated rocks that are so accessible this is driving right up 97 or 97 alternative if you are alternative yeah it should be more of a swirl like that when we really start looking at the details of these migmatites so this is from a field trip led by this fellow chris mattenson who i work with here at the college in ellensburg and he is an authority on this migmatite and he has done a beautiful job of piecing a lot of this history together and i feel confident with the chelan migmatite complex mainly because of my learning from chris directly and he continues his work remember he's the guy that's going to try to link the okanagan batholith or the okanagan granite with the chelan migmatite if the data allows so here's chris in action look at charts like that look at how complicated look at how swirled look at how there's like multiple generations but remember the main point these are rocks that were in the deep crust this migmatite was developing and forming i'm not exaggerating now 18 miles below the surface this is where the sausage is being made this is where the magmas are first being developed before we push that magma up into a magma chamber and that migmatite that deep rock had to eventually get back to us right had to be lifted 18 kilometers and we've got good evidence that that deep crustal migmatite in the chilan area was brought way back to the surface 18 mile journey and got up here by at least 50 million years ago because of those plutons those those granites and those dikes that are cutting through at shallow levels so look at the complication here this is my sketch i was trying to make sense of chris gave us these photos of just one outcrop with these you know this is where they put the dynamite in to blast a a road cut this is just north of chelan on 97 on the way up to pateros and you can spend hours just trying to piece that story together just relative age dating which of these is first second third fourth fifth and again you're trying to reconstruct this whole sequence 18 miles below there's another outcrop this is do you know this road this is going from columbia river climbing up to the town of chelan and this beautiful face which wasn't there until uh i think somebody said in the 50s or 60s but i don't really know anyway a beautiful face that is one of the best outcrops in the state especially for learning about complicated metamorphic rocks like migmatites and then along the lake itself you know dying light of the day on a hot september day and chris is still at it with all these details in the magmatite itself gorgeous stuff wouldn't you say you can appreciate it at least visually if not geologically that's kind of where i am to do i still don't have a whole lot figured out about the details and very few people do you got to be pretty bright pretty bright to read each of these metamorphic minerals and come up with certain temperatures and pressure conditions so we'll just stand back and be at awe with all these kinds of cooling histories and pulses of magmatism and metamorphism from this magmatite migmatite excuse me migmatite hey a pen from cwu for scale all right there's different pulses of action within this migmatite the big message is the protolith or the original rock that was then squirreled up and swirled up at deep levels has been dated at 165 million years old that's way older than these other terrains in the neighborhood so compared to its neighbors the chelan migmaton complex is not only deep but impressively old compared to its neighbors and what does that tell us does that tell us that this is somebody else's crust in other words an exotic terrain or does that mean this is originally some stuff in washington that has been swirled up unclear to me unclear to most at this point thank you chris for these diagrams wish i understood everything in them i'm sharing them anyway nice teaching choice right teaching stuff you don't even understand great i will say one more thing about the migmatite you can take a grain of zircon a zircon is a mineral you can take a grain of zircon that's the size of a sand grain and you can with techniques that now chris has mastered and instrumentation that chris now has in our new science building and drill holes essentially in this little grain of sand again it's a zircon from the migmatite and you can get different ages from different portions of that little grain of zircon to then tease out different changes different times of metamorphisms different parts of the history of that swirled rock staggering thank you land migmatite complex we're moving on so chelan that's the migmatite here up by brewster is this granitic rock remember the chalkboard sketch maybe this is the magma chamber and this is the plumbing system below the magma chamber and maybe they're lying on their side along the columbia river between brewster and chelan let's go to a couple other neighboring blocks and then we'll transition with the final comments we have for the earthquake story this is the nepiqua complex it's a schist that's just to the south of the chelan migmatite it for sure is an exotic terrain interpreted as sediment that was originally on the floor of a deep ocean and was somehow transported from a deep ocean to the area of ineot just south of chopin now how do you do that you take stuff on the ocean you convert it into rock number one then you get a metamorphic rock number two then you somehow get it into interior washington and oh by the way you know a few thousand feet above sea level good lord there are stories to tell and that's the complication and that's the intrigue of these very impressive uh swirled rocks as well this is just up the ennea river from the columbia if you're interested in seeing this right along the road finally the suakane nice the soaking biotite nice which is further south yet now we're approaching wenatchee this is also available along the columbia and this is interpreted as sediment sand primarily that was originally deposited in an oceanic trench again it's got to be a terrain it was originally out in the ocean somewhere in a deep trench we take that sediment we convert it into nice and we get it here to central washington am i blowing your mind have you heard about this terrain stuff before boy if i ever get gutsy enough we'll do a bunch of lectures on these but boy you really have to eat your wheaties to put this all together schwa cane biotite and ice some granite's up there i think we're done oh no we got one more thing so cutting through all of that uh old rock are these dikes these