Art Is In The Eye Of The Beholder!
Quick Description: In 1977 a commissioned stone sculpture
was installed in a small park in the city of Hartford. The artistic
merits of the sculpture have been debated ever since. The sculpture
consists of 36 large stones placed in rows by the sculptor, Carl
Andre. The first row has a single stone, a brownstone boulder. The
second row has two stones slightly smaller and each succeeding row
has one additional stone so that the eighth row has eight small
stones. No matter what your opinion of this art installation, it
provides us an opportunity to make some geologic observations in
the middle of a city where there are no outcrops.
Location: Hartford, Connecticut N
41o45.875’ W 072o40.503’
Date listed:
Waymark Code:
Listed by: CTGEOSURVEY
Purpose: This EarthCache is created by the Connecticut
Geological and Natural History Survey of the Department of
Environmental Protection. It is one in a series of EarthCache sites
designed to promote an understanding of the geological and
biological wealth of the State of Connecticut.
Supplies:. Bring a copy of this write to answer the four
questions.
Directions: This cache is located on Gold St in downtown
Hartford between Bushnell Park and Main St.
Long Description: The stones are all native to
Connecticut and probably all were found near Hartford. They are
both glacial erratics and large blocks broken from ledge in a
quarry. Perhaps some were derived as free-fallen rocks from the
base of a cliff. The most abundant rock (47%) is traprock, which
underlies all the major ridges and mountains in central
Connecticut. The second most abundant rock is brownstone (25%),
which underlies most of the rest of central Connecticut. Various
igneous and metamorphic rocks make up the remaining rocks. Note:
“Traprock” is a generic layman’s-term designating an igneous rock
(rock that forms from the cooling and solidification of once molten
rock) of basaltic composition with a fine grain-size. In
Connecticut traprock consists mostly of extrusive igneous rocks,
congealed lava flows that resulted from volcanic eruptions about
201 million years ago. Included also are the intrusive diabase
dikes and other bodies that formed in the fissures through which
magma that fed the lava flows, rose to the earth surface 201
million years ago. “Brownstone” is likewise a generic layman’s-term
used to designate the reddish-brown
sedimentary rocks of central Connecticut. More specifically, it
is a quarryman’s term to designate pinkish-gray to reddish brown
sandstone that is cut and used in building. Some of the brownstone
boulders used by the sculptor are indeed sandstone, but some are
siltstone.
The waymark above is at a plaque that we will use to reference
the beginning of our geologic tour. The first row of the sculpture
is just east of the plaque. The stone that makes up the plaque may
not be from Connecticut.
Question #1: What is the name of the
sculpture?
Because traprock is the most abundant rock in this sculpture, we
will look first at some of the interesting features in those rocks.
Many of the traprock boulders of the
sculpture contain small and large
holes that were formed by bubbles of gas that could not escape
before the molten rock around them congealed. Gas bubbles
frozen in the lava are called vesicles unless minerals have
filled inside them, in which case they are called amygdales.
Magma (molten rock; lava is the term for molten rock when it
erupts at the ground surface) is forced out of the earth, in
part, by expanding bubbles of gas. Most of the gas escapes as
soon as the magma reaches the surface.
The gas that forms vesicles has two origins. 1). It is dissolved
in the magma/lava and comes out of solution (much the same way that
carbon-dioxide bubbles come out of solution when you pour soda, or
any carbonated beverage, into a glass). Coincidentally, carbon
dioxide is one of the most common gasses to bubble out
of basaltic lava in many modern volcanoes. Water vapor and sulfur
gasses are also common. The gas bubbles naturally float upward
through the basalt lava and although most escape to the atmosphere,
a few get caught when the lava cools sufficiently to harden.
2. Gas also may be introduced into lava when a flow comes out
over wet ground or into a shallow body of water. The water turns
into steam that then bubbles upward through the lava. This process
may form large vesicles. Vesicles found at the base of a lava flow
likely originated by this process. Air, in unusual circumstances,
may be introduced into the base of a rapidly advancing flow. Large
vesicles could form in this manner.
At least three kinds of vesicles can be found in various stones:
i. small spherical holes about half centimeter or less in
diameter that formed near the top of a lava flow; ii. long
vesicle cylinders about a half centimeter in diameter and several
centimeters long that formed as steam more or less continuously
bubbled up from the substrate; and iii. “half-moon” vesicles
convex-upwardly curved vesicles 5-20 in diameter with flat bottoms
or upwardly curved bottoms that formed when large volumes of gas,
either steam or trapped air, rose upward through the lava. When the
basalt boulders containing the half moon vesicles were placed in
the sculpture, the artist paid no attention to the orientation of
the stone relative to the orientation it had when the vesicles were
rising through the molten lava. Careful observation by you of the
rock closest to the road in the 5th road will allow you
to tell that the half-moon vesicles, which at their formation were
rising upwards, are now oriented sideways.
Question 2. If you drew (but please do
not) an arrow on the rock nearest the road in the
5th row that pointed in the direction that the half-moon
vesicles were rising when they formed (that would be the
“up-direction” of the rock at the time of its formation), in which
direction, toward the road or toward the cemetery, would it point
as the rock is oriented now?
If you look carefully at the rock closest to the road in the
4th row, it looks like it is made up of long,
blocky-fragments of vesicular basalt. It is a rather lumpy looking
rock. Some of the fragments and some of the vesicles contain
deposits of a white mineral. This rock formed at the top of a flow
when
the turbulence of the advancing flow broke up a thin
skin of congealed lava. Many of the broken fragments formed a
rubble accumulation at the top of the flow. Some may have sank back
into the flow and remelted. We call this a flow-top breccia.
Another interesting observation can be made by looking under the
stones of the sculpture. Many seem to be perched on a short
pedestal of soil that may be several centimeters high. This
observation can be attributed to soil erosion that has occurred
since the installation of the sculpture. In addition many roots of
the trees are exposed also caused by soil erosion. The pedestals,
which are 2-5 centimeters (1-2”) in height, are preserved remnants
of the original soil layer upon which the stones were placed. If
you think back, you probably can remember seeing similar situations
before, perhaps around your home, school, place of work, or in a
park. Soil erosion occurs at significant rates, even greater than
here, in many places. You might say, “That is only a few
millimeters/year….nothing to be alarmed about.” But project that
rate for only a hundred years and consider the volume of soil that
is removed. It all goes somewhere and where ever it ends up will
have its environment degraded by siltation. Siltation is hazardous
for many organisms.
Question 3. Calculate (OH NO! Not math…you know
I hate math. Ugh!!!) the thickness of soil that could be eroded in
100 years if the current rate of soil erosion is not
checked.
There are many interesting rocks in this sculpture. The last we
will mention is the third rock from the north in the eighth row.
This rock is covered by golden feathery -like crystals of a mineral
called tremolite. This is an uncommon rock in Connecticut. It is an
ultramafic rock, rich in iron and magnesium.
Question 4. What is the waymark of this
rock?
How do people respond to this EarthCache? Answer the four
questions.
Difficulty: 1.5
Terrain: 1
Type of land:
EarthCache category: Geologic art