Picture of the Week - Stark's Knob

The picture below is of Stark's Knob - a rocky hill just north of Schuylerville, NY.  It's near the banks of the Hudson River and about 10 miles east of Saratoga Springs.  This hill tells two stories which are separated by around 450 million years of time.

Let's start with the more recent story first.  It happened only 233 years ago...

As summer moved into fall in 1777, the Revolutionary War wasn't going well for the colonists.  The British General John Burgoyne from Quebec was planning to move down through Lake Champlain and then into the Hudson Valley.  British troops were also supposed to be led from the Great Lakes down the Mohawk Valley toward Albany.  Finally, General Howe was to have come up the Hudson Valley from New York City.  These three advancing columns were to meet up and effectively divide the colonies in two - the war would soon be over and the British victorious.

It didn't work out as planned.  The column from the west got held up at Fort Stanwyx near the present-day city of Rome, NY, where they met fierce resistance.  Through an apparent miscommunication, General Howe sent his army to Philidelphia that fall, rather than up the Hudson.  It was left to General Burgoyne.

It all culminated at the Battle of Saratoga - really a series of skirmishes in September and October.  General Horatio Gates and Major General Benedict Arnold commanded the American forces.  If Arnold had died at Saratoga, he would be remembered today as a great American hero for his actions there.

The Battles of Saratoga did not go well for the British and by October 10 they were under seige by the Americans.  As Burgoyne attempted to retreat to the north, General John Stark "corked the bottle" by positioning his troops between the Hudson River and the hill now known as Stark's Knob on the 12th trapping the British and leading to their surrender a few days later.  This major defeat of the British is seen by many as the turning point of the war.

 The Surrender of General Burgoyne by John Trumbull (1822)

It's a great story and when standing on top of Stark's Knob, one can visualize in your mind's eye those long-ago movements of troops across the landscape.  To a geologist, however, Stark's Knob has another history, this one stretching back some 450 million years into the past.  Below is a close-up of the rocks forming the knob.

What is this?  Turns out it's basalt - hardned lava.  Not just any basalt, either.  It's pillow basalt (note the rounded shape).  Pillow basalts form when lava is erupted under the oceans - the cold water instantly cools a rind around the erupting lava and it oozes out like toothpaste being squeezed out of a tube forming rounded masses on the seafloor.

Why was this seafloor and why was lava erupting here?  Turns out that 450 million years ago, this part of proto-North America was south of the equator and under water.  It started out as a shallow continental shelf but became downwarped into a deeper basin as the seafloor was subducted down an approaching trench.  The trench was the plate boundary between us and a chain of volcanic islands relentlessly approaching closer each year.

Image from the United States Geological Survey (USGS)

As the island arc approached, the seafloor flexed downward, fractured, and erupted lavas.  Eventually the volcanic arc collided resulting in a mountain building event called the Taconic Orogeny - Rocky Mountain sized peaks right here in eastern New York State!  That collision thrust up a slice of the ancient seafloor and emplaced it here near the banks of the present-day Hudson.

Both stories are interesting and I share both when periodically bringing students to this neat site.  It's great to get students to think about connections between various disciplines like history and geology (which is really just history extended far, far back beyond humans).