Wickersham's Conscience

High Island. It isn’t very high. Just 32 feet above sea level. It isn’t an island. It’s just a very modestly elevated part of the Bolivar Peninsula on the southeast Texas coast. It’s surrounded by oil wells. It’s a hurricane magnet. But High Island is also one of the best places in North America to see migratory birds, especially the small songbirds.

Two of the migratory corridors used by birds cross from the Yucatan Peninsula in southern Mexico across the Gulf of Mexico to the coast of southeast Texas.

Mississippi Migratory Corridor

Central Migratory Corridor

You can see that both routes make that big leap across the Gulf of Mexico, 16-24  hours of continuous flight for the birds involved, almost all of which cannot land on water.

You can also see that both routes send at least some species of birds all the way up to interior and even northwestern Alaska. But that comes later, first they have to survive and recover from the crossing of the Gulf of Mexico.

If you are a bird flying across the Gulf, the trees on High Island are the first bit of land you are likely to see, and if you are a bird that likes to perch in or around trees, you are going to fly directly to them. And because the trees on High Island are pretty much the only trees along the coast, by virtue of the “high” part of High Island, the destination is pretty well focused on the trees of High Island.

So High Island is a natural target for birds that are pretty well exhausted from 16-24 hours of continuous flying. They are tired, hungry and thirsty. A birder’s dream situation. Lots and lots of beautiful little birds that aren’t strongly inclined to be flighty, that pose nicely for photographers and that are much more concerned about food and water than funny big critters with binoculars.

Warblers, vireos, thrushes, tanagers, kinglets, swallows, martins and flycatchers; it’s a truly amazing spectacle.

High Island is a geologic and geographic accident. The extensive layers of salt 30,000 feet under eastern Texas escaped the layers of rock that usually seal them in and extruded a salt dome under the Texas coast. That salt dome – a mile-wide column of semi-plastic salt, actually – pushed up the upper limestone layers into a very modest hill. The angled layers of limestone around the edge turned into a petroleum trap.

The higher land escapes frequent flooding by ocean salt water, so the soils support the trees that are visible far out at sea and are so attractive to songbirds. It’s the highest coastal landform between the mouth of the Mississippi and southern Mexico, and it serves a lighthouse beacon for those migrating songbirds.

As a result of this geological accident, for eight weeks or so each spring High Island is an equally powerful beacon for North American birders. Mid-March to mid-May, and especially the second and third weeks of April, there are dozens of birders roaming High Island every day.

If the circumstances are just right, or just wrong from a migrating bird’s point of view, a cold front will bring winds out of the north. Those are head winds for the birds, and they arrive even more tired, exhausted, and a “fallout” of birds occurs. It’s paradise for a birder. Thousands of exhausted birds perched everywhere. It’s not so good for birds, and its something birders don’t hope to see. But it’s something a birder wouldn’t mind, you know, seeing just once.

But even in normal conditions, it’s a great place to bird. A Golden-winged Warbler, or a Worm-eating Warbler, for example, will attract a crowd.

Smith Oaks Birders, High Island, on a Hot Warbler - Photo by Mrs. WC

There’s even bleacher seats for the birders who want to hang out at a pond.

Bleacher Birders, Boy Scout Woods - Photo by Mrs. WC

WC enjoyed his brief visit to High Island immensely. Great fun, great birds and great company. And pretty cool geology, too. Serious props to the Houston Audubon Society, which has helped to preserve the remaining stands of trees on High Island, for the benefit of birds and birders, and manages the sanctuaries there.

WC is birding, a long ways from Fairbanks. There have been some challenges, but it’s going well. As proof, WC offers a few photos of birds that are not seen in Fairbanks.

Grey Catbird, Boy Scout Woods, High Island, Texas

The Grey Catbird is fairly common west of the Rocky Mountains. It’s best known for its call, which is very like a cat’s. This fellow was working up the nerve for a bath.

