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Posts Tagged ‘Chelan WA’

Lake Chelan, Washington

Posted by graywacke on November 24, 2017

First timer?  In this formerly once-a-day blog (and now pretty much a once-every-four-or-five days blog), I use an app that provides a random latitude and longitude that puts me somewhere in the continental United States (the lower 48).  I call this “landing.”

I keep track of the watersheds I land in, as well as the town or towns I land near.  I do some internet research to hopefully find something of interest about my landing location. 

To find out more about A Landing A Day (like who “Dan” is) please see “About Landing” above.  To check out some recent changes in how I do things, check out “About Landing (Revisited).”

Landing number 2378; A Landing A Day blog post number 812.

Dan:  Today’s lat/long (47o 45.462’N, 120o 27.285’W) puts me in Central Washington:

And this is a first!!!  What “first” would I be talking about, you might ask.  Well, my titular entity is visible on the above totally-zoomed out Street Atlas shot!  So I labeled it!

Anyway, let’s take a more local look:

Today’s landing (2378) is the one southwest of Lake Chelan.  Amazingly, the landing shown to the northeast of Lake Chelan is landing 2375, just three landings ago!  That’s my November 9th Methow and Pateros post – with no mention of Lake Chelan.

Here’s my local streams-only map:

You can see that I landed in the watershed of that fan-favorite, “Stream Perennial,” on to the Mad River (1st hit ever!); on to the Entiat River (1st hit ever!).  I’ll zoom back just a bit:

The Entitat discharges to the Columbia (175th hit). 

As is often the case, I was so far out in the boonies that I have no relevant Google Earth (GE) Street View shots of my landing.  The closest is to the east by the Columbia River, about 11 miles from my landing. 

As for Street View shots of my drainage, I likewise have to go all the way east to the Columbia to see where the Entiat River discharges:

Here’s the lovely view that the Orange Dude sees, looking up the Entiat:

And when he turns around, there’s the mighty Columbia:

So of course, I checked the numerous small towns in the vicinity of my landing.  Guess what?  They were all

As I checked out the town of Chelan, of course I noted that it was at the downstream end of Lake Chelan.  And then – what the heck – I Googled the lake.  So, it’s a very beautiful lake and all, but where’s the hook? 

Then I googled “Lake Chelan Geology.”  I saw that there was a You Tube video posted by a Central Washington University geology professor entitled, appropriately enough, “Lake Chelan Geology.”  Of course, I clicked.

After just a couple of minutes of viewing, I knew I had my hook.

I told my wife Jody (who, like me, is a geologist) that I landed near Lake Chelan, Washington.  She immediately perked up.  Lake Chelan??  Cheryl’s brother Darrel and sister-in-law Carol live there!!

Now wait a minute.  Cheryl, Darrel and Carol? 

But anyway, this isn’t just any Cheryl.  This is Cheryl, one of the “Feathers,” a group of Media PA women who went to school together.  The seven of them (alas, now only six) were good friends in Junior High & High school and referred to themselves as the Feathers – based on a pillow fight gone bad.

So Jody and Cheryl and Sooze and Kathy and Debbie and Sally and (sigh) Sue stayed in touch through all these years, periodically getting together, but emailing and calling each other on a regular basis.  The husbands/significant others joined the fun, and all 14 of us got together on numerous occasions.  Amazingly (and I mean truly amazingly), all 14 of us really got along and enjoyed each other’s company.

We gentleman were jealous of the moniker the women had, so we came up with one of our own.  Proudly, we’re the Peckers.

But of all the Feathers, Cheryl has a special place in my heart because she (of all the Feathers) is the only devoted A Landing A Day follower.  And Cheryl saw a similarity in how I view the world with how her brother Darrel views the world, so she turned him on to my blog.

I was well aware that Darrel lived in Washington and was very tuned into geology, particularly the wondrous story of the Glacial Lake Missoula floods.  I knew that he and Cheryl went on a geology field trip, visiting the scablands and the Dry Falls.

I had corresponded with Darrel just a little, and I do believe that at some point he told me he lived at Lake Chelan – which, of course, I promptly forgot.

Well, Darrel (and Cheryl) – this post is for you!

