Rat Islands and Atomic Bombs

Amchitka is one of the Rat Islands--35-miles long and only 3-miles wide.  It is located near Kiska and very near the epicenters of those 1957 and 1986 earthquakes of magnitude 8.0 or larger.  The Google Earth image below shows the relative positions of Amchitka and Kiska, the two large islands in center of the image; the Aleutian Trench, part of which is called James Canyon along the bottom of the image; and Buldir Island, where the last remnant of the Aleutian Canada Goose population was found in 1962, in the upper left-hand corner of the image.  Of course, we now know that the very deep Aleutian Trench is actually there because the Pacific Plate is being subducted beneath the North American Plate, on which all these islands are located.  Can you see that when you look at James Canyon in the photo?  And, from the image, you can easily understand why so many of those earthquake epicenters shown along the Aleutians in the last post seem to be located just south of the islands.

Just before the Japanese abandoned Kiska in 1943, Amchitka became a major U.S. military base, but it closed after the war.  In the early 1960's, the U. S. Atomic Energy Commission created a nuclear testing facility on this island.  The WWII-vintage airfield and base camp were reused by crews preparing for underground nuclear tests. 

The first test was an 80-kiloton bomb known as "Long Shot," located 2,400 feet below the surface and detonated on October 29, 1965.  The second, "Milrow," was a one-megaton device located 4,000 feet below the surface and exploded on October 2, 1969.  The third, "Cannikin," was a 5-megaton bomb detonated 6,000 feet below ground level on November 6, 1971.  However, the morning before the Cannikin blast, the test site had hard rain and wind gusts up to 124 miles per hour.  Man may be able to destroy whole cities, but can't control Aleutian weather! 

Cannikin did come as close to being more powerful than nature than anything else man has ever built.  It was the largest underground nuclear explosion in U.S. history.  Some Alaskans, still rebuilding 7 years after the Good Friday Earthquake, were concerned that the explosion could trigger another “Big One.”  In fact, two days after the explosion, a crater more than a mile wide and 40 feet deep did form above the blast site.  But Cannikin generated no 1964-sized earthquakes on the mainland despite producing a shock wave registering magnitude 7.0.  And no Aleutian volcanoes immediately began erupting.

Although I had no role in these tests, I was working in the Denver office of the Engineering Geology Branch of the USGS during the last two tests.  Several other geologists and technicians in my branch were working on all three tests—interpreting post-blast geologic data from the 1965 test and pre-blast data for the second two.  Several of my co-workers also spent months each summer during 1968-1971 performing fieldwork for these tests.  They drilled into the rocks of the test sites to obtain a set of rock “cores” that could be used for geologic interpretation of the blast zone.  These cores and simultaneous geophysical tests were also used to locate faults on which movement might be triggered by the blasts.  But the topics that they most often talked about when they returned to Denver were the poorly-maintained, WWII-vintage “deuce-and-a-half” (2-1/2 ton) trucks they had to use on Amchitka, the difficulty of getting supplies and spare parts for the drill rigs, and—now here’s a surprise—that they had to work outside every day in horrible Aleutian weather!  Of course they couldn’t really talk about the tests themselves because they were classified.

The Amchitka nuclear test facility closed in 1994.  But a government clean-up of the residual radioactive, chemical, and other hazardous waste left on the island continued for years after that.  Today, the buildings, roads, and airfields are gone and Amchitka's World War II role is just a memory, although their sites can still be picked out on Google Earth.  And, apparently, a small plaque commemorating the Cannikin blast is the only reminder of the island’s role in the Cold War.  Well, that and the fact that the island is still off-limits to visitors.  Fortunately, I didn’t have a role in the Amchitka cleanup.

