The Enterprise — Michael Nardacci

Damoiselles: A pair of sunglasses shows the size of the tiny structures near the entrance to a Clarksville area cave. Pebbles in the clay matrix have protected the sediments beneath them, forming little columns.


A point I have always tried to make with my students or participants in one of my field trips is that geologists have a name for absolutely every natural process involving the rocky sphere that is Planet Earth.  And one of the wonderful things that has happened in recent decades is that scientists have sent robot probes to examine the surfaces of other planets, as well as asteroids and comets, and have found not only that many of the same processes occur on worlds as alien as the Moon, Venus, and Mars, but have discovered exciting evidence of other geologic phenomena unknown on Earth and waiting to be explained.

Over the past few days, the Internet has been sizzling with reactions to a rock photographed by the Curiosity Rover that has a passing resemblance to a thighbone.  Given the fact that not one of the robots sent there has yet found persuasive evidence that anything as large as a microbe ever lived on Mars, the curiously shaped rock is unlikely to be anything but that:  a curiously shaped rock.

But the various chat rooms that dwell on such things are buzzing with charges that NASA (the National Aeronautics and Space Administration) is once again concealing evidence of macrobiotic life on Mars and those who disagree are denounced in vitriolic (and often hilariously ungrammatical) language.

Yet the fact is that the natural processes which change the shape of Earth’s surface are sometimes capable of producing very curious results:  hence, the chess-piece shapes of the rocky towers of Bryce Canyon, the elegantly sculptured mesas and buttes of Monument Valley, and the granite profile of New Hampshire’s Old Man of the Mountains that collapsed ignominiously some years ago into a heap of rubble due to frost-wedging.

A few weeks back, on emerging from a trip with some students through one of the caves near the village of Clarksville, I noticed some odd, miniscule features on a pile of muddy debris at the cave’s entrance.  The debris was glacial drift, deposited on the Clarksville area by one of the streams pouring off the melting Ice Age glaciers thousands of years ago: hundreds of penny-sized and smaller pebbles in a matrix of packed clay.

But many of the pebbles stood atop a small, thin column of that clay, forming tiny structures geologists call by the French term “damoiselles”— which loosely translates as “little maidens.” Evidently, to the French-speaking geologists who coined the name, the pebbles resembled broad bonnets perched atop the slender structures below.

This happens when rain water or melting snow cascades down an exposure of soft sediment, washing away anything that is not protected by the tiny pebbles; their weight has slightly compressed and hardened the materials on which they sit.

In many places in the world, these structures appear on a much larger scale.  Chimney Bluffs State Park on Lake Ontario features enormous examples, which are often given the name “hoodoos” when they form such massive structures.  A somewhat smaller display of hoodoos appears on the mysteriously named “Ghost Fire Bend” of the Normanskill, though these are currently not accessible by car with the closing of Grant Hill Road due to road work.

In June of this year, while on a hiking trip to New Mexico, I had the opportunity to visit Tent Rocks State Park on the reservation of the Cochiti Pueblo, southwest of Santa Fe.  The preserve was originally given the Keresan language name Kasha-Katuwe, which is usually translated as “rocks that resemble teepees.” 

Here, between 6 million and 7 million years ago, the land was buried under the debris from an incredibly violent volcanic eruption that formed the Jemez Caldera, a giant bowl-shaped depression to the north.  Layers of the soft, spongy-looking rock known as pumice, compacted rock fragments called tuff, and volcanic ash buried the region in layers hundreds of feet thick.

The weight of all of that air-borne sediment compacted the strata into a crumbly matrix rock that weathers easily due to the wildly varying seasonal temperatures and is poorly resistant to erosion by the occasional rainfall or melting snow.  But mixed in with the smaller rock fragments are boulders, some the size of an automobile, and these had the effect of compressing and compacting the sediments that lay beneath them. Thus the sediments were protected from the raging, highly erosive waters that flow during those occasional periods in arid climates when sudden torrential rains fall.

The results are the hoodoos of Kasha-Katuwe, and they are marvels to behold.

Those found near the parking area for the preserve’s trailheads gave Tent Rocks its name. There are a dozen or more of them, ranging in height from a couple of yards to 20 or 30 feet, but these represent the last stage in the erosion cycle of the hoodoos.  They have lost their protective boulder caps and, in respect to geologic time, they are not long for this world.

