Tuesday, May 26, 2015

Niagara Falls Erosion - Part I

In my last post, I mentioned that the Army Corp of Engineers "turned off" the American side of Niagara Falls back in 1969 to deal with erosion issues.  So how fast do the falls erode?

Here's a cross-section of the geology at the falls.  There is one important (for our purposes) rock formation here - the Lockport Dolostone (also called Dolomite but I prefer Dolostone) which is underlain by a few different sandstone and shale units.

Dolostone is similar to limestone.  Limestone, a very common sedimentary rock, is made of the mineral calcite - CaCO3 (calcium carbonate).  Dolostone, on the other hand, is basically limestone with some magnesium substituting for the calcium in the formula (which creates the mineral dolomite) - CaMg(CO3)2.  This generally makes it a harder, more resistant rock than limestone.

Outcrop of Lockport Dolostone commonly seen in the area

The shales underneath are much softer and more easily eroded.  Here's a local example of similar differential erosion near Lockport, NY (Whirlpool Sandstone and Queenston Shale - see cross-section above).

Since the Lockport Dolostone is so hard and resistant, and is slightly tilted (dipping to the south), it doesn't weather as much as the surrounding shales and erodes to form a prominent cliff called the Niagara Escarpment.

The Niagara Escarpment runs over a large area from western New York, through Ontario, along the Upper Peninsula of Michigan, and then into Wisconsin (red line in map below).

We're only concerned with the escarpment where it crosses the Niagara River between Ontario, Canada and New York State (note the dipping Lockport layer).

The Great Lakes and Niagara River formed after the most recent Ice Age (the sequence of their formation is a bit complicated so I'll avoid that here).  Basically, Niagara Falls formed at the Niagara Escarpment around 12,300 years ago and has been eroding upstream since then carving the Niagara Gorge through the Lockport Dolostone.  The Dolostone ledge forms the resistant caprock to the falls (without this resistant rock unit, the Niagara River would descend from Lake Erie to Lake Ontario in a more gentle slope with no major waterfalls).

The American Falls pouring over the Niagara Escarpment

Since Niagara Falls is currently around 11.4 km (7.1 miles for those of us in the U.S.) from the Niagara Escarpment, and took 12,300 years to erode that far, how fast is the average rate of erosion here?

(7.1 mi / 12,300 yr) = 5.8 x 10-4 mi/yr x (5,280 ft / 1 mi) = 3 ft/yr

Three feet every year - that's pretty fast!  The problem, of course, is that this is an average rate of erosion over 12,300 years.  Why might this be a problem?  How about an analogy...

If I got into my car and drove to Niagara Falls right now (350 mi), it might take me 6 hours.  A reasonable assumption is that I took the New York State Thruway and traveled at 58 mph (350 mi / 6 hr).  But maybe instead I drove at 70 mph for 5 hours and spent an hour leisurely eating dinner at a rest area.  Or maybe I drove at 90 mph for 1 hour, got pulled over for a ticket for a half hour, and then drove 58 mph the rest of the way paranoid about getting another ticket.  Average rates don't always tell us specifically what was going on during each moment of time.

So, what was going on during the past 12,300 years?  Was Niagara Falls eroding at a constant rate the whole time or has the rate varied?  We'll examine that in my next post.

Monday, May 25, 2015

Turning off Niagara

Back after a bit of a hiatus now that the spring semester has ended.

A few days ago, my family stopped at Niagara Falls after returning from a geology conference in Madison, Wisconsin (we passed through Canada coming back).

They are impressive falls (two really - the American falls in the foreground and the horseshoe-shaped Canadian falls in the background - separated by Goat Island).

There's a lot of neat stuff I could write about concerning the geology of Niagara Falls but I'll just concentrate on one for today - the time they turned off the American Falls.

They actually slow down the falls each night.  Ontario Hydro and the New York Power Authority pump tremendous amounts of water each night from the Niagara River upstream from the falls to top off their reservoirs.  They do this at night because this action reduces the flow over the falls from 100,000 cubic feet per second (CFS) to 50,000 CFS (half).  During the day, the flow is sort of left alone so the millions of tourists have impressive waterfalls to admire.  By "sort of", I mean that water is still normally diverted for hydroelectric generation 24/7.  Without this diversion, the flow over the falls would be a more awe-inspiring 200,000+ CFS!

Flow over Niagara Falls has actually been stopped (at least partially) three times in recorded history.