Next time: We are getting anxious to get on the road—only another week to go!  But first, a brief discussion of faults—not the “it’s your fault!” kind, but the geologic “break,” “fracture,” “slip” kind that sometimes generate earthquakes.  The San Andreas Fault in California may be the one we most often hear about because it is responsible for earthquakes in heavily populated Los Angeles and San Francisco.  This post will introduce you to the Fairweather Fault, which is similar to the San Andreas in the way it moves, but much longer and with the potential to generate even larger earthquakes! 

Crazy Foxes, Lousy Weather, Earthquakes, and Atomic Bombs!

Attu and Kiska--during World War II, the Japanese invaded North America at only those two locations.  And where are those strange-sounding places?  Well, not on any road that we can reach on our trip up the Alaska Highway, that’s for sure.  And not even by the Alaska Marine Highway Ferry System.  They are two of the 200 islands that make up the Aleutian Island chain.  Attu is located at the far western end of the chain, about 1,500 air miles from Anchorage and Kiska is located about 250 miles east of Attu.  Both islands are so far west that the International Date Line would lie to their east if the line hadn’t been bent far to the west around them.  So, instead of being on a different day than the rest of Alaska, the Aleutians are just in a different time zone—Aleutian time—one hour behind the rest of Alaska.  Even Unalaska-Dutch Harbor, the only Aleutian town of consequence, the only one on Alaska time, and the only one that can be reached by regularly scheduled ferries or commercial airlines, is still located 800 miles southwest of Anchorage and 1,000 miles east of Attu! 

The Aleutian Islands contain four island groups: the Fox, Andreanof, Rat, and Near Islands (“near” Russia, which named them).  Interestingly, despite these names, there are no native foxes or rats (in fact, no native land mammals at all nor any biting insects) on the Aleutians.  Perhaps the mosquitoes were all blown out to sea by the constant windstorms, known as “williwaws,” that frequent the islands.  When I landed on Shemya in 1992, the aircrew pointed to the wind gauge outside the airfield terminal.  Instead of a windsock, it was a driftwood log suspended by a logging chain from a long arm (driftwood because there are no trees in the Aleutians).  Their tongue-in-cheek warning was “If the log is at 45 degrees, stay on the plane!” 

To relate only one example of typical Aleutian weather, when our plane left Anchorage, it stopped at Adak Island to refuel.  That was not because it needed fuel to reach Shemya (which is 30 miles east of Attu), but because, if necessary, they had to be able to circle Shemya for 3 hours.  This was so the crew could await a diminishing of high crosswinds or a fog bank or find a hole in a 10,000-foot high cloud bank commonly shrouding the island.  If not successful at landing in that length of time, they still had to have enough fuel to get back to Adak. 

Weather in the Western Aleutians is much the same year round—wind, fog, wind, rain, wind, snow--with temperatures ranging from 11 to 60 degrees F through the year.  Annual total precipitation is only around 21 inches.  However, snow generally “falls” horizontally due to winds off the Bering Sea, instead of more normal vertical snowfall!  If you want to learn more about Aleutian weather and its effects on humans, read “The Thousand Mile War” (see the reading list in my profile).

Three mammal species were introduced to the Aleutians during the historic period.  Two rodents, roof rats and deer mice, were accidentally brought to the islands in ship cargo.  In the late 1800's, the native sea otters disappeared due to over-hunting for furs for export to China.  So, in order to stay in business, the fur trappers purposely introduced Arctic foxes, a different color on different islands to prevent crossbreeding, and the foxes soon became feral.  The Aleutian Canada goose was then thought to have become extinct due to foxes consuming both young birds and eggs.  However, a surviving population of the big birds was discovered on Buldir Island in 1962.  To protect the rare bird, the government eliminated the foxes.  Today they are present only on Shemya, where they have been allowed to stay as a way to deter birds from nesting and interfering with the operation of military aircraft. 

