Sleeping Giant State Park
Today
you will become familiar with the geology of Sleeping Giant State Park, one of
the favorite hiking sites of many Connecticut residents. Sleeping Giant State
Park is in the central part of Connecticut, in the northern part of the town of
Hamden, which is sometimes referred to as Mount
Carmel. Several maps of this area that you will use contain different kinds
of information about the Giant:
1.
Trails
on the Sleeping Giant:
This simple flier made available by the Sleeping Giant Park Association at the
park entrance shows all of the established trails in the park. Each trail is
coded by color or by the shape of its blaze. A blaze
is a symbol (often a rectangle) painted on trees at eyes’ height along a
trail.
2.
Mount
Carmel Quadrangle Map: This
map is a United States Geological Survey topographic map. This topographic map
shows contour lines at intervals of ten feet that can be used to visualize the relief
or shape of the surface of the land. Topographic maps are highly detailed and
show not only roads and streams but even the locations of individual buildings
that were present at the time the map was made.
3.
Bedrock
Geology of the Mount Carmel Quadrangle, Connecticut: This quadrangle map, published by the United States
Geological Survey, has three parts:
a.
The map itself, which is color-coded according to rock type.
b. An
extensive explanation of the
characteristics of each of the rock types shown
on the map.
c.
Several cross-sections diagrammed in
color to show the kind of rock and the
structure or shape of the rock layers below the
surface. The kind of rock present and
its structure together help geologist’s interpret the geologichistory
of the Sleeping Giant and its surroundings.
The
Mount Carmel Quadrangle map includes a description of the rock types on the map
sheet.
4.
Depth
to Bedrock, Mount Carmel Quadrangle Map: This black-and-
white map uses various kinds of shading to symbolize the depth to
bedrock. Depth to bedrock is really
another way of saying the thickness of the
loose deposits, like sand and gravel, over the bedrock.
5.
Surficial
Geologic Map of the Mount Carmel Quadrangle, Connecticut: This color-coded map indicates the different
kinds of deposits lying over the bedrock. The type of deposit indicates whether
the deposit was made by a river (alluvium), melted water within or beyond a
glacier (stratified drift) or simply dumped in place by glacial ice (till).
Since water sorts sediments by size, alluvium and stratified drift are sorted,
but till is a mixture of many sizes of materials. The map is accompanied by a
booklet explaining the glacial geology in detail.
(Each
group should select a set of maps to work with before beginning the hike.)
1. Find the Gorge Cascade on the Sleeping Giant trail map. The hike will be along this stream. Note where the stream is relative to nearby landmarks such as roads or other obvious features:
2. Use the above features to find the Gorge Cascade on the Mount Carmel topographic map.
3. Locate the
Sleeping Giant on the geologic bedrock map.
4.
Locate the Sleeping Giant on the surficial geologic map. Do the following on the
outline map of the Sleeping Giant below:
Background
Information to Study the Rocks of Sleeping Giant
Rock Composition:
You
already know from the map study you did prior to this hike that a variety of
materials is found on the Sleeping Giant:
1.
Arkose:
Arkose is a
poorly sorted sandstone containing feldspar
that formed from sediments that were once part of the ancient mountains
of Connecticut. When the central part of Connecticut sank as Connecticut was
stretched 200 million years ago, mountain streams brought these sediments into
the young Central Valley. Only the eroded cores of these mountains still remain.
Arkose has a reddish color because of the iron oxide cement that holds its
grains together. (Generations ago arkose was a popular building stone which was
commercially known as brownstone. Some
buildings today are still referred to as brownstone houses, brownstone churches,
etc.)
2.
Conglomerate:
Conglomerate is similar in origin and composition to arkose, but it contains
pebbles as well as sands and clays.
3.
Diabase: This is
igneous rock that is commercially known as traprock
and which formed from magma. The magma squeezed into cracks that opened up in
rock as Connecticut was stretched. This occurred when Pangaea separated into
today’s continents 200 million years ago. Some
cracks reached the surface, causing fissure eruptions of lava that flowed over
Connecticut's landscape, forming basalt.
Diabase has the same composition as
basalt, but its crystals are larger and more noticeable. The magma that produced
diabase was farther from Earth’s surface, so it cooled more slowly giving the
crystals time to grow. The crystals in basalt formed near the surface where they
quickly cooled to microscopic size. (Another rock found in Connecticut with the
same composition as basalt and diabase is gabbro.
Gabbro formed from a magma that cooled very slowly far below the surface; like
granites, gabbro has crystals that are large enough to identify easily and are
called coarse-grained. The crystals in
diabase, which are fine-grained, are
not easy to identify.)
Characteristics
of Deposits Found at Sleeping Giant State Park
1.