Back to Lake Chelan geology.  I listened to the entire hour and seven minutes of Nick Zentner’s lecture, and totally enjoyed it.  And I learned a lot, as well.  I therefore cordially invite you, my readers, to similarly partake of the good Doctor’s lecture.  At least give it a shot, and see if he hooks you like he hooked me.

But I’m a realist, and know that probably the majority of my readers are already thinking “No way I’m using up an hour of my life listening to a geology lecture.”

So what did I do?  I rewound the tape (yea, right), but this time, I was typing, pausing, typing, pausing, etc., preparing not Cliff Notes but Greg Notes.

So here’s the lecture.  The Greg Notes (for those who’d rather spend 10 minutes reading than an hour watching) follow below.

 

Nick’s premise:  You’re a Washington geologist and you have a geologically-oriented friend named Jerry from New Jersey.  Jerry calls out of the blue and says that he has one day to spend in the State of Washington and he wants to learn as much about Washington geology as possible.  Considering the great geologic diversity in Washington, that’s a tall order.  Where do you meet him?

Mt. Rainer; the Dry Falls; the west coast?  Nope.  Nick would take Jerry to Lake Chelan.  Here’s what’s at (or very near) the Lake:

  • Continental ice sheets
  • Alpine glaciers
  • Third-deepest lake in the U.S.
  • The Columbia River
  • Glacial Lake Chelan
  • Ice age floods
  • Basalts
  • “Exotic terrains” (having to do with bizarre west-coast plate tectonics)
  • Metamorphic Rocks
  • Granite Batholiths
  • The biggest earthquake ever recorded in Washington

Everything but an active volcano.  OK, so maybe Jerry’ll need a separate trip to Rainier.

Lake Chelan is 50 miles long, one mile wide.  Most long and narrow lakes are artificially formed by damming up a river.  Not Lake Chelan.

Here’s a GE shot of the long, narrow lake:

Note the Narrows.  That’s going to be part of our story in a bit.

There is a dam, built in the 20s, but it only raised the existing lake about 20 feet.  Not sure why they built the dam . . .

But this is the third deepest lake in the U.S.:

  1. Crater Lake – 1949’ deep
  2. Lake Tahoe – 1645’
  3. Lake Chelan – 1459’
  4. Lake Superior – 1332’
  5. Lake Pend Oreille – 1152’

If you guessed the glaciers made the lake, you’d be right. But the bottom of Lake Chelan is 386 feet below sea level!  How did the glaciers do that?

Other nearby glacial lakes are formed when alpine glaciers (glaciers formed in a particular valley and limited in extent to the valley) push up moraines that dam up the valley, creating a lake.  But these are much, much shallower.  For years, Nick didn’t think much about it; he just figured that the alpine glacier in the Chelan valley somehow dug a deeper hole.

But he had to think again.  It turns out that the Canadian Ice Sheet made its way down to Central Washington.  That’s the same ice sheet that was 3000’ feet thick in Seattle.  And the same ice sheet that created the Lake Missoula floods [discussed numerous times in this blog.]  The ice sheet was about 5000’ thick in the Chelan valley.

The massive ice sheet crawled over and around the North Cascade Mountains.  An arm of it passed over a low spot in the mountains to the north, and ground its way down the Chelan Valley.  Five thousand feet of ice is a lot of ice that can move a lot of rock.

But there’s more to the story.  There was another arm of the same ice sheet that actually flowed north up the Chelan Valley.  It came from the east before curling up the valley.  The northern arm made it down to the Narrows.  The southern arm made it up to the Narrows:

Remember – these two “arms” are connected to the vast Canadian Ice Sheet. 

For nerdy, curious geologists, this is a big deal.  And if one were to make the claim about two separate continental ice sheet arms coming in from different directions, one better have good evidence.  Well, good evidence there is.

So, both arms of the ice sheet left moraines and till deposits – the moraines are the earthen debris that the glacier pushed out to the edges the valley (actually, much like an alpine glacier), and the tills are what it left behind as the ice melted.  Of course, geologists have studied the moraines and tills from both ends of the valley, and guess what?  They are entirely different! 

The northern arm came from the Cascade Mountains to the north and west, and the rocks in the moraines and tills are typical of the rocks in the Cascades:  granites, lava rock and light basalt (andesites).