The first event was March 29-31, 1848.  People living near the falls noticed an eerie quiet on the morning of the 30th.  When they went to look, they saw a dry riverbed with fish and turtles flopping around.  The falls had maybe 30-40 CFS - a mere trickle.  People were able to walk on the riverbed and collected artifacts from the War of 1812 (muskets, bayonets, tomahawks, and the like).  Special church services were held on both sides of the border for anxious people who didn't understand why the river suddenly vanished.

The cause of this?  Strong winds formed a massive ice jam at the mouth of the Niagara River at Lake Erie.  On the evening of the 31st, however, the jam broke, people heard a low rumble, and a wall of water swept down the dry stream bed refilling the river and restarting the falls.

The next event was man-made.  In 1953, some coffer dams were built exposing only a section of the Horseshoe Falls nearest the Canadian side (where the big tourist center is today). This allowed engineers to stabilize this section of the edge of the falls which were, of course, eroding as falls are wont to do.

The last time the falls were turned off was also a man-made event.  The Army Corp of Engineers built a 600 foot coffer dams to Goat Island which turned off the American Falls (the water was diverted over the Canadian falls) starting on June 12, 1969.  All part of the Corp of Engineers never-ending struggle to control nature and stop erosion (an ultimately impossible task - see John McPhee's The Control of Nature).

Tourist attendance at the falls topped all-time records to see this - they even allowed people to walk out onto the dry river bed.  The Corp of Engineers injected concrete into the bedrock fractures and inserted a bunch of rock bolts over a period of about 5 months.  Once "repaired", the falls were restarted on November 27.

In my next post, I'll talk a bit about erosion at Niagara Falls.

Thursday, December 18, 2014

Nuclear Lake

Believe it or not, there's a lake off Route 55 near Pawling in eastern Dutchess County with the rather unusual name of Nuclear Lake.

How on earth did it get that name?  It's certainly not something the local Chamber of Commerce would choose.  Well, it apparently was named when a former hunting preserve around the lake was purchased in 1955 by an outfit called Nuclear Development Associates.

New York Times - February 18, 1955

The federal Atomic Energy Commission sponsored work there from 1958 through 1972 by a research facility owned by the United Nuclear Corporation.  They were working on the development of plutonium fuel for breeder reactors.

Why did they stop in 1972?  Turns out there there was a little accident.  A chemical explosion in the laboratory blew out two windows on the north side of the building spraying out an unknown amount of plutonium.  After a two-year, three million dollar cleanup, the federal government bought the property for $900,000 in 1979 and declared it fit for unrestricted use.

Today, the Appalachian Trail runs right next to the lake.

The following, from Hike the Hudson Valley, has an amusing take on it all...

I know what you’re thinking.  Why would I ever want to visit a place called Nuclear Lake?  Well, let me set your mind at ease.  The only reason it’s even called Nuclear Lake (you’re going to think this is so funny when you hear it), is that in 1972, a chemical explosion blew out two windows in the experimental nuclear research lab that used to sit on the shore of the lake, blasting an unspecified amount of bomb-grade plutonium across the lake and surrounding woods.

See?  I bet you thought it was something bad.

Okay, so maybe it doesn't sound that fantastic.  But the trails around the lake were extensively tested, cleaned and declared safe many years ago, and who am I to argue with all those Geiger counters?  I’m sure they dumped plenty of kitty litter and sawdust on top of that plutonium.  To visit the place, you’d never know anything untoward had happened at all.
To make it even more irresistible, the website also states that Nuclear Lake is the most beautiful lake on the entire 2,200 miles Appalachian Trail - high praise indeed.

How can you resist that? So today I went for a hike there.  From Route 55, it's a relatively easy walk of a little over 4 miles round trip with a little up and down but, no real challenges.  The Hike the Hudson Valley web site has a great (and accurate) trail description for the loop around the lake.

The walk in was nice, typical terrain for the Hudson Highlands with outcrops of gneiss rock (get the geology pun?) and not much in the way of interesting plant or animal life this time of year (mid-December) other than a few ducks on the lake and squirrels in the woods.

Banded gneiss

Not so green wintergreen underfoot

Arriving at the lake, one sees a fence guarding a berm on the south end (look at the Google map image above and you can see the straight line).  The fence is just to keep vehicles off the berm, it's easy to walk around it.

There's also a cleared area next to the lake which looks to be the site of the old research facility.  Nothing there anymore.