The foxes on Shemya are the blue color-phase of the Arctic Fox, but do not have a white coat in winter like their cousins in the high arctic.  The tattered looking coat that occurs when these foxes shed their winter pelt has given them the nickname “scruffy.”  They are completely unafraid of humans due to being land-locked with us on a 4-mile by 2-mile island for 70 years.  For the same reason, they are now so inbred that some are nearly blind, others walk with a peculiar sideways gait, and I seriously doubt many can still hunt due to being fed handouts by personnel assigned to the island.  When I got out of the truck that brought me from the Shemya airfield to the dormitory where I stayed, one of the scruffies walked up to me, lifted its leg, and peed on my shoe.  I guess he knew I was new “territory” and he was just marking me as his territory! 

But enough about the animals and weather; it’s on to the reasons that the geology of the Aleutians is important.  The Aleutian Islands are the tops of submerged volcanic mountains belonging to a range stretching more than 1200 miles into the Pacific Ocean from the Alaskan Peninsula.  This partially submerged continuation of the Alaska Range separates the North American Plate from the Pacific Plate.  At this plate boundary, the Pacific Plate is subducting beneath the NA Plate, creating the deep Aleutian Trench on the Pacific side of the islands.  Due to the heat generated by friction between the plates, the Aleutians contain more than 25 active volcanoes—13 over 5,000 feet high.  The USGS photo below shows Mt. Kanaga on Adak Island during a 1994 eruption.

Some of the largest earthquakes in the world occur in the Aleutians because they are located on a plate boundary, a subduction zone, and part of that Pacific “Ring of Fire” discussed in an earlier post.  A 1965 earthquake in the Western Aleutians had an 8.7 Richter Magnitude, 6^th greatest on record worldwide (the 1964 Good Friday Quake, centered in Prince William Sound, was a magnitude 9.2, 2^nd largest ever recorded).  The 1965 Aleutian event not only caused extensive ground shaking, but also produced a tsunami that measured 35 feet on Shemya Island.  The tectonic setting of Shemya in the western end of the Aleutian Islands results from an oblique-angle collision of the Pacific Plate and the North American Plate.  In 1975, Shemya experienced a 7.5 magnitude earthquake that actually did more damage to its military facilities than the larger one 10 years earlier.  In 1986, a magnitude 8.0 earthquake was centered near Kiska Island, in the same general area as an 8.6 magnitude quake in 1957.  Finally, on June 19 of last year, Shemya experienced a magnitude 6.0 earthquake, but no tsunami.  A U.S. Geological Survey map showing earthquake epicenters and magnitudes in the Aleutians can be viewed below.

The Air Force closed Eareckson Air Station on Shemya in 1995 and the Navy closed its 6,000-person naval base at Adak, also built during WWII, in 1997, several years after I was on both islands.  The military facilities remaining on Shemya are now operated by DoD contractors.  The base at Adak was completely deactivated, cleaned up, turned over to a native corporation, and resettled by several hundred Native Alaskans.  I worked on the cleanup of hazardous waste on both of those islands.  In 2010, the Coast Guard closed its station on Attu.  This last military presence in the Aleutians ended 68 years after the Japanese landed on that island.

Next time: I mentioned atomic bombs in the Aleutians, but spent too much time on weather and animals.  So, the next post will be about those bombs.

Are you driving through “terrain” or “terrane”?  If you are looking at a topographic map, the answer is “terrain.”  If you are looking at a geologic map of western BC, southwestern Yukon, or southern Alaska, the answer may well be “terrane.”  Confused yet?  “Terrain” is the “lay of the land”—e.g., hilly terrain, mountainous terrain, etc.—and generally refers to differences in elevation or “topographic relief.” 

“Terrane” is a more complicated geologic term for a specific area of land that contains rocks formed by a particular geologic process, as in a volcanic terrane or a limestone terrane.  However, since the acceptance of plate tectonic theory in geology 30 years ago, “terrane” has taken on a narrower definition of broken-off pieces of continental plates, island arcs, or even oceanic crust that have crashed into (called “accreting” by geologists) a drifting continental plate instead of being “subducted” beneath plate.  These terranes then become an “exotic” part of the plate.  Dr. David G. Howell of the U.S. Geological Survey (USGS) in Menlo Park, CA, a specialist in terrane analysis, compares the drifting of continents to the motion of geologic “bumper cars"!