Scissor-tailed Flycatcher, Anahuac Nat'l Wildlife Refuge, Texas

This extravagantly-tailed flycatcher is found in the southern half of the midwest. Despite the ridiculously long tail, it’s nimble in the air and great at snagging bugs.

Acadian Flycatcher, Smith Oaks, High Island, Texas

The Empidonax genus of flycatchers is a birder’s nemesis, with half a dozen individual species that all look pretty much the same, including this Acadian Flycatcher. The olive back and the buffy eye ring help ID this handsome little bug vacuum.

Blue-winged Warbler, Boy Scout Woods, High Island, Texas

WC has saved the best for last, an especially handsome Blue-winged Warbler. The very low light required ISO 1600, which created a bit of noise. But the dramatic coloration shows pretty well.

Most of WC’s birding time right now is devoted to High Island, which isn’t very high and isn’t an island. It must be a Texan thing. WC will guess that a salt dome deformed the underlying limestone, pushing the circular area that’s High Island up about 12-15 feet. Not enough to save it from hurricanes. But it’s the first patch of land that birds migrating across the Gulf of Mexico see. So it’s a great place to be in spring migration.

To readers of a certain age, Big Bird, muppet and perennial star of Sesame Street, is an icon. Big Bird is also big, a free-standing puppet that is 8 feet 2 inches tall. But there’s a new Big Bird on the scene, a really big bird, or at least a proto-bird. Meet Yutyrannus huali, which means “beautiful feathered tyrant” in a combination of Latin and Mandarin.

Yutyrannus huali and Big Bird, to Scale - Original by Brian Choo, Big Bird added by WC

Fossils of this newly-discovered Lower Cretaceous/Late Jurassic dinosaur, a cousin to the later and famous T. Rex, was found in Liaoning Province in northeastern China. Plainly visible in the fossilized remains were impressions of feathers; this 30-foot long dinosaur has feathers. The feathers were simple filaments, like the fuzzy down of a modern baby chick and not the evolved, variable plumes of an adult bird, but plainly feathers.

Yutyrannus huali Tail Feathers, Xang Hailong

The original article in Nature (pay wall). What makes these discoveries remarkable are that these fossils are much older than the previous earliest known feather dinosaurs, they occur on animals 30-40 times larger than previously known, and they occur on adults, killing the theory is was insulation for dinosaur kids.

Dinosaur geeks will take WC to task for calling Y. huali a “proto-bird,” this is a different lineage than the family of dinosaurs believed to have evolved to birds. But you don’t have to be able to fly to be a bird; you need feathers and eggs. Q.E.D.

What was the purpose of the feathers? Sexual characteristic? Insulation? Something else? Feathers represent a significant energy investment, and the floor is open to speculation as to the evolutionary pressure that caused these big beasties to develop feathers.

It must be a very exciting time to be a dinosaur paleontologist. WC may lack the patience for  paleontology. But the recent discoveries are nothing short of amazing.

Dr. Kirk Johnson and Ray Troll at Gulliver's Books

Dr. Kirk Johnson and Ray Troll were at Gulliver’s Books in Fairbanks on Friday night, talking about their 2007 book Cruisin’ the Fossil Freeway, telling stories and autographing books. It was a hoot.

Johnson is a paleobotanist, a fossil-hunter who specializes in the fossils of plants. As he puts it, he goes time traveling with a shovel. He understands William Faulkner’s line, “The past is not dead. In fact, it is not even past.” He has a gift for telling stories, and is a science popularizer par excellence. Plus, he can find dinosaur footprints in roadcuts driving by at 65 mph.

That’s not the kind of skill you’d expect to find in the Vice President of the Denver Museum of Nature and Science, but it’s true. As well as a Ray Troll drawing.

Ray Troll is, well, he’s Ray Troll. He’s an Alaska treasure, a man comfortable with fish, evolution, puns, geology, the Amazon, puns and Truly Awful puns. His surrealistic art has anatomically correct critters. And he’s a fine public speaker, too. He gave a very nice, 45 minutes summary of the book and the adventures that led to it, complete with excellent KeyNote slides. He is, of course, a Mac user.