feeder dikes that i got really intrigued by when we were on the trip in september here's it feeder dyke cutting across 50 million years old roughly 50 much younger than the rocks themselves so we have to crack these rocks somehow and send these squirts of mostly dark colored stuff up through them we call it a mafic feeder dike and some of you are nodding your head because you know about mafic feeder dikes there's mafic feeder dikes north of ellensburg in the liberty area there's mafic feeder dikes that are much younger in the columbia basalts of southeast washington the point is these mafic dikes are the same age and potentially the same composition as the feeder dikes in the liberty area i'm not saying there's gold here but i am saying that there is a more regional extent to these eocene feeder dikes that i didn't understand before until last september even this famous place called ribbon cliffs which we're going to talk about in just a second has ribbons in it because these are the mafic feeder dykes that appear to be part of the same feeder deck story of the liberty area brand new to me by the way maybe to you too feeder ducks in the tiana way and all these feeder dikes with about the same orientation and northeast orientation up through the chelan area see this is close to home this is us mount stewart and these feeder decks cutting through we've already talked about those in previous lectures these feeder dikes coming through the stewart batholith i'm saying the feeder dykes up by chelan potentially are the same story oh by the way you can take some of these terrains and cut them in half it's not enough that they come in from the ocean once you get them here let's let's cut them up again and let's send some of them further north good lord oh i can't even look at that i'm getting a headache there are books that help general audience books geology of the north cascades is beautifully written by ralph haggarud and roland tabor and i highly recommend it it's more than 10 years old now but it's still beautifully done to at least make a first attempt at saying some regional things about the north cascades okay the last section of our lecture is talking about earthquakes this is seattle in 1949 but i want to talk about a bigger earthquake than this the earthquake that happened in december of 1872. for many years you would just travel along the columbia river north of wenatchee heading to chelan and some of you on the from the west side of the river you would know this place called earthquake point and they would talk about again ribbon cliffs where this is where a mountain broke in half and half of the mountain fell and slid into the columbia river in 1872 due to an earthquake and blocked the columbia river and there are native american accounts of that actually happening and in the river are still major blocks of that slide that landslide where half the mountain broke and fell here we've got it can you see it mountain half is too strong but a portion of the ridge broke and kerplunked and this is before dams were on the columbia river of course and so the river was dammed oh we got somebody jet skiing on a hot summer day right in front of the broken face it's this where we have the most exciting evidence of this earthquake but this is not where the fault is this is not where the ground actually broke and all the seismic energy came away it must be close to this perhaps but not the actual fault that was the mystery for so long this is a map basically estimating a magnitude of 7.4 and a map from all the general newspapers at the time recording what people experienced across the pacific northwest again to try to find where this earthquake actually happened where was ground zero for this big earthquake in eastern washington if it was in eastern washington this is an account i'll read you just part of it from thorpe which is just a little town outside of this town of ellensburg this guy says a severe shock of earthquake is being felt this morning in other words an aftershock but the last night at 10 o'clock old mother earth was being shaken from the west to the east not true turns out throwing all the poultry from their roost frightening the dogs cats horses cattle stopping clocks jarring chimneys from their foundation so that's in our valley this guy experiencing that in walla walla a low rumbling noise was heard rattling windows swinging picture frames in yakima uh the earthquake at that place was quite severe there were three distinct shocks the indians on rock island near wenatchee say the mountain at that place rolled down and killed three persons that's probably ribbon cliffs it's kwame passed people were shook off their feet they were standing at snokomi pass they were knocked to the ground in yakima people rushed out of the doors in a great state of alarm with clubs revolvers and shotguns thinking the indians had made a general attack and we're tearing up things generally all right let's continue windows shattered in victoria bc chimneys cracked in olympia trees toppled and puyallup dishes crashed in seattle and my personal favorite a lighthouse near port angeles rocked to and fro most alarmingly and was severely damaged where the hell is this earthquake is it really 7.4 magnitude did it really happen in eastern washington in effect all these regions felt as far away as northern california again that was the mystery for a hundred years and more from 1872 until just a couple of years ago so for many years all geologists could do was to say well probably up in the chelan area probably in that circle based on these reports and a couple of basic field observations but that circle persisted for many years and of course every generation you'd have a an enterprising enterprising kind of youthful geologist going i can figure this out i can find this fault we got to find this thing man and as i mentioned just two or three years ago brian sherrod from the usgs who has a new tool that previous geologists did not he has something called lidar some of you know about it you have these beautiful images of the land surface and you can magically remove all the vegetation you can remove everything and you can get a very detailed image of what the ground looks like and sherrod started looking sitting at his desk in his office started looking at all these lidar maps these lidar imagery sets coming in and he was actively looking for places where it looked like there was a fresh break in the ground and he found a place that was worth investigating it's a place called spencer canyon