Though this part of the Southwest is currently experiencing a severe decade-long drought, every drop of rain that does fall is washing them down to ground level, the eventual fate of all hoodoos.

To get a better idea of nature’s inventive sculpting talents, one must hike up one of the two major trails that head into the park.  They are easy for the experienced hiker, though the lack of shade and the unforgiving summer sun make it mandatory to carry a couple of quarts of water.  In addition, signs warn of poisonous snakes lurking in the underbrush — sufficient cause for those inclined to bushwhack to stay on trail.

A textbook example of the formation of the hoodoos lies on the edge of the eroding mesa around which the trail meanders.  Rising some 20 feet from the middle of a dry wash, the structure is crowned by a large boulder of pumice.

Farther along the trail, the hoodoos become larger and more varied in shape and one particularly steep slope offers a view of their entire life cycle:  some eroded down to mere stubs, some proudly displaying their protective caps, and others just beginning to emerge from the eroding cliffs.

They derive their weird shapes from the varying hardness of the rock strata from that they form. A slot canyon cut into the rock by raging waters offers a shady respite from the heat and climaxes in a hair-raisingly steep and exposed series of switchbacks leading to a jaw-dropping view out over the canyon to Sandia Mountain above Albuquerque.

The American Southwest — particularly in New Mexico and Arizona — features some spectacular geology due to its diverse rock types; its wildly varying elevations; and its climate, which tends to be arid but is subject to sudden intense flooding.

Terms such as “weathering,” “erosion,” “resistance,” “strata,”  “frost wedging,” and other prosaic expressions may seem lifeless on the page of the textbook.  But, in an environment such as Tent Rocks State Park, these dry words describe nature’s endlessly varied talent to create wonders in the rock from which Earth is made.


— Photo from Mike Nardacci

A field of glacial erratic boulders lies on a mountain west of the Great Sacandaga Lake.

Acadia National Park on Maine’s “Down East Coast” is a place of mystical wonders:  sheer granite cliffs rising from the sea, washed in the salt spray of enormous waves crashing against them; barren mountain peaks that seem much loftier than they really are, climbing upward from sea level and splashed with the colors of flowers normally found hundreds of miles farther north; spectacular stone bridges in the most unlikely places in the Acadian forests, gifted by John D. Rockefeller and looking like leftover sets from The Lord of the Rings films;  and miles of fir and hemlock coastal forests, the dark green boughs hanging with the lichen called Old Man’s Beard, wreathed in fog and dripping in a silence broken only by the haunting cries of gulls and the clanging of buoys.

But Acadia is also an enormous outdoor natural history classroom, and educational institutions such as the College of the Atlantic in Bar Harbor frequently use its features for courses in geology, marine biology, botany, and environmental chemistry, among others.

The mountains of Acadia and other even higher summits in interior Maine must have been among the last places in the northeastern United States to have had glacial ice when the vast Wisconsinan glacier — the most recent continental glacier — retreated as Earth warmed over the last 15,000 years.  U-shaped valleys, the odd asymmetrical mountains called “roches moutonnees” (which translates as something like “sleeping sheep”), bedrock showing the striations (scratches) caused by the advance of the glacier, and immense deposits of glacier-borne rock material all testify to the recent — in geologic time — Ice Age.

Glaciers are immensely powerful agents of erosion, and much of the upper part of the continental United States is covered in the debris they left behind.

The poet Robert Frost wrote frequently of the hardship of being a New England farmer — not the least of whose problems was the immense quantity of rock left behind in the landscape presenting an appalling challenge to the horse-drawn plough. His poem “Mending Wall” deals with the boulders — “some like loaves and some…nearly balls” that are ubiquitous in fields and which farmers for generations have used for stone walls and house foundations and churches.

The beaches of the Acadian Coast are famous for the almost infinite variety of types and colors of rocks found on them, many of which may have been transported for hundreds of miles from their point of origin: For it is a rule of glacial geology that an advancing glacier acts as a bulldozer, scraping away loose sediment and vegetation right down to the bedrock and then proceeding to abrade it, too, away;  but a melting or evaporating glacier acts as a dump truck, leaving behind all sizes of rock particles from tiny clay and silt to huge cobbles and boulders in one heterogeneous mess called glacial drift.

