New Hampshire is fortunate to have
such a wide diversity of geologically unique locations, which
allows many opportunities for earth science education.
Pawtuckaway State Park hosts one of the most impressive collection
of large glacial erratics in the world (all these shots were taken
in Pawtuckaway). There are several clusters of these boulders
located in the park, following something of a boulder train and
running for some 2-3 miles in a southeasterly direction. One of the
more popular of these fields is known as "Boulder Natural", which
is the only area you need to physically visit. The whole of this
location measures about 250 ft. by 600 ft. and has little climbing
involved, except over tree limbs and smaller boulders which are
everywhere. Parking is available .15 miles away off of an
unmaintained road. There are two gates off of Reservation
Road that allow access to this road. Note that as of 1/5/2011, Gate
5 is closed but Gate 4 is open and the road is passable in
something of an offroad vehicle. I made it down in 2WD in my
Tundra. There is one questionable spot at N43° 06.193 W071° 11.198.
Make it past that and everything else is easier. If you park at
Gate 5 and hike in, it's about 1.5 miles to the boulder field along
an easily walked road. If Gate 4 is open or if you choose to hike,
it's about 2 1/4 miles each way.
Glacial erratics
are stones or boulders that differ in size or type of rock as
compared to the area in which they rest and have usually been
transported from a different location through the force of ice or
water. The name "erratic" is based on the errant location of these
stones. Although technically they can be as small as pebbles,
generally speaking we're talking about larger boulders (when they
are enormous, some people call them "massives" - Pawtuckaway has
several massives). In researching some background, I came across an
entry in an 1878 geological survey that referred to a particular
"erratic", named "Churchill Rock"; which was purported to be
located in this complex (said to be the largest boulder in
Pawtuckaway and one the the largest in the state). I found it too
ironic not to include with this earth cache the story that the
stone was named after a "lunatic who got loose from his handlers",
and was later recovered after being found to have climbed atop of
said rock - thus one erratic sat upon another. I was
unable to find any further reference online to its exact
whereabouts though there was an obscure reference to its location
in the 1878 report (nothing like a hard set of GPS coordinates to
tell me exactly where to look). In reaching out to the local
bouldering
community, I was able to re-discover this missing
erratic/boulder (still unable to find the erratic named Churchill
though). Your job while learning about glacial erratics is to find
Churchill Rock.
Click here to print out a copy of this image
To get credit for this cache, you will have to
email me with the answers to the following Five questions. I will provide
you with much of the needed information below:
1) Define in your own words the concept
of
glacial plucking (watch
video). The boulders you
will find in the "Boulder Natural" location came from the area near
Devil's Den (GCGEVZ) and were transported to the site by
glacial activity.
2) At ground zero there is a rock
called "Yosemite Boulder" (see pic below). It was transported by
glacial action to its present position and then stood up like a
giant horn (you'll find where a small stream disappears under the
rock and reappears on the downhill side). Such a process puts
substantial stress on stony travelers such as this and as is often
the case when such force is being exerted, this one sustained
several large cracks in it. Stand on the uphill side of the boulder
and find the crack I have partially outlined in purple. The two
halves of the boulder have shifted. Tell me how much the boulders
are offset from one another (note that I have airbrushed out any
tell tale signs in this pic, but you should be able to find those
parts that once matched).
3) Tell me how high the top of
this boulder is.
Print out a copy of this map here
4) Forward me coordinates (photos are NOT
required) of places you found in the Boulder Natural area showing
evidence of glacial striations. I provide a couple of sets of
coordinates to examples in
this short video but if you can find better quality examples in
some of the erratics (that would be considered winter friendly) and
don't mind sharing, feel free to upload good quality photos but
forward me the coordinates where they were located.