so we are looking west across the columbia at a rondo can you picture where that is let me help you out so here's uh the town of waterville we're on u.s highway 2 we're dropping west down to the columbia that's quite a grade that you go down and then most of us hang a left when we get to orondo and follow 97 down to wenatchee i'm saying across the river from from arondo across the columbia river this little canyon spencer canyon there's no road in there is where the ground broke in 1872. it's rugged so sherrod and a few of his buddies including a guy that lives in town here john lasher who is here tonight guarding on foot and maybe some old four-wheel drive vehicles up into spencer canyon so this is lasher taking a photo in rugged spencer canyon looking back now to the east you got your bearings arondo the river's right down here and here's us2 climbing to waterville and eventually coulee city you got it so using the lidar from spencer canyon a scarp a place where the ground was suddenly broken clean was identified and that lidar you can imagine how much lighter you need to go through you're looking for a needle in a haystack essentially but that scarp was found it looks like this in the imagery so that's not enough evidence you just see a little crack so you got to go there and you've got to dig a trench you've got to dig a trench you actually literally have to dig a trench perpendicular to the trace of the scarp and try to find some layers that you can date if you know the ages of the layers that have been broken you can say something about how frequently the ground is going look at this thing and again this attracted shared this is a landslide looks pretty darn fresh the ground broke here and this material flowed potentially in 1872 says sherid so we not only have a scarp that's pretty fresh but we have at least one debris flow of some sort so just to put this in general context we're talking about shallow earthquakes now with this 1872 event we're not talking about magnitude 9 we're not talking about deep things like nisqually or 1965 we're talking about shallow crustal faults the most famous of which is the seattle fault but if you get over to eastern washington some of those shallow crustal faults exist as well and it turns out the area between wenatchee and chelan has been very seismically active in the last 150 years no killer quakes this is the 1872 by the way the bigger the circle the bigger the earthquake but notice how many moderate earthquakes have been in what's known as the chelan seismic zone if you talk to somebody born and raised in indiana or rondo they have many little shakes that they can remember and if they're a fan of seismic stations there are thousands that have been recorded but too small to feel why are all these earthquakes happening at shallow levels the real basic message is washington is getting crunched it's getting squeezed between western washington generally moving actively to the northeast against this portion of washington that's basically not moving very well so you've got slamming against non-moving and you've crunching this kind of general zone here's an animation to help you see that it's going to go in motion in just a second the motion of the pacific plate and the juan de fuca plate are driving this clockwise rotation of the crust from california to western washington and all of that is moving against stable northern washington as a result we keep having these shallow crustal earthquakes like the 1872 and the potential is to have something that big again again yellow dots are earthquakes look at this cluster between wenatchee and chelan and the biggest circle again is our 1872 quake that was a mystery we've got faults by the way these are reverse faults that are that are developing these earthquakes uh this is south of ellensburg on the way to yakuma so boy there's there's there's there's some history of earthquakes in eastern washington and we are just starting to comprehend the significance of them i don't want to freak anybody out we don't have enough dates to be able to predict how frequently these earthquakes happen in eastern washington but um the potential is there for more concern than we have now let's put it that way that fault was just on the way to yakima okay finishing up i promise you maybe had about enough and let's wrap it up so up in the lake chelan area we're squeezing the crust that's responsible for this let's actually get into spencer canyon and see what that scarp looks like up close it's right here running across the side of the hill and in the general area there's some more of this ribbony cliffy stuff these eocene feeder dikes but that's not part of the earthquake scarp itself instead look at that that's where the ground broke in 1872 on that winter night after nine o'clock on december whatever 1872 and to build the trench to dig the trench it was too steep to get any sort of bobcat or any sort of backhoe up in there so a bunch of these guys these geologists with all these advanced degrees grabbed a bunch of shovels they dug a trench by hand and they needed that trench brian sherrod the leader of this little organization and john lasher who lives in town here who was a citizen geologist to help out he's also good with heavy machinery although they couldn't use it on that occasion they dug this by hand and they needed to find layers underground that were clearly broken by this scarp and then if you get the ages on the layers you can say something about when the ground broke or if you had repeated failures so this was exciting to many of us because a mystery has been solved not why the earthquake happened but where the earthquake happened we actually finally have the smoking gun for the big quote-unquote chalan earthquake of 1872. it wasn't in lake chelan itself it was to the south in spencer canyon so thanks to brian sheridan and harvey kelsey and a few others that were involved in that work so we've got all sorts of things hopefully jerry is pleased by now we've got the lake we've got the rock types we've got the terrains and we have this fault in spencer canyon putting a little cherry on the top of the cake or whatever the analogy is we thank you lake chelan for all of your wonderful geology and i thank you all tonight for coming thank you very much appreciate it

Channel: Nick Zentner

Views: 6,107

Rating: 4.9565215 out of 5

Keywords: Nick Zentner, Lake Chelan, Lake Chelan Geology, Okanogan Lobe, glacial erratic

Id: qnAqzTBOPnM

Length: 67min 18sec (4038 seconds)

Published: Mon Mar 15 2021