The larger particles — the cobbles and boulders — are known by the quaint name glacial erratics. The high summits and slopes of Acadia are dotted with thousands of erratics, and on many of the peaks such as Cadillac Mountain, the highest mountain on the East Coast of the country, they sit in rugged isolation, often looking like the remnants of the mysterious rocky circles found in Ireland and England.

One of them is a famous landmark for visitors to Acadia: It is called Bubble Rock and it perches picturesquely on the steep slope of the summit of a small mountain known as South Bubble.  It is an enormous chunk of the Lucerne Granite, a beautiful black-and-white speckled stone with large crystals that forms the bedrock some 40 miles north of Mount Desert Island

The sight of it challenges credibility: The slope appears to exceed the physicist’s “angle of repose” and it looks as if the slightest touch would send it careening noisily into the valley below it, smashing rocks and trees as it went.

Many visitors to Acadia National Park have appeared in the apparently obligatory photograph in which they attempt to dislodge it.  Legend has it that, on a Halloween night some years ago, the entire football team of a local high school hiked up and attempted to push it off South Bubble. But there it stands.

A charming children’s book (now, alas, out of print) attributed the precarious position of the rock to Acadian trolls.  But it must be remembered that on what is now the coast of Maine, the continental ice sheet was greater than a mile in thickness and thus had immense power to transport rocky materials: Retreating, it left this erratic and many others behind, sometimes in the most unlikely of locations.

Our own Helderberg hills and the Adirondacks also feature vast numbers of erratic cobbles and boulders, but, given the thickness of the forests that grow on them, erratics are often hard to spot, except when they are exceptionally large.

A relatively low mountain to the west of the Great Sacandaga Lake has a ridge running from its summit that features dozens of fairly large boulders of gneiss and anorthosite, transported from the High Peaks of the Adirondacks.  Just below the mountain’s summit is a gigantic erratic, split down one side by frost wedging and the action of tree roots.

Far larger than Bubble Rock, it sits on a much gentler slope, and, located as it is in some fairly remote wilderness, it has likely had few visitors.  Doubtless, hundreds more like it are scattered throughout the Adirondack fastness.

But we in the Albany area do not have to look far to find glacial erratics.  Anyone who lives outside of the city of Albany — especially in the Altamont and Voorheesville area on the west side of the Hudson and in the Wynantskill and East Greenbush area on the east side — has found the same problem as the New England farmer in attempting to dig on one’s property:  the enormous quantities of rocks in the soil.

They may have many different points of origin, of course, but one that is very common is a purplish rock often found as a smooth cobble or boulder, deposited directly by the ice or perhaps rounded and polished in a vigorous stream pouring off the melting glacier.  These are samples of what is called the Potsdam sandstone and they originate far to our north near the border with Canada.

The fact that erratics’ points of origin can be determined with precision is useful to glacial geologists, who sometimes refer to deposits of such rocks as boulder trains.  Appearing in more or less straight lines that strike roughly north-to-south, they allow the directional motion of the glacial ice to be determined very accurately.

When I am conducting geologic field trips, I usually toss out this question to participants:  Just how long ago was the Ice Age?

Unless respondents are exceptionally knowledgeable, answers are usually accompanied by a shrug of the shoulders:  “A million years ago?”

That is not a bad answer as a million years ago the ice was, indeed, in control of much of this part of the world.

But people are often unaware that even 10,000 years ago there was glacial ice on some of the highest peaks in the Northeast, and that we are living in what geologists call a glacial interlude.

But aren’t we in a time of global warming?  Yes, there is evidence of that assertion.  But all evidence is that the warmest Earth has been in the last 20,000 years occurred 7,000 years ago in a time geologists call the “hypsithermal,” and the glacial ice is poised for its return in a few thousand years.

In a few weeks, we will be entering the first stages of fall, and the average day-to-day temperatures will begin to drop.  From time to time, we may see exceptionally warm days — we can all remember days in October and even November when the thermometer incongruously hit 80.  But no one is foolish enough on such days to think that summer is coming back.

We are living in a geologic period of continental glaciers and the little purple stones in your backyard not only tell us that the last glacial advance was not so long ago; they may be harbingers of cold, cold days to come!