The southern arm came from the east and was “bearing different gifts.”  This ice had traveled through the dark flood basalts (“layer after layer of German Chocolate cake”) of eastern Washington, and low and behold, the till and moraines of the southern end of the lake are loaded with these dark basalts.

Any questions?  And this unique glacial set-up also set up some interesting hydrology.  There were times when the two arms retreated, leaving a lake in the valley between the two ice masses.  Fed by meltwater, this lake reached elevations as high as 700’ above current lake level!

As happens with ice dams holding back huge volumes of water, the dam will fail, and a massive flood results.  For Glacial Lake Chelan, the massive flood headed south, towards the Columbia River.  The water left coulee scablands similar to those left behind after the much-more-massive Glacial Lake Missoula flood.

Moving on to bedrock and exotic terrains . . .

The deepest part of the lake is just north of the Narrows.  Why?  Well, just north of the Narrows, the lake is underlain by schist, a metamorphic rock with lots of mica that is softer than other metamorphic rocks.  So, the bottom blade of the ice sheet bulldozer was able to dig much deeper in the schist than other areas.

Further uplake is a much harder metamorphic rock known as gneiss.  It’s a much gneisser rock than the sloppy schist to the south. [My terrible pun, not Nick’s.]  Because the gneiss is harder, the northern end of the lake is much shallower.

Down lake (south of the Narrows) is a highly unusual and much rarer rock known as migmatite (the formation is known as the Chelan Migmatite Complex).  So what’s migmatite? 

Nick says it’s like a “swirl” cone you can order at a soft ice cream joint – that’s when the chocolate and vanilla are swirled together on the cone.  But the migmatite is a swirl of metamorphic rock and igneous rock.  More about migmatite in a minute, but first a quick word about “exotic terrains.”

Head further down stream, there’s another schist, and then another gneiss.

The various schists and gneisses are pieces of what’s known as “exotic terrains:” pieces of crustal rocks that came from far away, and were plastered against the North American tectonic plate by crazily complex tectonic movements.

They could have come from as far south as Mexico!

How do we know this?  The various schists and gneisses are very different in terms of temperature and pressure required for their genesis.  They couldn’t have been neighbors when they formed – they must have formed in regions far from each other, and were brought together by tectonic movement.

So where does migmatite come from?  Well, imagine this.  We’re in a volcanic region.  Below the volcano is a huge pocket of liquid magma that is the source for the volcano.  Way below the magma chamber is the boundary between the crust and the mantle (the Mohorovic Discontinuity, or Moho).

So what’s going on in this zone between the magma chamber and the Moho?  This is the zone where magma from the mantle is migrating upward to the magma chamber beneath the volcano.  And this migrating magma intertwines with the crustal rock, creating the swirl of metamorphic rock (the crust) and the igneous rock (the magma).  Ergo, migmatite.  Oh yea – by the way – the migmatite was forming 18 miles below the surface of the earth – 165 million years ago.

Here’s a very interesting aside:  It just so happens that to the east and north of the Chelan Migmatite is a large body of granite (more-or-less adjacent to the migmatite).  The traditional view is that they represent different exotic terrains, or at least are separated by some sort of fault that makes them very separate.  But there’s an alternate theory that is just now being investigated:

As mentioned above, the volcano/migmatite system occurred 165 million years ago.  Let’s imagine that the whole system was uplifted and cooled and turned to solid rock (granite for the magma chamber, underlain by migmatite).  Tectonic forces keep on doing their work, and the whole shebang is uplifted even more, layed on its side and exposed at the surface.

And then, a geologist happens on some outcrops of migmatite adjacent to some outcrops of granite.  As I just mentioned, he figures that there’s some kind of fault, or the two rock types represent exotic terrains.  But what if the two geologic bodies are intimately connected?  What if the migmatite has always been associated with that very same magma chamber?  Pretty cool, eh?  Stay tuned – ongoing research will figure this out one way or the other.

And an important aside – the 165 million year old migmatite is much older than the schists and gneisses in the vicinity (they’re like 100 million years younger).  Since the schists and gneisses are part of exotic terrains, does this mean that the migmatite was formed right here in Washington?  Or is it possible that it, too is an exotic terrain?  Oh my.  All of the unanswered questions . . .