He can and did talk knowledgeably about the Morrison Formation, Pleiosaurs, Triceratops, Jackalopes, Ammonites and the strata of the Wind River Canyon. He can draw a vivid explanation of Natural Trap Cave – the mother lode of Holocene mammal skeletons – and make a joke at the same time: “Forty Thousand Mammals Can Be Wrong.” He sells t-shirts, but world class museums compete for his exhibitions.

Johnson wrote the book, mostly. Troll illustrated it. Johnson has a easy writing style that is comfortable explaining deep time, Troll’s penchant for cheeseburgers, the mechanisms by which fossils are made and preserved and the endless variety and availability of fossils.

Look Under Your Feet, © Ray Troll

The book is science blended with the road story of Troll’s and Johnson’s trip together and excursions into some of the pleasures of geology. A couple of WC’s heroes wander into the story, including Dr. David Love, the subject to John MacPhee’s superb Rising from the Plains [Amazon link], and how Love came to have a dinosaur named after himself. Or at least a dinosaur track; the late Cretaceous, four-toed species is known to science only from its tracks. And, as it turns out, Love once took Olaus and Marty Murie, of Alaska fame, fossil hunting. You never know what’s going to wash up when you beach comb the shores of science.

And the book is filled with amazing new characters, too. Like “Buck-a-Bug” Jimmy Corbett, who finds trilobite fossils and sells them to Fossil King Robert Harris for a dollar each. As Troll skillfully points out,  if we look under our feet, the past is all around us.

There are Christianists, religious zealots and various prigs who would deny us and our children our true heritage: billions of years of history, deep time, and tens of millions of species that were long gone before mammals even evolved. They’d force our public schools to deny the existence of The Dinosaur killer, the K-T boundary that is the dinosaurs’ epitaph and all that went before and since. Johnson was raised in the Seventh Day Adventist Church, and his story of the moment as a teenager he realized Noah’s Flood was not the default answer to every geologic problem could stand as an object lesson for all creationists.

Ray Troll was kind enough to sign a few of WC’s books, and both Troll and Johnson signed a copy of Fossil Freeway. They are fine souvenirs, and will have a place of honor on WC’s bookshelves. But the bigger take away from the evening is the hard, clever work of these two gentlemen who are working to tease a little knowledge of the past into the thick, stubborn brains of Americans.

WC is grateful for their efforts and wishes them every success.

However much humankind may injure and maim the planet, we don’t control nature. Nature bats last. WC introduces a new category of year end reviews, noting instances in this calendar year when we’ve had to be reminded of that lesson once again.

One of WC’s all-time favorite books is John McPhee’s The Control of Nature (Amazon link). McPhee examines three instances of man’s interactions with nature: the massive volcanic eruption at Vestmannaeyjar, near Iceland, and the efforts to protect the harbor there from advancing lava flows; the efforts by the U.S. Army Corps of Engineers to keep the Mississippi River from changing its course at the Atchafalaya Channel; and the City of Los Angeles’s efforts control the massive mudflows coming down out of the San Gabriel Mountains. McPhee’s message is that mankind may have short-term successes, but can’t win in the long haul. Nature bats last.

Each year, mankind gets a fresh set of reminders that for all out vaunted science, engineering and technology, we’re here at sufferance.

The list might both begin and end with the March 11 Tohoku ML9.0 earthquake and 40-foot high tsunami, which devastated northeastern Japan and wrecked the Fukushima nuclear power plant.   The tragedy has so far resulted in 15,842 deaths, 5,890 injured, and 3,485 people missing across eighteen prefectures, as well as over 125,000 buildings damaged or destroyed. Radiation contamination has resulted in a 20km exclusion zone, likely to last for decades. The engineering that went into the reactor and safety design was woefully inadequate for a foreseeable disaster.