— Photo by Mike Nardacci

Deer carcasses rot in a sinkhole with waters that have been dye-traced to a spring over a mile away.

To anyone with an interest in the geology of the Helderberg Plateau, one of the pleasures of late March and early April is to take a drive around its back roads to see what the waters of the spring melt-off are doing.

When the snowpack of the plateau is subjected to the first temperatures in the 40s and 50s — especially when combined with a soaking spring rain — the cliffs and valleys gush with waters; their musical sounds signal that, though temperatures may yet perversely drop to unseasonably cold levels, the arrival of spring is irreversible.

And especially in regions with karst topography — where limestone bedrock has dissolved away to produce sinkholes and caves and springs — gullies that are normally dry may be flowing with temporary streams that vanish suddenly into gaping sinkholes, or spring unexpectedly from the ground, producing gurgling freshets that will be dry by early summer.

One chilly day about two weeks back, when the ground still had large patches of crusty snow and temperatures hovered near freezing, I took a drive along a gravel road not far from the hamlet of Knox to a monster sinkhole that lies much less than a stone’s throw from that road.  It is large enough to show on topographic maps, and a geologic map of the rock layers (“stratigraphy”) of the area shows that, in its steep-walled, 50-foot depth, it punches through the surface Becraft limestone bedrock into the underlying New Scotland limestone.

Its picturesque rocky walls often drip with runoff and in warm months are green with mosses and ferns and wildflowers.   At any time of year, it may take a stream and the waters have been dye-traced to a spring well over a mile away, indicating that somewhere beneath its muddy, rubble-strewn bottom there is a cave of considerable size.

Since I was a college student, I have been watching this sink, hoping that some fine day, following the spring floods, enough of the debris will have been washed through to admit explorers to the cave’s uncharted reaches: every cave explorer’s dream!

What I saw through the driver’s window even before I got out of my car unnerved me:  I could see a couple of discarded tires littering one wall of the sink and, when I stepped out and could see the bottom, I spied several more.

But then I saw something far worse.

Directly in front of me, less than 20 feet down into the sink, were a number of rotted deer carcasses, perhaps half a dozen in all.  The lowest ones were nothing but skeletons but those closest to the road still had hide.

Fifty feet or so to the right was another, and there appeared to be two more farther around below the rim of the sink, all of them perched on its steep walls, meaning that, when rain fell, it would pass through the carcasses and sink through the debris at the bottom, eventually finding its way to the cave system’s resurgence point.

I could just imagine what kind of crud and disease the carcasses might carry and all of it would be in the waters flowing from the unsuspecting owner’s spring.

The alluring sinkhole had become a dumping ground.

A week later, I returned with a camera and a friend, long-time caver Thom Engel, a retired Department of Environmental Conservation employee.   This day was substantially warmer than the week before — now temperatures were in the low 60s, meaning that anything that had been frozen on my previous visit was likely to have thawed.

And no sooner had we stepped out of the car when we were hit with a slow breeze that carried the pungent, frightening stink of carrion.  Besides the decayed corpses of the several deer and the rejected tires, there was other less-identifiable trash visible in the bottom of the sinkhole.

I quickly shot a couple of pictures and then we got back into the car and sped away from the vile-smelling vapors carried on the breeze.  So much for the poet’s “gentle springtime zephyrs.”

It has long been illegal to dump waste into surface streams; what landowners today would pour used oil or dump the carcasses of dead domestic animals into a stream passing through their property? And, in any case, their downstream neighbors would be quick to see where their stream is picking up its filth.

Yet generations of people living on karst topography have seen sinkholes as tempting places in which to dispose of waste.  A sinkhole, after all, may be very deep: a fire in the chicken coop kills a hundred hens, the work horse or ox goes to its reward, the much-worked-on pickup truck finally rolls over and dies — and the dead creatures or vehicles are dumped into a handy sinkhole, covered with a couple of tons of “clean fill” — and voila!  The dead stuff is gone forever.


Sinkholes are not the “black holes” of modern astronomy and science-fiction, and a trip into them is not one-way. Soil — especially when it lies thickly over bedrock — can be a natural filter, and small amounts of pollutants can be trapped in subsoil as water infiltrates down to the water table.