Let’s talk a little more about the schist that’s south of the valley.  It’s for sure an exotic terrain – it was originally sediment at the floor of a deep ocean, and was transported to the surface, near Entiat.  [See my local landing map!]

So how do you do that?  Here’s a more-or-less direct quote from Nick:  “You take stuff on the ocean and you convert it into rock (#1); then it is metamorphosed into schist – with high temperatures and pressures (#2); and then get it to interior Washington and oh – by the way – at a couple thousand feet above sea level (#3).  Good Lord!  There are stories to tell.”

Continuing the quote:  “I mentioned there’s also a gneiss south of the Chelan valley.  This was originally sediment – mostly sand – deposited in an oceanic trench – also interpreted as an exotic terrain.  Once again, we need to turn the sand into rock, we need to apply heat and pressure to turn it into a metamorphic rock, and then somehow, we need to get it here along the Columbia in central Washington.  Am I blowing your mind?  Have you heard about this exotic terrain stuff before?  Boy, if I get gutsy enough, I’ll do a bunch of lectures, but you’ve got to eat your Wheaties to put all of this stuff together!”

One more piece of bedrock information. There are a slew of 50-million year old dark basalt “feeder dikes.”  These are the cracks in the older rock that transported the German Chocolate Cake from the depths up to the flood basalts.  They’re the obvious dark stripes you can see in outcrops all over the place around here.

Moving right along to the 1872 earthquake – estimated magnitude 7.4 – that was long suspected to be centered somewhere in the Lake Chelan area.  This quake (the largest in Washington in recorded history) shook the entire Pacific Northwest, but until three years ago, the location of the epicenter was unknown.

There was a large landslide south of Chelan where a big hunk of a mountain broke off during the earthquake, and temporarily dammed up the Columbia River.  This landslide – and its connection to the 1872 earthquake – have long been suspected.  It has been presumed that the landslide occurred somewhere close to the epicenter, but as I said earlier, the location of the epicenter has not been known until recently.

A seismologist from the USGS, Brian Sherrod, has been working on understanding the 1872 earth for many years.  But finally, Sherrod used LIDAR technology to find the fault trace. 

Here’s what NOAA says about LIDAR:

LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure variable distances to the Earth. These light pulses—combined with other data recorded by the airborne system— generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.

So, Sherrod managed to find the money to perform a LIDAR survey over a wide area around Lake Chelan (that “magically removes all of the vegetation.”)  He painstakingly checked the terrain, looking for a telltale linear feature – a “fault scarp” that might have been caused by an earthquake.

A fault scarp is an abrupt change in slope, where one side moved vertically relatively to the other, creating a linear cliff.

Here are some examples of fault scarps (from wherever, not Washington):

And

But my favorite:

Anyway, Brian found an excellent candidate in Spencer Canyon:

Here’s a GE Panoramio shot looking south towards Spencer Canyon (by LongBachNguyen):

Here’s a screen shot from the lecture, with Nick pointing out the trace of the fault scarp in Spencer Canyon.  You’ll never guess, but “U” mean “up” and I’m not going to even tell you what “D” stands for:

Moving over to Google Earth, I think I can see a little of the scarp:

He also found evidence of a relatively fresh landslide (the lighter area on this GE shot):

The Seattle Times actually covered Sherrod’s work as a news story (by Sandi Doughton, Nov 2014):

The quake struck on the evening of Dec. 14, 1872, long before the first seismometer was installed in the Northwest.

The fact that chimneys cracked in Olympia, trees toppled in Puyallup and fissures split the ground south of Seattle led early observers to assume the quake was centered under Puget Sound.

But windows also shattered as far away as Victoria, B.C., and people were knocked off their feet at Snoqualmie Pass. The first analysis of newspaper reports from the time put the epicenter not far from Vancouver, B.C.

The most compelling eyewitness accounts, though, trickled in from east of the Cascades, in the sparsely populated hills near Wenatchee. Settlers and Native Americans reported a massive slide that briefly dammed the Columbia River. Some claimed geysers spouted from the ground and gushed for months. Throughout Washington and Oregon, strong aftershocks kept the populace on edge for more than a year.