The drought in the southwestern United States continued. From 2010-11, Texas experienced its driest August–July (12-month) period on record. Wildfires, crop failures and animal deaths are the worst since the Dust Bowl. Droughts also afflicted places as far flung as China, East Africa and Tuvalu, Micronesia. To some extent, they are probably the result of the extended La Niña in the Pacific Ocean, but the devastation, particularly in East Africa, is horrific.

In Joplin, Missouri. a devastating EF5 multiple-vortex tornado struck late in the afternoon of Sunday, May 22, 2011:

May 2011 Path of Tornado Through Joplin

There’s an estimated $3 billion in damage, and 161 people were killed.

Hurricane Irene caused 56 deaths and $7 billion in damages, with the worst of the damage from flooding in Vermont, which experienced its worst flooding in centuries. A fairly modest Category 1 hurricane when it came ashore in the northeast, it carried enough water and was moving slowly enough that it caused catastrophic problems. We think of hurricanes as a disaster afflicting the southeastern states; we’re wrong.

Earthquakes, particularly big quakes, are consequence of living on a geologically active planet. But there’s increasing evidence that some quakes are man-made, with fracking -– hydraulic fracturing for oil and gas – as a primary cause. The near-unprecedented weather extremes in 2011 – flood, drought, heat waves, tropical storms – may be the result of anthropogenic climate change. Warmer air carries more water, contains more energy and could generate more violent weather.

Death rates and property damage levels aren’t a particularly good analysis tool. There are more people and more improvements to land every year. But if you measure weather by the number of hurricanes, the energy level of hurricanes, the number of tornadoes and the intensity of tornadoes, then it does appear that nature is batting last.

Thomas Kuhn, 1922-1996

The single most often-cited book in scientific literature is the late Thomas Kuhn‘s The Structure of Scientific Revolutions. it certainly had an immense impact on WC, who had the chance to live through the kind of paradigm shift that Kuhn described while chasing a minor in geology in 1971. It may be that we are on the cusp of a similar paradigm shift in physics.

Kuhn posited “normal science” when research is focused on a broadly accepted theory or “paradigm.” A scientific revolution occurs when results become irreconcilable with the existing paradigm, resulting in a paradigm shift, a new paradigm and a new form of normal science. Kuhn argued persuasively that the linear progress of science was a myth. Most of science is a series of revolutions in thinking and understanding.

Copernicus and Galileo created a paradigm shift with heliocentricity, with the sun and not the earth as the center of things. Darwin’s work on evolution of species triggered a similar revolution in biology. Einsteinian physics replacing Newtonian physics. In WC’s own lifetime and experience, plate tectonics completely revolutionized geological thinking.

In physics we are seeing a predictive Kuhn pattern, increasing numbers of observations that cannot be reconciled with current theories of physics. WC can point to four obvious examples:

1. It turns out the overwhelming matter mass of the universe is compose of “dark matter,” stuff that exists but we cannot observe. It barely interacts with normal matter. Physics struggles to explain what the stuff might be.
2. The universe isn’t just expanding; the rate at which it is expanding is increasing. The fact is the most astonishing observation in science in decades. Scientists posit something called “dark energy” as the cause of the entirely unexpected acceleration, but haven’t a clue what it is or why it exists.
3. Twice now, physicists have observed elementary particles called neutrinos going faster than the speed of light. That’s impossible by the known rules of physics; the speed of light is universal speed limit.
4. The Higgs Boson, an obscure elementary particle whose existence and characteristics are predicted by physics, cannot be found, despite strenuous efforts to produce it.

Expressed as a pie chart, the size of the problems facing modern physics theories is evident:

Mass-Energy Pie

Modern physics understands and explains just 4% of what it can directly and indirectly observe. The remaining 96% is as opaque to science as its name suggests. When a scientific theory, what Kuhn called a “paradigm,” can no longer explain what is observed, we are ripe for a scientific revolution, for a paradigm shift. Physics would appear to be ripe for just such an event. Kuhn, WC thinks, would predict a coming paradigm shift in physics.

The last paradigm shift in physics gave us wonders and perils: everything from GPS technology to black holes to Hiroshima and Nagasaki. What wonders and perils would a new paradigm give to us?