But in landscapes with limestone bedrock exposed, surface streams frequently flow into sinkholes and then directly into karst aquifers — or “underground streams” to put it simply — and contaminants can enter the water table in a matter of moments.

There is no filtration of pollutants and extensive cave systems can carry them for miles, even under hills and ridges.  Pity the landowner who discovers that the formerly pristine water source that springs from a mossy fracture in a cliff is suddenly redolent with the odor of anti-freeze or the stink of animal carcasses; and try to understand the bewilderment of a farmer perhaps miles away who cannot understand how the burned-out washing machine and the corpse of the cow that were buried in the convenient sinkhole that lies in a hedge row on his farm is polluting a spring that might be in the next township.  After all — his ancestors have done that for generations, as other trash-laden sinkholes on the property bear witness.

But to understand is not to excuse.

I have deliberately been vague as to the whereabouts of the sinkhole that is the subject of this article and that has become a vile dumping ground.  But what is going on there is illegal, and the New York State Department of Environmental Conservation has been informed of its exact location.

I am hopeful that those responsible for this disgusting flouting of the pollution laws — even if they are not apprehended — will at least read this, know that their crime is now public knowledge — and cease and desist.


Editor’s note: Bob Loden owns the land on Middle Road in the town Wright with this sinkhole and says it has been in the family since 1918. He is 65 now and, for as long as he can remember, people have dumped in the sinkhole.

He is well aware of the cave beneath it — as a young man, he explored Skull Cave, also on Middle Road — and says that, when a dye test was run on the Loden sinkhole, the dyed water flowed out of Bogardus Spring, near Route 433, which is “a couple of miles away as the crow flies.”

Loden went on, “Unfortunately, shall we call them local residents, feel that it’s a place they can throw all sorts of things...We have to get in there and clean all the crap out.” In the past, when the Lodens have found out who threw items in the sinkhole, they have had them clean it up.

“There are some people we feel are repeats and we’d love to catch them,” he said.

Loden said that there are quite a few sinkholes in the area — some larger than the one featured in the column — but its proximity to the road is what draws the waste.

On Wednesday, Loden said, the sinkhole was filled nearly to the brim with water. “A lot of times, things that float wash out,” he said.

— Melissa Hale-Spencer


Well, this winter, a couple of times they got it right.

Although in both of the storms that hit Albany in late January and the first week of February the Weather Channel and other local channels were at first a bit uncertain about the amount of snow Albany was going to get, they all were calling for  “significant” amounts of snow well in advance of the first flakes.

That term is, of course, nicely ambiguous.  If you have to brush off your car, that’s “significant.” It’s also “significant” if you have to shovel a path to get to that car.  And, when schools start closing down and commuters are urged to get an early start and the forecasters start calling for “six to twelve inches or more of snow” — well, that is “significant” in anyone’s estimation.  It’s a term that covers every forecaster’s tail.

And, here in Albany, the fluffy stuff piled up generally in excess of 11 inches in both storms with a good bit more in the higher elevations.  All those kids who gambled on snow days by not doing their homework got extensions and all their teachers got to sleep in.

When I was teaching high school Earth Science, my snow-day mornings consisted of rising late, making French toast, and having that extra cup of coffee while gazing out at the falling snow and thinking of how great the skiing was going to be on the coming weekend and marveling that the forecasters had gotten it right.

But, of course, how many times have we Albanians seen the forecast go awry?  The weather maps show a menacing-looking front advancing from the west or a sinister mass of counter-clockwise swirling clouds lurking in the Gulf of Mexico and poised for a run at the Northeast like a cougar.

The alarms are sounded, people rush to supermarkets to load up on milk, bread, and toilet paper in anticipation of a recurrence of the Great Blizzard of 1888 (and apparently believing that the city snow-removal systems are also rooted firmly in the 19th Century) — and then the storm arrives and delivers a scant inch or two, or a dusting, or nothing at all.

And the folks who do the TV weather come on looking embarrassed and utter some variation on, “Well, folks, this is what we thought would happen but”—pause for a giggle—“darned if that old storm just didn’t deliver.”

Albany area weather

is tough to predict

But, at least in the Albany area, when the forecast for a snowstorm fizzles, we need to cut the meteorologists some slack, for scientists who study the weather will tell you that the Albany area is one of the most difficult places in the contiguous 48 states for which to forecast the weather.