The western edge of the North American (NA) Plate has accumulated many long, narrow, flattened-out exotic terranes, some as big as Japan, or even California, over the past 200 million years.  The figure below, from the USGS website http://pubs.usgs.gov/gip/dynamic/Pangaea.html, shows a few of those terranes.  But this is greatly simplified from the newest geologic terrane maps of the West Coast of BC and Alaska. 

Of interest during our Alaska Highway trip is a particular terrane that is still in the process of bumping into the NA Plate.  Although in a remote area not near any highway, the Yakutat Block terrane covers a large area—360 miles long and 120 miles wide.  It is located on the coast between Glacier Bay and Cordova.  This Block has been moving onto the NA Plate at a rate of about 2.5 inches per year, or 4 miles during the 100,000 years since it first contacted the NA Plate.  The Yakutat Block can be seen on the map above as the light-colored "submarine deposits" area on the west (left) side of the long fault attached to the east end of the "Aleutian Trench" (just left of the ". . llia" in "Wrangellia Terrane").

Based on the rock types and fossils found in parts of the Yakutat Block, it apparently broke off the NA Plate at about the location of Prince Rupert and moved 330 miles north along one fault system at the same time 540 miles of relative movement occurred between the Block and the Pacific Plate, making it 870 miles northwest of its starting point after only 25 million years.  So, the NA Plate is now in the process of readopting one of its own children!

Once we get on the road and reach Washington State, we will be driving north along and across several of these accreted terranes on our way through Kamloops and Prince George, then up the Cassiar Highway (I hope, since it is now closed due to flooding!).  So, in the way of a hint about future posts, the north-south trending Okanogan-Okanagan valley is one of those “exotic terranes.”

Next time: Like crazy foxes, lousy weather, earthquakes, and atomic bombs?  Then you would love the Aleutian Islands!

 
 

 

When you put marshmallows into a cup of hot cocoa, what   happens to them?  Even if you drop the marshmallows from some height above the cup, they float to the surface (after splashing cocoa—“hot chocolate” to some of you—on the countertop), don’t they?  They float because they are “lighter” than the hot, liquid cocoa.  For marshmallows, this is because they contain a large percentage of air.  A boat also floats in a lake because it contains a large volume of air (e.g., a solid concrete block sinks in water, while a hollow concrete canoe floats—college engineering students actually have contests and races to prove this). 

Now, what will happen if we melt some butter in the microwave and pour it into the cup of hot cocoa and marshmallows?  First, we just ruined a perfectly good cup of hot cocoa.  But second, the melted butter (sorry, melted heart-healthy Smart Balance in our case) also floats on the top of the hot cocoa and flows beneath the marshmallows.  If you don’t believe this works, try it for yourself.  But, be sure to clear it with your wife first as mine is pretty particular about what I do in “her” RV kitchen! 

If you have some Peeps left over from Easter, you could use them instead of marshmallows.  They’re made the same way and were just going to get thrown in the trash anyway because no one actually eats Peeps, do they?  And, besides, the yellow color would contrast nicely with the hot cocoa.  Come to think of it, I should have “borrowed” my grandsons’ Peeps for my experiment.  I could have saved those perfectly good marshmallows for our favorite afternoon snack—microwave s’mores. 

You are probably wondering how hot cocoa, marshmallows, and melted butter relate to the geology along the Alaska Highway.  These foods are acting just like the mantle, continental crust, and oceanic crust of our earth where the North American (continental) Plate is drifting westward over the Pacific (oceanic) Plate (see photo below).  The hot cocoa is the earth’s hot mantle, the source of the heat in our volcanoes and geysers and the energy driving the “convection cells” that move the earth’s plates around, separating them or crashing them into each other.  The lightweight marshmallows are the continental crust (continents and large islands of the earth) that floats on top of the mantle.  The melted butter is the oceanic crust that also floats on the hot cocoa, but flows under (“subducts”) when it meets a marshmallow (continent).

