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Connection to the
Earth Science Curriculum
Essential Lessons:
Visitors
to Eagle Harbor Light Station will gain an understanding that the rocks and
other materials there serve as a record of the region’s geologic history,
including the role of the mid-continental rift in the formation of the Lake
Superior Syncline.
Earth Science Literacy
Principles-
Big
Idea 2: Earth is 4.6 billion years old.
Big
Idea 4: Earth is continuously changing.
Common misconceptions - Earth has always been the way it
is right now.
- All rocks and planets were
formed at the same time.
- All rocks are more or less the
same.
Michigan
State Science
Content Expectations Addressed: Third Grade:
E.SE.E.2 Surface Changes- The surface of Earth changes. Some changes are due to slow processes, such as erosion and
weathering; and some changes are due to rapid processes, such as landslides, volcanic eruptions, and earthquakes.
E.SE.03.22
Identify and describe natural causes of change in the Earth’s surface
(erosion, glaciers, volcanoes, landslides, and earthquakes).
Sixth Grade:
E.SE.M.4
Rock Formation- Rocks and rock formations bear evidence of the
minerals, materials, temperature/pressure conditions, and forces that
created them.
E
.SE.06.41 Compare and contrast the formation of
rock types (igneous, metamorphic, and sedimentary) and demonstrate the
similarities
E.SE.M.5 Plate Tectonics- The lithospheric plates
of the Earth constantly move, resulting in major geological events,
such as earthquakes, volcanic eruptions, and mountain building.
E.SE.06.51 Explain plate tectonic movement and how the lithospheric plates move centimeters each year.
E.SE.06.52
Demonstrate how major geological events (earthquakes, volcanic
eruptions, mountain building) result from these plate motions.
E.SE.06.53 Describe layers of the Earth as a lithosphere (crust and upper
E.ST.M.4
Geologic Time- Earth processes seen today (erosion, mountain building,
and glacier movement) make possible the measurement of geologic time
through methods such as observing rock sequences and using fossils to
correlate the sequences at various locations.
E
.ST.06.41 Explain
how Earth processes (erosion, mountain building, and glacier movement)
are used for the measurement of geologic time through observing rock
layers.
E
.ST.06.42 Describe how fossils provide important evidence of how life and environmental conditions have changed.
Vocabulary Fresnel lens- A large
lens invented by Augustin-Jean Fresnel which was crafted from smaller lenses. It was lighter, thinner, and flatter than
conventional lenses and made lighthouses visible over greater distances.
syncline-
a fold in rocks,
where younger rocks are found near the center
clinometer / inclinometer – a tool used to measure angles and
slopes
compression
– when a set of
stresses or forces is directed at a rock mass
basalt
– a hard black rock
formed from slowly-cooled magma
basaltic
magma – molten
material from the upper mantle, which cools to form hard, black volcanic rock
conglomerates
– sedimentary rocks
that are formed when larger, round fragments are cemented together to form new
rock
dip
– the measure of the
slope or tilt of rock layers
basaltic
flow tops – the top
layers of lava flows, which are often porous and less dense
flood
basalts – basalts
formed in large eruptions when deep layers of lava spread over great distances
Optional Activity:
Visit the
Lighthouse, Museums and Exhibits
The
lighthouse is open seven days a week in June, September and October from noon
to 5 pm, and in July and August from 10 am to 5 pm. There is a $5.00 admission
fee for adults. Children are free. The admission covers a hosted tour of the
lighthouse, and entrance to the Keweenaw
Shipwreck Museum,
the Commercial Fishing Museum,
and an exhibit of copper mining artifacts.
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Eagle Harbor Lake Shore Traps
Perched at
the northern edge of the Keweenaw Peninsula, this red brick lighthouse
continues to guide ships safely across the harbor and nearby waters of Lake Superior. The
rocky shore near the lighthouse provides visitors with an opportunity to view Lake Shore Traps
and the syncline formed by the Mid-Continental rift found in Lake
Superior’s basin.
Figure 1: Eagle
Harbor Lighthouse and Lake Shore
Traps. Materials Needed for your Visit
The
information provided, GPS, topographic map of the area, a compass, a ruler, and
a homemade clinometer (see directions provided)
Directions:
- Check the battery level in your
GPS and make sure you know how to use it to enter and label waypoints and
navigate to a waypoint.
- Assemble your clinometer.
- Navigate to each of the stops.
- Read the background material and
answer the questions associated with each stop.