And much of the blame can be laid upon our geography, resulting in a phenomenon known as the “Orographic Effect.”  The term — as with many scientific terms — comes to us from the Greek:  “oros” meaning “mountain,” and “graphein” meaning “to write.”

Without going into the evolution of the term, suffice it to say that it is meant to convey the concept that “mountains write their own weather forecasts.”

Anyone with a high school student’s understanding of science is aware that the temperature of the Earth’s atmosphere decreases with elevation above the surface.

This is why, on a summer day when the temperature at ground level may be in the 90s, the high, wispy cirrus clouds that frequently appear in the sky, heralding a change in the weather are made of ice crystals: They may form at elevations of five or six miles or higher where the temperature hovers at around 85 degrees below zero. This is also why visitors to the big island of Hawaii are astounded to hear of snowboarders racing down the slopes of the great volcano known as Mauna Kea with its summit approaching 14,000 feet above sea level.

Once you get more than a couple of miles up, it’s very, very cold.

This simple fact explains why a mountain may get snow when the surrounding countryside gets rain; it also explains why higher elevations get greater amounts of snow than the lower elevations during a storm: The colder temperatures form lighter, fluffier snow that tends to accumulate to greater depths.  So Albany gets 14 inches of snow and Berne gets 24. Q.E.D.

But, as it happens, the Orographic Effect is far more complicated.

To begin with, it is colder at high elevations than it is at lower ones because the air pressure on a plateau or a mountaintop is lower than it is at sea level, and it drops off dramatically with increasing elevation.  There are simply fewer air molecules to bump together and produce heat by friction.

Anyone who has ever experienced “altitude sickness” driving over the Rockies or skiing on them understands this: It is harder to breathe at that elevation because the lower density means lower amounts of oxygen with each breath, and, for some people, this can cause nausea and headaches.

Of course, for mountain climbers, the region above 24,000 feet on a mountain such as Everest is known as “the death zone” because no one can long survive on the pitiful amounts of oxygen that remain at that altitude.  Our ears pop when we ride an elevator or drive rapidly through changing elevations as the air within our heads adjusts to the change in ambient pressure around us.

Now another concept becomes important in understanding the Orographic Effect, and this is the relationship between what is called the dew point and the temperature of the air mass around it.

The dew point is the temperature at which a given mass of air would become saturated — that is, have a relative humidity of 100 percent — allowing condensation and perhaps precipitation to begin.

It is determined by a number of factors, chief among them the amount of water vapor a mass of air is carrying. The closer the air temperature is to the dew point, the greater the likelihood of condensation followed by precipitation; when they are equal, these results are all but certain.

Now envision a mass of air with a temperature of 28 degrees F and a dew point of 20 degrees F that is moving toward a mountain or mountain range.  The mountain or the range represents an obstacle to that movement: A single mountain will cause a portion of that air to rise and, as it does, both its temperature and dew point will drop with increasing elevation, but the temperature drops faster than the dew point.

The two numbers soon coincide, and voila!  The mountaintop experiences precipitation — which, given these temperatures, will likely be in the form of snow.  At temperatures above 32F, the mountaintop may be capped in fog or experience rainfall.

The accompanying photograph was taken from a high slope of Cadillac Mountain in Acadia National Park in Maine on a humid summer morning.  It shows the islands of Frenchman Bay capped in morning fog while the area around the islands remains clear.

The wind is carrying the moisture-laden air just high enough so that the dew point and air temperature have met and the air has become saturated on both the wind-facing or “windward” slope of the islands and their tops.  Fog forms.

Adiabatic warming

But air that has been forced upward by increasing elevation continues its forward movement and eventually begins to descend.  Now another phenomenon known as “adiabatic heating” comes into play for, as the air moves into elevations of decreasing altitude, both the ambient air pressure and temperature increase, moving the air temperature and the dew point farther apart. The result is a drier, warmer air mass on what is known as the “leeward” slope of a mountain.

Now — take a look at a topographic map of eastern central New York State: the city of  Albany is surrounded by mountains and plateaus.  To the east rise the Berkshires and to the west looms the Appalachian Plateau, locally called “the Helderbergs.”