When WC was just a pup, on his first trip through the Black Rapids Canyon,WC’s dad pulled the Travelall out at the Black Rapids Glacier Overlook. And the glacier was Right There! The ice face, admittedly a muddy mess, was close enough that WC could see rivulets of muddy water running down the snout. Great piles of gravel were pushed up in front, like God’s own bulldozer. It probably was further away than it seemed at the time, with the maximum surge years past, but the outflow stream was washing across the snout of the glacier, and was washing big chunks of ice into the Delta River right under the overlook.

That was a long time ago now. Now the glacier’s snout is buried under a mass of moraine, miles up the canyon, out of sight of the overlook. You need binoculars to see the patches of ice exposed in the lateral moraines. Trees grow where there was 500 feet of ice when WC was first there.

Glacial Ice Exposed by Slumping Lateral Moraines

This photo was taken June 2011 with a 600mm lens; the exposed ice is about 3-4 miles up the valley, on the north side. You can see by the height of the gravel above the exposed that the glacier was recently hundreds of feet think.

It was the surge of 1936-37 that gave Black Rapids Glacier its nickname and its fame. It even made Time Magazine. At one point, the glacier was surging at the rate of 30-65 meters a day across an ice face 1.5 miles wide. Since that surge, the glacier has steadily retreated to the current historic minimum.

Black Rapids Glacier Map (USGS)

But even its diminished form, its still the biggest glacier in the central Alaska Range, running from the Susitna Divide, where the Susitna Glacier starts, to the current snout, more than 40 km.

The Denali Fault lies under Black Rapids Glacier over the glacier’s entire length. The November 3, 2002 M7.9 earthquake shifted the north and south side of the Denali Fault by as much as 8 meters. It was the largest inland earthquake in North America in 150 years.The fierce shaking brought a number of huge rockslides down on top of the glacier.

Rock Slide over Black Rapids Glacier (USGS Photo)

The rock slide will have altered the mass balance of the upper glacier, and perhaps provide some insulation. But the net effect seems to be unknown.

Glaciers, like volcanoes and earthquakes, are geology in human time. Not all geologic processes are slow. Solid ground can shake; glaciers can gallop. We’re just along for the ride, whatever we may tell ourselves.

Book Review: Cascadia’s Fault, by Jerry Thompson (Counterpoint Press 2011)

The story Jerry Thompson has to tell is critically important, intriguing for anyone interested in science and as current as the 2011 earthquake and tsunami in northeast Japan. WC just wishes Thompson had told the story better.

While the San Andreas fault gets all the publicity, it’s not the most dangerous earthquake fault in America, or even on the west coast. That dubious honor goes to the Cascadia fault, where the easterly edge of the Juan de Fuca Plate is being stuffed under the northwest coast of North America. Extending from northern Vancouver Island to northern California, the plate is jammed. Locked up tight. At the rate of about 4mm a year, pressure is building. It doesn’t sound like much, but the last major quake was in 1700, and based upon field work measured ML8.7-9.0, about the same magnitude (and for about the same reasons) as the disastrous 2011 quake off northeastern Japan. Geologists estimate a 37% chance of a major ML 9 quake in the next 50 years. Such a quake and attendant tsunamis would be disastrous, if anything worse than those videos of what happened in Japan.

It has to do with Alaska, too. The tsunamis generated by the 1964 Prince William Sound quake – another megathrust event – did serious damage to the Pacific Northwest coast; the Cascadia fault, when it goes, will likely return the favor. Alaska will have more warning than most, but remains ill-prepared.

Thompson tells the story of how the new science of plate tectonics developed, and specifically how those developments helped create an understanding of the geology and the risk the Cascadia fault presents. It’s approximately what John McPhee did in Annals of the Former World (Amazon link), but focused on the Juan de Fuca Plate. And Thompson isn’t the writer that John McPhee is. Thompson very nearly makes an interesting story tedious.