 What happens to our marshmallows if we leave them in the hot cocoa without letting it cool too much (or drinking it too fast)?  First, the bottom of the marshmallows starts getting soft and gooey, then will actually begin melting and dissolving into the cocoa, right?  As it melts, it gets smaller and smaller until it becomes a mini-marshmallow and then may dissolve completely.

Because the mantle is hot, the bottom of the continental crust also heats up and begins melting.  If the melting continental crust finds a deep crack to flow through and is able to reach the surface, we may see an explosive eruption of light-colored “rhyolitic” (gooey and sticky like melted marshmallow) ash and lava.  A good example would be the explosive 1991 eruption of Mt. Pinatubo on the big Philippine island of Luzon (photo from: http://pubs.usgs.gov/fs/1997/fs113-97/ ).  Three days after this USGS ash cloud photo was taken, the volcano exploded in the second largest eruption on earth in the 20th century.

If melted oceanic crust travels through a crack to the surface, we may see a red-hot, semi-liquid, slow-flowing “basaltic” river of lava (kitchen analogy: molasses), as at Kilauea on the Big Island of Hawaii. 

Why do continents drift ("float") on the mantle?   You have all seen the periodic table of elements sometime in your past. Remember that some elements, like hydrogen, are much lighter (have a lower atomic weight) than other elements, like lead.   That's why we put hydrogen in balloons to make them float in air (air=78% nitrogen + 21% oxygen).   And why, pre-EPA, we used lead weights to sink fishhooks in our favorite fishing hole (and why a "Lead" Zeppelin is a flying impossibility, even filled with hydrogen!).

Rocks that primarily contain lower atomic-weight elelments like silicon (At. Wt.=28), aluminum (27), magnesium (24), and carbon (12) will be "lighter" than rocks containing higher atomic-weight elements like iron (56), manganese (55), and titanium (53).   Although iron is found in most rocks (that's why many are "rust-colored" in hues of orange, red, and maroon), the oceanic crust and mantle are very iron-rich and the continental crust is much more silicon-rich.  

If it helps to visualize this, find a clean plastic dish small enough to weigh on your kitchen scale.  If your wife makes her own jewelry, fill the dish with as many small glass beads as you can get in it, level with the top, and weigh it (don't break the scale!).  Now, do the same thing with as many very small finishing nails or tacks as you can pack/shake in, level with the top of the dish and weigh it.  If you packed the nails in tightly enough, the weight of the dish of nails should be much greater than the weight of the dish of beads. 

Now why did we just do this?  Because glass is almost pure silicon and small nails are nearly pure iron, so the iron should weigh more than the silicon, right?  Atomic weight 56 = 2 x atomic weight 28 or nails are twice as heavy as glass beads (if the amount of air is the same in both dishes!).  So, silica-rich continental crust (marshmallow) floats on the iron-rich mantle (hot cocoa) and rides over ("subducts") the slightly less iron-rich oceanic crust (melted butter).

Next time: Is it "terrain" or "terrane"?  Which are we seeing in Canada and Alaska?  The short answer is "both" but I'll discuss the very significant difference next.

Want to see more photos of Mt. McKinley glaciers?  I forgot to define a few terms relating to mountain and tidewater glaciers a couple of posts back.  So, this post will attempt to rectify that omission.