South of Albany are the heights known as “the Catskills,” which, to just about everyone, sure look like mountains, but are described by geologists as the steep eroded remnants of an ancient plateau.  No matter:  the Catskills are high, exceeding 4,000 feet in a couple of places.  (Of course, north of us are the great Adirondacks, but storms seldom if ever approach the Albany area from due north.)

However — storms at any season commonly approach us from the south, southwest, or east and to reach us they must rise to great heights as they pass over mountain range or plateau — and then dive into the Hudson Valley — a textbook demonstration of the Orographic Effect.

And so, a winter storm approaches from the southwest and Rensselaerville gets 26 inches of snow while Albany gets 10;  a snowstorm moving toward us from the south brings a foot of snow to the ski areas of the Catskills but two inches falls in Albany; a huge “Nor’easter” roars up the coast, dropping a foot and a half of snow on Worcester and Pittsfield, both on the windward side of the Berkshires — and Albany on the leeward side gets two inches of wet snow, or one inch, or rain.

And sometimes the adiabatic warming effect can be sufficient to cause Albany to get nothing at all.

All of this is, of course, a very simplistic explanation of the factors that affect the weather in Albany, and there are many other variables.

But the Orographic Effect neatly explains why the cities of Denver and Colorado Springs have desert climates while a few scant miles to their west the high, thickly forested slopes and valleys of the Rockies may lie under many feet of snow; it accounts for the fact that Seattle is notorious for rain while to its east —  beyond the down-slope of the Cascade Mountains — Spokane’s climate is arid.  And it is why Keene Valley and the western shore of Lake Champlain may have little or no snow when Lake Placid and the High Peaks of the Adirondacks may be buried in the snows of deep winter borne by winds from the west.

And it also may be the reason for the discomfort of your local meteorologist — forehead perspiration easily visible in HD — who opens a weather forecast with a nervous smile and begins, “Well, everybody, here’s what those computer models said was going to happen….”

Standing on the shore halfway down the length of Ballston Lake with a young research assistant named Devin Delevan, I suppose I could be forgiven for mistaking the lake for a river: It is obviously a great deal longer than it is wide, though it shows little of the bending that any proper river should exhibit as it follows the lay of the landscape.

The false impression is quickly dispelled with a glance at a map of the region, for it can easily be seen that the lake lies in a narrow valley, fed mainly by local runoff and some small feeder streams, and empties into the rather unimpressive Ballston Brook as its waters make their way via Round Lake to the Hudson River.

Long, narrow, straight lakes are common in areas that once lay under glaciers. Throughout the Adirondacks, melting glaciers left water in fault valleys called “grabens” that are partially dammed up by the glacial sediment known as moraine.  The Ausable Lakes, the Cascade Lakes, and Lake George are impressive examples.

But Ballston Lake has a different history.  Thousands of years ago, highly energetic waters of the ancient Mohawk River flowed through the valley now occupied by Ballston Lake.  But the river abandoned the valley, leaving the quiet lake as a reminder of how the melting Continental glacier altered the landscape of New York State.

Envisioning the ancient past

In nearly every geology course I have taken, students have been told by the professor that to truly understand historical geology one must have a good imagination: To envision, for example, this part of North America during the Devonian period, 400 million years ago, when it lay under a warm, shallow sea; or during the Mesozoic Era when dinosaurs roamed the lands that would become New York and New England, leaving their bones in sediments-turned-to-rock that have almost entirely been eroded away, except for a few places such as the Connecticut River valley;  or the end of the Great Ice Age, some 15,000 years ago, when the northern parts of New York State still lay deeply buried under the steadily retreating edge of the Continental ice sheet.

But, at that time, the whole upper half of the country was coming out of the last great advance of the ice, leaving much of the Midwest flowing with rivers and streams from the melting glacier, many of them now shrunken or vanished entirely.  A map of the Midwest then would look very different from the way it looks now, for the present Great Lakes had not yet formed.

Instead, the basin in which Lake Ontario sits was occupied by a much larger body of water that geologists call Lake Iroquois, which derived some of its water from proto-Lake Erie and from a huge lake farther west known to geologists as Lake Alqonquin, which would eventually evolve into Lake Huron.

Today, the Great Lakes drain into Lake Ontario via Lake Erie — and Niagara Falls — and thence into the St. Lawrence River en route to the Atlantic Ocean.  But, in those ancient times, what would eventually be known as the St. Lawrence River Valley was under a mile or more of ice, and the massive Continental glacier blocked melt water from flowing directly to the ocean.