Subsequent studies proposed epicenters in the North Cascades and near Lake Chelan. Estimates of the quake’s size have ranged from magnitude 6.5 to 7.5, which would make it one of the biggest in recorded state history.

“No matter how you define it, that’s a big earthquake,” said USGS researcher Brian Sherrod, who led the modern-day hunt for the quake’s source. “It was felt from Montana and British Columbia down into Oregon and Northern California.”

Beginning six years ago, Sherrod brought a new tool called LIDAR to bear on the puzzle. The technique allows scientists to virtually strip away vegetation and generate detailed topographic maps by beaming laser pulses from an airplane and analyzing the way the signals bounce back.

The area near Entiat was already a prime suspect as the source of the quake, based on eyewitness reports and recurring swarms of small quakes. The first LIDAR images didn’t show much, though, so the USGS commissioned another sweep in 2013.

“When I looked at those, it just popped out,” Sherrod said on a crisp morning in late October as he led a team of geologists down a fire-blackened hillside in the Okanogan-Wenatchee National Forest and into a small valley that drains into the Columbia River.

He pointed to a faint ridgeline a few feet high that snaked across the landscape like an oversized mole track. “That’s the scarp.”

A scarp is a scar created when an earthquake ruptures the ground surface. This one extends at least 3.5 miles, bearing witness to a major upheaval in the recent past, Sherrod said.

“Clearly we have a fault. There’s no doubt about it,” he said, scrambling into a 15-foot-long trench cut perpendicularly across the scarp. He named it the Spencer Canyon fault, after the drainage where it’s located.

The steep terrain and winding road ruled out the use of a backhoe, so Sherrod and his team dug two trenches by hand.

Here’s a picture of hydrogeologist Tanna DeRuyter helping to dig one of the trenches:

[Hey!  I’m a hydrogeologist!]

In the exposed dirt walls, Sherrod traced the diagonal line that marks the fault. Soil layers on one side are higher than on the other, he explained, revealing the way the ground jerked during past quakes.

Scraping the walls of the trenches and using colored pins to delineate layers, the geologists have uncovered evidence of at least two quakes, and perhaps as many as four.

But did the most recent one strike in 1872?

Moving to LiveScience.com 2015 article by Becky Oskin (about the results of the 2014 field work), the question was answered:

In one trench along the newly identified fault, Sherrod discovered a distinctive ash layer called the Mazama ash, blasted out by the volcanic eruption that created Oregon’s Crater Lake more than 7,000 years ago. The ash layer is now offset from itself about 6.5 feet on either side of the fault, Sherrod said.

In the second trench, the Spencer Canyon fault pushes 75-million-old gneiss (a metamorphic rock) on top of soil that has bits of charcoal just 285 years old.  [From a forest fire – and the charcoal can be accurately dated using carbon dating.  So the earthquake happened less than 285 years ago, or after 1730.]

The young charcoal helped link the fault to the 1872 earthquake by providing a maximum age for its recent movement.  Sherrod also showed the fault scarp is older than two small landslides that buried it. The oldest trees growing on top of the landslides are 130 years old, he said. [So the earthquake happened before 1885.]  Ponds created by the landslides also drowned trees, and those trees were killed sometime in the past 300 years.

“The evidence pins down the action to a window of time,” Sherrod said.  [And that window is between 1730 and 1885.]

A period of time consistent with the 1872 earthquake.

One could argue he hasn’t proven anything, but then again, there’s no evidence for any major earthquake during that time period besides the one in 1872 . . .

Back to Nick’s talk . . .

So, this is a shallow earthquake.  What’s going on?  Generally, western WA is moving to the NE, and Central Washington isn’t moving.  Something has to give, and what gives are fault blocks that are pushed up and out of the way as these tectonic plates inexorably keep moving, resulting in an extremely slow-motion collision.

Interesting side note.  While Nick is waxing poetic about some bedrock outcrops, he mentions that one is on the road to Pateros.  As mentioned early in this post, I featured Pateros just three landings ago, but without a word about Lake Chelan or the local geology.

OK.  Enough geology already.  It’s time to close out this post with a GE Panoramio shots, this one looking across the Columbia Valley near Spencer Canyon, by Jeffrey King:

That’ll do it . . .

KS

Greg

 

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