Tarns are small lakes that fill cirques, the circular snow accumulation bowls on mountain slopes.  An arête is a sharp ridge of rock that is left between two cirques that are being eroded toward each other.  Arêtes may be seen on many peaks along the Icefields Parkway in Banff and Jasper NP and on the slopes of Mt. McKinley and other mountains in the Alaska Range.  My first 2000 photo below shows a classic bowl-shaped cirque on Mt. McKinley surrounded on three sides by arêtes.  The second photo, taken from slightly above the ridge, shows how just narrow and steep one of Mt. McKinley’s arêtes can become.  The photo also clearly shows the fracture (“joint”) pattern of the very hard, erosion-resistant granite that forms Mt. McKinley.

 

 

A horn is a sharp-pointed, pyramidal mountain peak formed by the“headward erosion” of several cirques. The Matterhorn in Switzerland is the most obvious and most famous example.  But my wife’s 2007 photo of cloud-shrouded Mount Saint Nicolas in Glacier NP, Montana is also a great example, with four cirques, one even containing a tarn, surrounding its peak and creating its classic pyramid shape.

 

I mentioned earlier that glaciers are very effective bulldozers and can excavate large volumes of rock as they move.  When a glacier flows down a “V”-shaped mountain valley originally formed by stream erosion over many thousands, or even millions of years, it can quickly widen and deepen it into a classic “U”-shaped glacial valley, sometimes in only a few hundred to thousand years.  This gouging out of rock by ice is exactly like using a piece of coarse sandpaper on a newly cut 2x4.  The sandpaper quickly smoothes the end of the lumber, but, due to the coarseness of its grit, it may also knock splinters off the corners.  And, just like coarse sandpaper produces large quantities of sawdust, the glacier produces huge volumes of “rock dust” (actually called “rock flour,” but known to geologists as “silt”).

The glacier picks up everything from sand to boulders and carries them along, frozen into the bottom ice.  The sand and gravel may smooth and polish or groove ("striate") the bedrock surface over which the glacier is flowing, but the boulders may knock off huge chunks where they hit an ice-wedged fracture (joint).  The glacier can also erode by “ice plucking,” where water freezes in those joints and, over time, loosens the rock sufficiently that it can fall onto, or is picked up by, the glacier.

What happens to all that rock debris that the glacier creates, incorporates into its ice, or pushes ahead as it moves downslope?  That debris is partly carried along by the ice and partly carried away from the ice by glacial meltwater streams.  The part carried by the ice is a random mix of every size rock particle.  The part carried by the streams is “sorted” by the running water (just like a sluice box sorts out placer gold from sand).  First, the boulders are likely not moved much by the water, the cobbles are dropped out a short distance downstream from the toe of the glacier, and the sand is carried greater distances downstream. 

Obviously, a tidewater glacier can drop all these particle sizes directly into the ocean.  But, in a mountain glacier terminating some distance from the coast, only the very fine “rock flour” may reach tidewater.  Because this silt-sized sediment is so fine and so easily agitated by waves and currents, it may take years to completely settle out, so may move far out to sea.  My 2000 photo below shows a tan-colored “rock flour” plume being discharged into the deep green water of the Lynn Canal near Haines.  The plume is coming from the Katzehin River, which originates as meltwater from Meade Glacier.  This glacier is actually located east of the Lynn Canal in the Coast Range, about 25 miles southeast of Skagway along the Alaska-British Columbia border.

 

This same rock flour/silt is found in Lake Louise and Moraine Lake in Banff NP and at many glacier-fed lakes like Portage in Alaska.  In those lakes, however, the water is a turquoise blue that attracts every photographer who sees it on a sunny day.  My photo is probably unusual in that regard, as few photographers are attracted to "dirty water," even if they know the cause!

Next time: How do plate tectonics and continental drift really work?  A kitchen experiment involving hot cocoa (hot chocolate), marshmallows, and melted butter provides an analogy that is easy to understand, but difficult to swallow! 