Alluvium:
Alluvium
refers to deposits that streams have carried and sorted by size. The size of the
particles that were moved and deposited by a stream is related to how fast the
stream traveled. Steeper streams
travel faster. Likewise, the more water there is in a particular stream, the
faster the stream travels. This is one of the reasons that streams can move
larger objects during floods.
2.
Till:
Till is
unsorted material that was embedded in a glacier or that the glacier bulldozed
at its front. The materials remained in place, unsorted when the glacier
retreated, and are of many sizes.
Figure
1. Alluvium
deposits beside the Mill River in Sleeping Giant State Park.
3. Stratified Drift:
During warm periods of a glacial episode much melting occurs causing
streams to form in cracks inside the glacier as well as beyond it. These streams
sort the sediment just as
ordinary rivers do. The deposits found today that result from moving water in
glacial streams is called stratified drift.
Some of these deposits are large and are of commercial value. For example,
deltas that formed at the end of glacial streams are quarried for their
well-sorted sands.
4. Swamp deposits:
Lakes and ponds are basins in which water is trapped and cannot flow as it does
in streams. Lakes and ponds slowly fill up with sands and clays brought in by
water and wind, as well as decayed vegetation. Eventually lakes become swamps,
which are mixtures of all these materials with a high water content. During
rainy periods swamps can become temporary ponds.
1.
Aquifer:
Rock or
loose earth material that is highly porous and contains large quantities
of water
underground, which can be pumped.
2.
Groundwater:
Water that
is stored in rock or loose earth materials below Earth’s surface.
3.
Permeability:
The rate
(speed) at which water can move through rock or loose earth materials.
4.
Porosity:
The percent of a rock or earth material that is filled with air or water (the
space between the particles or the space in the cracks)
Ready
to Check Up on the Sleeping Giant?
Now
that you have some background on the geology of the Sleeping Giant, you are
ready to do some real field work! You
should bring a notebook with you for collecting data, a simple calculator, a
ruler and a camera, if possible. Group activity equipment will be provided, but
each group will carry and be responsible for its own equipment. This will
include plastic beakers, sieve sets, and maps.
On
this hike you will investigate a variety of geologic features. Read the outline
and the activities that follow before the hike begins so you have some idea of
what you should be observing and doing as you hike:
1.
How the rock
composition changes as you hike the Gorge Cascades trail
2.
Whether
the sizes of particles in the
sedimentary rocks change with their location in Sleeping Giant State Park
3.
Erosional
and depositional features
of the Gorge Cascades stream:
a.
The
stream’s overall shape
b.
Evidence
(and location of) of sedimentation
c.
Types of
erosional features within and alongside the stream
4.
Particle
size analysis
and comparison of alluvium, ice-contact stratified drift and till deposits in the park.
5.
What kind
of deposit can hold the most water?
6.
What kind
of deposit makes the best well site for water supplies?
7.
Features
of diabase
8.
Looking
for contacts (boundaries) between
rock types
Procedure:
1.
Collect a few sample rocks at the start of your hike. (Do
not use rocks close to the road or the parking lot since they may have come from
another location.)
Describe the rocks (include color and size of particles that make up the rocks)
and identify them by name. Record every significant feature you can see. Follow
this same procedure periodically to note whether the rocks change in any way as
you progress up the trail.
(In
the following table, fill in igneous,
sedimentary or metamorphic
in the Family column. In the Location column record whether the
rock was found in a stream bed, at the bottom of a cliff, etc. When you complete
the table, write the number of each rock on your Sleeping Giant map at the
approximate location it was found. Identify the type of rock (Name) if possible.)
Rocks Identified in Sleeping Giant State Park |
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Name |
Family |
Description (include grain size in mm if the rock is sedimentary) |
Location Found |
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1 |
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2 |
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3 |
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4 |
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5 |
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6 |
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Observation:
Did you hike
over any area(s) where there was an abrupt change from one kind of rock to
another? The boundary between two different kinds of rock is called a contact. If you found a contact, describe its setting and the two
kinds of rock you found in contact with each other. Then mark its location on
your Sleeping Giant map.
Hypothesis
(Include illustrations):
Try to imagine what happened to produce the contact
and explain your hypothesis.
2.
Streams constantly change the land over which they flow. Look
for evidence of any changes this stream has made. Record and illustrate the
features you see. Note that in some cases the stream erodes (removes materials from) its streambed and its banks, and in
other cases the stream deposits
(dumps) materials. Using this stream as a example, try to figure out why
streams sometimes deposit materials, but other times do exactly the opposite.
Explain your hypothesis as thoroughly as you can.
PROBLEM:
Where
is the best spot in Sleeping Giant State Park to drill a well for water? (You
will work in groups for this part of the field trip. Each group will do one
activity. All groups will share results and will participate in a full class
discussion to arrive at a final conclusion on the above question.)