Hence, the water found its way through the ancient form of today’s Mohawk River, a river vastly more voluminous and powerful than its relatively placid modern descendant.

Today the Mohawk’s source is considered to be Lewis County, but, around 13,500 years ago, it carried the waters of Lake Iroquois, which seems to have undergone what geologists call “catastrophic” drainage.  This likely was caused by the rupture of an extensive ice dam, and the turbulent flood waters cut a broad valley across the middle of New York State.

The steep cliffs that tower over the Mohawk west of Amsterdam and the wide, deep potholes that are cut into the bedrock of its banks in many places testify to the volume and power of its surging waters.  And the Mohawk today — along with many other streams scattered across the northern part of the continental United States — is classified as an “under-fit” stream, meaning, simply, that it is but a remnant of its former identity as a voluminous, highly erosive river.

Evidence of this fact is easily visible to motorists on the Northway. About a mile south of Exit 12, drivers pass through a broad, deep valley that stretches east toward the Hudson River and west toward Ballston Lake. On its north side are visible once-rugged cliffs that are now softened by years of erosion and tree growth. At the bottom of the valley flows only the gentle Ballston Brook, offering barely a hint of the great and powerful flow that once cut down through the bedrock.

Where did the river go? 

But this scene triggers the question: Where did the river go and why did it go there?

The answer, as with many geologic questions, lies in the distant past.  As the Continental glacier retreated from New York State nearly 15,000 years ago, the Hudson River Valley — which carried an enormous volume of the glacial melt water — became blocked somewhere near Newburgh.

The blockage was presumably made of moraine and it formed a gigantic natural dam.  Its effect was to create to its north an extensive body of water known to geologists as Glacial Lake Albany.  The lake stretched at least as far north as Glens Falls, and probably resembled Lake George and Lake Champlain, both of which were left by the retreating glaciers.

To the north of the natural dam, the east and west sides of the Hudson Valley have fairly steep profiles until the Albany area is reached, which kept the lake relatively confined and narrow.  But, at Albany, the west side becomes a broad, gentle upward slope, and so the lake was at its widest in the Albany-Schenectady-Troy area, stretching east on a line that probably closely followed today’s Route 4 — only a couple of miles from the river — but west as far as Schenectady.

This meant that the Mohawk River — which at that time was carrying massive volumes of water and sediment from western New York State and the proto-Great Lakes — did not become a tributary of the swiftly flowing Hudson as it is today above Cohoes but was a standing body of water.  And, when rivers do this, they slow down and begin to deposit their massive loads of sediment.  The result is the development of a delta.

For examples, think of the Mississippi Delta or the delta of the Nile River.  The Pine Bush of Albany County formed, and numerous sandy pine barrens to the north of Albany along today’s Hudson River show the presence of other, smaller interlocking deltas as well.

Within deltas, rivers break up into what are called “distributaries” — networks of lacy, interwoven smaller streams and perhaps two or more larger ones.  Given the vagaries of seasonal changes in the volume of water and sediment being transported, these distributaries are subject to sudden, rapid changes in their paths.

At some point in the distant past, a distributary of the ancient Mohawk found its way into the valley that today holds Ballston Lake, and the cliffs in the lower part of the valley testify to its erosive power.  But as the Continental ice sheet retreated farther and farther to the north, the St. Lawrence Valley became ice-free and, as the volume of water in the proto-Great Lakes decreased, it was able to find its way to the Atlantic Ocean through that newly exposed, lower-elevation channel.

The distributary of the Mohawk that flowed through the area now occupied by Ballston Lake was deprived of its major source of recharge, and the lake was left behind as a remnant of its once-significant role in the drainage patterns of New York State.

So, the next time you are headed up the Northway — take a moment as you approach Exit 12 and observe the valley over which the road crosses. Let your imagination  carry you back 15,000 years and picture a powerful river sweeping down from the west, carrying with it melt water and sediments from the vast retreating ice sheet, bound for the great body of water called Glacial Lake Albany.

If you can envision them, perhaps a herd of wooly mammoths or a mastodon or two may lumber aside the rushing waters:  This was New York State in the twilight of the Great Ice Age.