Imagine ice two miles thick covering your town!  If you are from the Great Lakes region, the Dakotas, Montana, Idaho, Washington, or most of Canada, that may well have been true of your region during the Pleistocene ice ages.  During the past 2-2.5 million years, perhaps as many as 10 distinct ice ages have occurred.  But each ice age didn’t last 1/10 of that time because there were warmer “interglacial” periods between each glacial advance.  Why are these ice ages important in understanding the geology along the Alaska Highway and its approaches?  Because nearly all the landforms you are seeing along your route—mountains, hills, river valleys, lakes, waterfalls, fjords, sand dunes, remaining glaciers—were modified by, or actually created by, this ice, its melt-water, or its winds.

During the Pleistocene, so much of the earth’s water accumulated in the thick “ice sheets” as snow and ice that sea level around the entire globe was as much as 450 feet lower than it is today.  This lower ocean exposed the Bering Sea “land bridge” that connected North America to Siberia and the remainder of the Eurasian continental land mass.  Also, at the times of peak glaciation, only the highest peaks in the Canadian Rockies were exposed above the ice.  This thick ice had a bulldozing effect many times greater than any glacial erosion that we see from mountain glaciers today.  So, even the hard bedrock of the Rockies shows the erosive effects all this ice.

Lobes of the ice sheets dammed up huge rivers like the Columbia, creating gigantic lakes, with names like Glacial Lake Missoula and Glacial Lake Columbia.  When these ice dams broke, as they did multiple times, the resulting floods (“jokulhlaups”—Icelandic, not Swiss!) gouged out great valleys (e.g., Grand Coulee) and stripped the soil and loose rock off the lava flows of eastern Washington (the “channeled scablands”).  In addition, the constant cold winds coming off these miles-high sheets of ice picked up sand and silt from the outwash plains at their edges, creating sand dunes, as at Carcross, YT, and in the Kobuk Valley National Park, AK, and windblown silt/rock flour-covered (“loess”) hills, like the Palouse of eastern Washington.

Features created directly by the ice include moraines and till (discussed in the previous post), drumlins, eskers, kettles, kames, tarns, arêtes, and horns.  Drumlins are rounded hills of till smoothed by the passing ice, with a steeper slope in the direction of movement.  Eskers are long, narrow, snake-shaped ridges of gravel that were formed by water flowing beneath the ice of a glacier or ice sheet. 

Kettles are small, generally circular lakes or ponds created when a chunk of gravel-covered glacial ice, left behind by a retreating glacier, melts and the surface collapses.  When I was investigating a proposed damsite in Devil’s Canyon on the Susitna River, our helicopter flew daily over hundreds of kettle ponds located between the Denali Highway and Devil’s Canyon.  These ponds contained huge numbers of grayling, but most had probably never been fished because the ponds were too small to land a float plane.  In my 2000 aerial photo below, the kettle ponds are clearly visible in the outwash plain below Ruth Glacier. 

Kettle ponds are often associated with kames, which are holes in the glacier filled with gravel by streams flowing across the surface of the ice.  When the glacier retreats, the gravel is left as a small hill. 

Also visible in the photo to the left are the areas bare of trees.  These grassy areas are not due to clear-cutting by loggers (they are all down in the Alaska Panhandle, not in Denali National Park).  They are the result of an extremely high water-table combined with one last feature left from the ice ages that no Alaska RVer will soon forget—permafrost.  Permafrost is just short-hand for “permanently frozen ground” (does anyone remember how to take short-hand?).  Soil that was frozen during the last ice age has, in Northern Canada, Alaska, and parts of the Rocky Mountains, never thawed out.  This frozen soil, on which only a thin surface layer thaws each year, creates the roller-coaster frost heaves that are the bane of RVers throughout the Yukon and Alaska.  All those little red or yellow flags that you soon come to love to see, but hate driving past, are due to glacial geology!

I don't know if it still exists in Fairbanks, but in the early1970's, I visited a "permafrost tunnel" operated by the University of Alaska and the U.S. Army Cold Regions Research Laboratory.  After we passed through an airlock designed to prevent thawing, we walked into a tunnel excavated in frozen Pleistocene gravel, sand, and silt.  Being an engineer, I felt very strange walking under boulders the size of a small car hanging in the ceiling with no visible means of support.  There were also interestingly shaped, dark-colored ice lenses in the walls and ceiling.  It was a tour I'll never forget, so not everything about permafrost is bad!