5) Find Churchill Rock. It's known
by a different name today and very obscure to find online. You'll
have to explore the area of Boulder Natural to find it (which
you'll be doing anyway to seek out glacial striations). Remember
that it is estimated to measure 62 feet long by 40 wide, and 40
feet high. We're not talking nano here, but you need to see it from
the correct side to confirm your find. This valley of
massives only measures about 600 ft. long by 250 feet wide. If
you're really slick, you can cheat and do some simple geo-math
using the coords from the Boulder Natural map above and narrow down
your search to four possibilities. Tell me the modern name of the
boulder or the number shown in red next to it that you would have
been standing at to view it properly - extra credit if you
climb it and bark at the moon : )
(note that the word "lunatic"
comes from the latin term used to describe one who barks at the
moon)
Some basic background:
Glaciers retreated from
this area between 10,000 and 10,800 years ago, leaving many
erratics in their wake. These boulders have been extracted from the
bedrock through several mechanisms including erosion of adjacent
rock,
fractures due to geologic faults, and by "plucking". The latter
process being the most prevalent in this case. As glaciers encroach
into new areas, they dragged along large deposits of boulders and
gravel, grinding this slurry as they advance. Often times, a
snaking bank of gravel and sediment was left behind, showing the
path the glacier(s) took. These banks are known as moraines and eskers. Sometimes the
boulders themselves are lined up along the path of the flow in
similar fashion (as is the case starting near
Devil's Den (GCGEVZ) cache, continuing through "Boulder
Natural" and continuing as it passes an area known as "Trailside
Boulders", then past the Round Pond Boulder field where
Round Pond Balancing Boulder (GCGCOM) is located, and finally
beyond that to the Blair Woods Boulder Field. It's also interesting
to note that this boulder train of clusters also follows one of the
area's natural fault lines. Erratics usually show scarring from
their journey as deep-cut striations, as
rounding, pitting, polishing or as fractures. Be aware that some
water staining and erosion might appear to be glacial scarring, but
tends to show as vertical grooves because of gravity. It's easiest
to find this evidence on the local bedrock during snow-free
weather. Some rocks have undergone significant tumbling and may not
show any evidence of striations such as in the case of
"Balancing Rock" boulder.
THE STORY OF CHURCHILL ROCK: The
Geology of New Hampshire. Hitchcock, C.H., 1874-1878) tells us
of the following story in this heavily paraphrases rendition (book
starts at N303):
"Although our state is
noted for the great abundance of boulders strewn over its surface,
it is only quite recently that I have seen boulders in our limits
larger than any of which mention has been made in the writings of
American geologists. They were brought to our notice by His
Excellency Governor Prescott. Regret had been expressed to him that
no boulder had been found in the state equal in size to those known
to exist in the neighboring states. As if he felt the credit of the
state impaired by the imputation, he immediately searched the
neighborhood of Pawtuckaway Mountain, and found a very formidable
array of giant fragments superior to anything else described
elsewhere. By example, Churchill Rock of Nottingham was found to
measures 62 feet long by 40 wide, and is estimated at 40 feet high.
Making liberal allowances for irregularities in its dimensions, it
contains over 75,000 cubic feet, weighs 6,000 tons, and is
therefore nearly double the size of the neighboring state’s
examples. Bingham's Rock at Smuggler's Notch in Vermont is larger,
but is so connected with a ledge as not to be properly esteemed an
erratic.
Churchill rock is on the
south side of North Pawtuckaway (North Mountain). It lies in a
valley not shown on our map by contours, starting at the middle of
the Deerfield and Nottingham line where it passes over this peak,
and pointing east to Round pond. This valley is half a mile long,
and displays a very remarkable lot of large boulders and moraines.
The commencement of the valley is a narrow notch in the Sienite of
the mountain, full 200 feet deep and narrow. The boulders seem to
have been detached from the cliffs on either side of the notch, and
then transported by the ice perhaps, or local glacier, eastwardly.
Within a few rods of the starting-point are several large blocks,
worthy of special measurement anywhere except in their company.
About an eighth of a mile down, too far to allow of their
accumulation by gravity, are six large boulders close together,
each one averaging 30,000-35,000 cubic feet. A little beyond them
is Chase rock, 40 feet long, 40 feet high, and 30 feet wide. About
a quarter of a mile or a little less from the starting-point is
Churchill rock, and close by it two others, one estimated as equal
to 30 feet in each direction,— 27,000 cubic feet, and the
other ten feet longer, with the same breadth and height, or 36,000
cubit feet.
Churchill rock received
its name sixty years since, from the circumstance that a lunatic of
that name escaped from his keepers, and was discovered on top of
this boulder. It will be seen that the rock is divided by a
crevice, originally a joint, providing a space usually a few inches
in width. Mr. Churchill must have crawled up through this narrow
opening, doing, like other persons in his condition, what seems
almost impossible. It was found necessary to fell a tree upon the
rock to insure for the man a safe descent. The base of the stone is
below the feet of Gov. Prescott, as represented in the heliotype,
who stands the lowest down of the four persons seen in front. The
top is midway of a pine tree with a trunk nearly two feet in
diameter, and was thought, by some on the ground, to be 80 feet
high."
Still not satisfied? There is a wealth
of information available if you're interested in exploring
additional pockets of Pawtuckaway's Boulders at
Mountain
Project.com
Here is a collection of photos I've
assembled from that site:
Click here for a slideshow of
Pawtuckaway Erratic examples and the erratics who climb
them.
And here are some Youtube.com videos
of people "bouldering" at Pawtuckaway: Pawtuckaway Bouldering Session - by
XXLeeWeeXX, Bouldering at
Pawtuckaway - by MichaeljWyatt, and Overlooked V4 -
by Fafoin25,