A.
The
alluvium deposits of the Mill River
B.
The
ice-contact stratified drift deposits near the Mill River
C.
The till
deposits on the north side of the park
D.
Swamp
deposits
Use
the surficial map of Mount Carmel to determine where the alluvium, the
stratified drift, the swamp deposits and the till are located. Collect a
small sample of each to use to do one of the following three activities. After
doing these activities, each group will share its results with the class so the
entire class will have access to all the information gathered. Then each group
will reconvene and make a final decision about the best location for a well.
Experiment 1: Design
and perform an experiment to compare the
percent composition (by size of particle) of the following: Alluvium
alongside the Mill River, the ice-contact stratified drift near the Mill River,
the sediment alongside the Gorge Cascade and the swamp sediment. (See Table 1)
Then write a short, but complete lab report detailing your work. The lab report
should include the following components: Problem statement, hypothesis,
procedure, results (with all data collected and any math you did), conclusion,
and validity. Be sure to write the lab report in third person just like a
scientist! Do this on a separate sheet of paper.
In the conclusion of your report, record the percent
composition by sizes measured with the sieve set and indicate which material you
think would make the best aquifer.
Table 1. 
Experiment 2: Design
and perform an experiment to compare the percent
porosities of the alluvium, the ice-contact stratified drift, the swamp
deposits, and the till in Sleeping
Giant State Park. Percent porosity is determined by dividing a total measured volume of
the drift (or till) into the space between the particles of sand, and them
multiplying by 100%. Write a short, but complete lab report detailing all of
your work. The lab report should include the following components: Problem
statement, hypothesis, procedure, results (with all data collected along with
any math you did), conclusion, and validity.
Be sure
to write the lab report in third person just like a scientist would do!
Write your report on a separate sheet of paper. In
your conclusion, discuss whether you think the ice-contact stratified drift or
the till would make a better aquifer.
Experiment 3: Design
and perform an experiment to determine which would be the best location to
collect water easily and quickly: In the alluvium, the ice-contact stratified
drift, the swamp deposits or the till. The rate at which water can move through
earth materials is referred to as permeability. Use the depth-to-bedrock map to
choose a particular site for the well after you have selected the earth material
with the highest permeability.
Write a short, but thorough lab report detailing your
procedure and results. The lab report should include the following components:
Problem statement, hypothesis, procedure, results (with all data collected along
with any math you did), conclusion, and validity.
Be sure to write the lab report in third person just
like a scientist would do!
Write your report on a separate sheet of paper. In
your conclusion discuss the speed with which water could be moved from each of
the three materials tested.
Follow-Up:
Collect information from all three previous experiments to determine which
material would probably make the best well site.
Learning
to recognize basalt and diabase in the field
Basalts,
diabases, and gabbros all contain a significant amount of iron. In the presence
of water the iron combines with oxygen to form iron oxide or rust. So when these
rocks are weathered they lose their dark color and look reddish. Sometimes the
reddish color is the same as the reddish arkose. So how can you tell (without
cracking the rock to look at a fresh surface) if you are walking over bedrock
that is arkose or diabase?
Basalt
and diabase show some unusual features that can be used for identification even
when the rocks have weathered surfaces that do not show the rocks’ real
textures and colors:
1.
Rock in
steep locations weathers and weakens over time; chunks of rock break off, fall
and form a pile at the base of the cliff. Basalts and diabases tend to break off
in the shape of columns with polygonal ends (often pentagons or hexagons). If
you see a pile of columns with several flat sides, you can be reasonably sure
you are looking at basalt or diabase. Diabase talus does not show these shapes
as well as basalts, but still tend to be very angular with straight sides. The
diabase and basalt is also more of an orange-brown color than the arkose, which
is more maroon or reddish.
Figure
2. Sample of
arkose. Notice its reddish color. Basalt and diabase tend to be a more rusty
color. Basalt and diabase are also harder than arkose. Sometimes arkose contains
visible pebbles.
2.
In some
places you can observe polygonal shapes on the surface of basalt and diabase
that represent jointing (cracking) that occurred as the young rock cooled and
contracted. Look for surfaces like this on large pieces of diabase. If you are
lucky to find a good example of a pattern of polygons (like a mosaic) on a
rock’s surface, take a picture of the feature or illustrate it. Indicate where
you found it on your map. (Note: Mudcracks, which form when a very fine-grained sediment in a lake
bed dries out can also look like this. But the rock will then be a dark maroon
or dark gray color, rather than a rusty brown color.)
Figure
3. Column
tops on basalt outcrop. The filling between the columns is more resistant to
weathering than the basalt, so the filling stands out as ridges.