Next time: Tarns, arêtes, and horns should have been discussed in the last post because they are related to mountain glaciers, not ice sheets.  So, they will be discussed in the next post.

A Glacial Primer

Regardless of the route you use to get to Alaska   and to circle through the central part of that state, you cannot miss seeing glaciers.  There are glaciers in Banff and Jasper NP in Alberta; near Stewart-Hyder in BC; around Juneau, Haines, and Skagway for those traveling on the AMH ferries, along the Glenn Highway; near Valdez, Portage, and Seward; in Glacier Bay, Kenai Fjords, and College Fjord; and on the slopes of Mt. McKinley.  There are many types of glaciers, but the named glaciers along your routes are generally either "mountain glaciers" or "tidewater glaciers." 

Both mountain glaciers and tidewater glaciers may be tongues of larger, mountaintop glaciers called "icefields."  The large icefield that feeds the famed Athabasca Glacier in Jasper National Park is called the Columbia Icefield.  The icefield that feeds the Exit mountain glacier at Seward and the tidewater glaciers of Kenai Fjords National Park is called the Harding Icefield, named for the 1920's U.S. President who died of a heart attack on the way home from his only trip to Alaska.

Mountain glaciers consist of many parts, most of them originally named by the Swiss and some of which are shown in my 2000 photo taken from the air of Ruth Glacier.  Ruth Glacier is located on the southern flank of Mt. McKinley in Denali National Park.  A "cirque" is a bowl-shaped snow accumulation area that can be a source of snow and ice for a mountain glacier.  Because all glaciers act as very efficient rock excavators, they break rocks off valley walls as they move downslope.  This rock is called a "lateral (ie., side) moraine."  The rocks being bulldozed off the bottom of the glacial valley, pushed ahead of the toe, and left there when it begins to retreat are called a "terminal moraine."  And, when two glaciers flowing down adjacent valleys meet and join, their adjacent lateral morains also join forming a "medial moraine."  A "hanging glacier" is a steep wall of ice flowing out of a cirque or hanging valley, just like Yosemite Falls flows out of a hanging valley located above the U-shaped, glaciated Yosemite Valley.

If large quantities of rock fall from the cliffs of an oversteepened, U-shaped glacial valley onto the surface of a glacier and the glacier begins to retreat, the glacier can become completely covered by the rock debris. This is sometimes called an "ice-cored moraine" because it looks like a moraine even though it is actually still a moving glacier. The lower parts of Dome Glacier in Jasper National Park and Ruth Glacier in Denali National Park are ice-cored moraines.  My 2000 photo of Ruth Glacier on the right clearly shows both lateral moraines, the medial moraine, the ice-cored moraine, and an amazingly cloudless Mt. McKinley.

Remember, a mountain glacier is just a river of ice instead of a river of water and moves downslope by gravity flow just like a river of water moves downstream.   Therefore, "right" and "left" on a glacier are just as they are on a river--the right bank/lateral moraine is to your right if you are looking downstream or toward the "toe" (as opposed to "head") of a glacier.

Finally, the random mix of silt ("rock flour"), sand, gravel, pebbles, cobbles, and boulders dropped by a glacier when it melts ("retreats") is called "till."  And the better-sorted rock flour, sand, and gravel moved downstream by streams of glacial meltwater gushing from the toe of the glacier are called "glacial outwash," as shown in my photo of the meandering meltwater streams and glacial outwash plain below the toe of Ruth Glacier.

Next time: A little about some slightly larger glaciers--ones that covered most of Canada and much of the U.S., reached depths that left only the highest peaks of the Canadian Rockies exposed above the ice, and disappeared only 14,000 years ago.