Partly, WC thinks, that’s because Thompson is a newspaper reporter and the skills that develop a 1,000 word feature piece for a newspaper don’t lend themselves to a 342 page book. Partly it’s because Thompson feels compelled to say plate tectonics was a revolution without doing an especially good job of saying why. WC is a geology minor; WC was at the University of Oregon when some of the early research was going on. It was the most exciting time WC has had in a classroom, with professors fresh off research ships studying the geology of the area, telling us what they had found and inviting us to develop their ideas with them. We took field trips to the Oregon coast to study uplifted relic beaches. We visited the “ghost forest” of cedars. We dug muddy trenches in the Siuslaw River estuary.

All or almost all of that excitement is missing from Thompson’s book. WC does give him points for not being alarmist. There is indeed a terrible risk for which the Pacific Northwest is horribly underprepared. But this isn’t going to be the book that seizes the imagination of elected officials or the voters and gets them to start planning.

Three stars for the importance of the subject. It _should_ be read by everyone living in Oregon, Washington or B.C. that’s within 300 vertical feet of tidewater. But WC can’t blame them if they don’t make it through the book.

After the recent tragedy in Japan, perhaps non-geologists are a bit less inclined to regard the planet as static and unchanging. But other kinds of geology besides earthquakes and tsunamis happen on a human time scale. Glaciers are one example.

When George Vancouver explored Icy Strait in the northern end of the Alaska Panhandle in 1794, there was no Glacier Bay. There was a wall of ice two miles wide and 1,200 feet high where the entrance to the Bay is now. Today, the glaciers have retreated and it is more than 80 miles from the entrance to the snout of Grand Pacific Glacier. When WC was just a pup, the face of Black Rapids Glacier was washed by the Delta River; now the snout of Black Rapids Glacier is 10-11 miles back up the valley. Glaciers are geology in real time.

Hubbard Glacier and Vicinity

And then there is Hubbard Glacier, at the head of Yakutat Bay. A contrarian icefield, twice in recent years, in 1986 and 2002, Hubbard Glacier has surged and pressed up against Gilbert Point, sealing off the immense Russell Fjord. The many streams running into Russell Fjord backup, creating a glacier-made lake. If the ice dam created by Hubbard Glacier washes out before the water rises by about 40 meters, then Alaskans will just have a spectacle. The U.S. Geological Service has an amazing series of photos showing the 2002 glacier damming event. If a damming event lasts long enough to raise Lake Russell by 40 meters or more, then the water will exit via the Old Situk River channel, at the southeast end of Russell Fjord.

The consequences would be devastating for Alaska’s most productive steelhead trout fishery, an important salmon fishery and the village of Yakutat. What’s now a lovely clearwater stream and the linchpin of Yakutat’s economy, would become a partially saline, glacial river. The Yakutat Airport, near the mouth of the Situk River, would be jeopardized.

You can monitor the movement of Russell Fjord as it approaches and retreats from Gilbert Point. There’s been the usual, gradual spring advance, narrowing the distance by a hundred meters or so. Keep in mind that these are preliminary data, subject to review by the U.S.G.S.

Recent movement by Hubbard Glacier (preliminary data)

Glaciologists tell WC that it is only a matter of time before Hubbard Glacier seals Russell Fjord again. Everyone knows it. Everyone knows it cannot be stopped. And while it might be possible to create an alternate stream channel that would save tie Situk River fishery, there’s no political will to do so.

The loss of a world-class steelhead fishery that WC is very fond of it the least of it. But it is geology in real time.

Annals of the Former World, By John McPhee
Farrar, Straus and Giroux; (June 15, 2000)

John McPhee, in the opinion of most people, is America’s greatest living expository writer. In the opinion of the Pulitzer Committee in1999, this is his greatest work. Except, perhaps, for Coming Into the Country, it’s hard to argue with that conclusion.