At the east end of the berm is a small stream draining the lake.  But across the lake's outlet is a boom.

So here's my question... If the site was cleaned up 40 years ago, and declared OK for unrestricted use, and nothing exists around the lake anymore, why the hell is there a boom here?  What is it supposed to be catching off this "pristine" lake in the woods?  Strange.

It gets even stranger here.  No, not this growing tree, although it was odd too.  Just wait.

The lake, as advertised, is quite beautiful with a very nice trail looping around it.  I definitely want to return in summer when everything is green (although not sure if I'd swim in this lake).

 View from the south end of the lake

View from the north end of the lake

The best thing about the lake is that it's a mile walk in from the road so that keeps out much of the riff raff.  I had the entire place to myself - not a soul in sight.  I'm sure summer would be a different story, however.

Now for some more strangeness.  At the north end of the lake, there are a bunch of stone walls in the woods.  Not normal stone walls like I'm familiar with - the straight walls that once lined farmer's fields but now lie in the woods as some hardscrabble farms were abandoned a century ago.  No, these stone walls ran up and down hills in curved paths.  Not marking farmer's fields either since no one could farm anything on the steep, stony hillsides around this part of the lake.

A curvy stone wall running to the lakeshore

Another zig-zagging wall

Who the hell builds a rock wall that zig-zags up the hill?  It's certainly not marking anyone's property line.  Another ran parallel the shoreline.  Why do that?

Is there a point to this?

One area had a wall encircling an artificial hill of stone.  It looked like a ritual space to me.

Wall went around this mound

Another wall enclosed a rectangular area but was too sloppy to be a building foundation.

Not a foundation - Again, what's the point?

Very strange.  Who built all of these stone walls (there were a lot of them!) that are running willy-nilly all over the place and why?

Here's another strange thing I've never seen before.  On the trail by the stone walls was an eviscerated bird - headless and gutless (not sure what the bird was, but I assume killed by a raptor).

But wait, if you like strange, it gets even better.  Nuclear Lake also happens to be the site of several Bigfoot/Sasquatch sightings over the years!  Some have claimed that if you take a stick and bang on a tree, you can call a squatch (those in the know call them "squatches").

So, of course, being the type of person I am, at the furthest end of the lake, the place with the odd stone walls and eviscerated bird, I picked up a dead stick and struck a fallen log three times - thump, thump, thump.  Nothing.  No squatches in the area, or so I think.  But 10 minutes later, when I was sitting down on a flat rock on the shore of the lake (hand over my heart and swear to god), I distinctly heard two thumps.  Then two thumps again.  Then, a few minutes later, a weird yowling scream (it kind of sounded like a domestic tom cat but there are no houses within a few miles of this lake).  The ducks in the lake didn't like it either since they started up a loud quacking in response.  Here I am sitting all alone in the woods, not quite helpless but feeling pretty exposed, two miles from the road, feeling chills up my spine.  Cue spooky music.

No, I don't believe in sasquatch, but I have no idea where the thumps came from (sounded like something banging a log just as I did - another squatch caller?).  The yowl may have been a coyote or maybe a bobcat, I have no idea but it was real and spooky.

All in all, an excellent hike (but bring a hiking buddy if you're easily spooked!).

Thursday, December 4, 2014

How much does a millstone weigh?

Not far from the college where I teach is an old millstone laying decoratively on the ground.

I've been doing some research on millstones lately so I was wondering how much a typical millstone like this would weigh.  Measuring it gives the following dimensions:

   Diameter = 53 in
   Thickness = 8 in
   Hole = 13 in square

This millstone happens to be made of Shawangunk conglomerate which is composed almost entirely of quartz.  All geologists know the density of quartz which is 2.7 g/cm3.  I want to keep everything in more familiar units so that corresponds to about 0.1 lb/in3.

The volume (V) of the millstone would be:

   V = π (d/2)2 t

where d is the diameter of the millstone and t is the thickness.

   V = 3.14 (53 in / 2)2 (8 in)
   V =  17,641 in3

We have to subtract out the volume of the square hole in the middle (13 in * 13 in * 8 in = 1,352 in3)

   V = 17,641 in3 - 1,352 in3
   V = 16,289 in3

Now we can multiply this by the density of quartz to get the weight of the millstone.

   Weight = 16,289 in3 * 0.1 lb/in3 = 1,629 lb

Over 3/4 ton!  Imagine moving this many miles, over rough terrain, with man power, a wagon, and maybe a mule or two.