McPhee set out to describe the geology across the United States, roughly along the route of Interstate 80. The decision came at about the same time as a revolution in geology, the emergence and dominance of the theory of “plate tectonics” and “continental drift.” The four books that comprise Annals, combined with the more recent essay, “Crossing the Craton,” were written across an interval of 15 years. The essays reflect the increasing maturity of those theories and the deepening understanding of the implications of that scientific revolution.

McPhee’s ability to explain complex geology concepts in everyday terms, and to humanize and de-mystify abstract science, has never been better. His ability to explain his topics through people, and to make those people come alive, has never been more skilled. In explaining the geology of California, for example, he notes that most of California, like most Californians, originally came from somewhere else. McPhee has not written primarily as science popularizer. But his writing here is so good, his explanations so clear and his understanding of the topic so profound that he shames most authors who work in the genre full time.

This is not “Rocks for Jocks,” as introduction to geology classes are often described. This is hard science, controversial theories and mind-boggling intervals of time laid out in terms that non-scientists can understand. From the creation of the Delaware Water Gap to the family history of geologist David Love to the details of the California gold rush, McPhee lays out geology and the consequences of geology in accessible ways.

Of course, this is all anathema to Creationists, who believe the world is only a few millennia old and deny earth’s rich, amazing past. That’s fine with WC. McPhee asks you to extend your arms out full length. If that’s the geologic history of our planet. A few passes of a fingernail file will wipe out the time man has been on the planet. If Creationists can’t cope with that fact, well, geology really doesn’t care.

It’s a brilliant book. After reading it, you’ll never look at a roadcut or the terrain around you in quite the same way again.

WC studied a lot of geology in undergraduate school. And he’s never quite shaken his interest in the area. Alaska’s geology is fascinating. To paraphrase John McPhee, most of Alaska, like most Alaskans, originally came from somewhere else. A case in point:

Up until a little less than 10,000 years ago, a very large lake covered much of eastern southcentral Alaska. The scope of the lake is still being researched, but it clearly extended north to Mentasta Pass, along the Tok Cutoff, east some distance up the Chitina River valley, and west to Tahetna Pass on the Glenn Highway. Recent geological data would have the lake look something like this:

Glacial History of Southcentral Alaska

Like most glacial lakes, Lake Ahtna was subject to catastrophic discharge events; the glaciers that dammed the rivers, creating the lake, would fail as dams, triggering massive flows of water down the lowest points around. There’s evidence of that kind of massive flood events down the Matanuska Valley into Cook Inlet, down the Tok River into the Tanana Valley and down Devil’s Canyon on the Susistna River. Some of these flood events may have involved 2,500 cubic kilometers of water. These were Lake Missoula-sized floods. At its largest. Lake Ahtna was much larger than present Lake Michigan; Ahtna may have had a peak water volume of 6,200 cubic kilometers; present Lake Michigan is estimated at 4,900 cubic kilometers.

The lake lasted perhaps 20,000 years, easily long enough to deposit vast amounts of mud on its lake bottom. When a flood discharge event occurred, lake bottom would become river bottom again, until the ice dams rebuilt as glaciers replaced what the high water had washed away.

As you drive down the Richardson Highway from just below Meiers Lake to Tiekel River, you are crossing the old lake bottom. The impressive Copper River canyon is eroded down through the lake bottom. If you look closely at the bluffs above the river, you can see the layers of lake bottom mud, graveled river bottom and, because this area is near the moderately active Wrangell volcanoes, the occasional layers of volcanic ash as well. This bluff is on the Edgerton Highway:

Depositional Layering, Copper River Bluff

This impressive pile also contains swamp mud, wind-blown glacial flour and less identifiable stuff.

The present-day Copper River has eroded down through these deposits, but you can see the old lake bottom still in the flatness of the terrain above the canyon.

Copper River Valley Erosion

As you drive down the Edgerton Highway, east off the Richardson, the road drops down a series of old lake terraces, marking old lake shores of a vast lake that is now long gone, but has left its geologic fingerprints all over the landscape of Southcentral Alaska.

It’s part of what makes geology so much fun. It’s a puzzle in which we live, often entirely unaware.