Coordinates: N 47°27.525’ W 88°09.549’
The History of Eagle Harbor
Light Station
The
lighthouse was built at Eagle Harbor to help mariners navigate the treacherous
waters of Lake Superior and to mark this rocky point along the Keweenaw Peninsula.
It was first constructed in 1851 as a wooden structure with a Fresnel
lens lit by a sperm oil flame. When the
structure began to crumble under the harsh weather conditions along the shore,
the current lighthouse was constructed next to it. The new lighthouse boasted a two story
keeper’s home and a 44-foot hexagonal light tower with walls 18 inches
thick. The Fresnel lens was replaced by
an aircraft-beacon-type lamp in 1962, and the lighthouse was automated in
1980. It remains operational today and
is visible a full 29 miles from shore.
While the grounds and buildings are maintained by the Keweenaw County Historical
Society, the U.S. Coast Guard is responsible for the routine maintenance of the
light itself (“Eagle Harbor Light Station”, 2011).
Figure 2: Eagle Harbor
Lighthouse.
The Formation of Lake Superior
Lake Superior’s history differs greatly from that
of the other great lakes. About 1.1
billion years ago, the North American continent attempted to break apart along
what became known as the Mid-Continental Rift. This is one of the deepest rifts
in the world (Linder, 2006) and its curving path above Michigan’s
Upper Peninsula helped define the shape of Lake Superior
(Miller, n.d.).
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Figure 3: Lake
Michigan. Satellite
Image.
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Figure 4: Mid-Continent Rift. The
Rift (in orange) extends from Detroit to the Midwest.
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Continental
rifting has occurred repeatedly in the history of the earth. It leads to the formation of ocean basins and
the fracturing of continents. In
essence, the earth’s crust cracks and begins to spread apart.
Figure 5: Continental Drifting. Magma pushes up from the upper mantle as the
two plates spread apart.
A more recent example of this can
be seen in the active East African Rift zone, where the African plate is
breaking apart into two new tectonic plates, the Nubian and Somalian
plates.
Figure 6: East African Rift. This rift is a developing divergent plate
boundary.
As
the crust spread apart in the Mid-Continental Rift, basaltic magma rose to the
surface and cooled. This happened
repeatedly as the rift expanded, erupting layer upon layer of lava on the
surface. In the time between flows,
sediments were deposited on top of these layers. The rifting activity stopped abruptly about 1
billion years ago. As the dense layers
of basalt cooled, they caused the rift valley to sink (Miller, n.d.). Sediments continued to fill this valley. Later, compression (pressure coming from all
sides) of this region caused uplift, forcing the layers of basalt at the edges
of the rift upward until they were almost vertical in some places, forming what
is known as the Lake Superior Syncline.
The rocks on the shore of the Keweenaw Peninsula dip toward the north,
while the rocks on the southern edge of Isle Royale
dip southward, marking the edges of the syncline (Rose, n.d.).
Examining the rocks in either location allows visitors to glimpse some of the
layers of the syncline.
Figure 7: Midcontinent Rift System. Layers of lava pooled
on top of one another, causing the heavy center to sink. Later, compression applied to the region
caused further uplift of the edges, forming what is known as the Lake Superior Syncline.
Lake Shore
Traps
As
the exposed layers of the Lake Superior Syncline have weathered over time, they
have created Lake Shore Traps in some areas.
The word “trap” originated from a Swedish term used to describe stacked
lava flows that have weathered to form a stair-step pattern (St. James, 2010). The traps visible along the shoreline at Eagle Harbor
were formed by the final lava flows of the Mid-Continental Rift which occurred
1087 million years ago, burying the conglomerate under 31 different flows with
a maximum thickness of 600 meters. The resulting layers of flood basalts and
conglomerates of the exposed Lake Superior Syncline have weathered differentially to
form this “stair-step” pattern. Softer
materials, usually the basaltic flow tops have eroded away. These become the bays in the harbor, while
the more resistant rock remains to become points or ridges (Rose, n.d). Some of these
ridges of resistant basalt are visible, but others create submerged reefs in Eagle Harbor
and along the shore
of Lake Superior, which
make navigation in these waters extremely dangerous. The Lake Shore Traps seen along Eagle Harbor
are similar to the famous West Indian Deccan Traps.
Figure 8: Eagle
Harbor Light
Station. The lighthouse is seen here,
along with the Lake Shore Traps that shelter Eagle Harbor
and are responsible for the jagged profile of the coastline.
Figure 9: Lake
Shore Traps. These traps, remnants of the final lava flows
that formed the Lake Superior Syncline, jut out into Lake
Superior making navigation in these areas treacherous.
Tour of Eagle Harbor Lake Shore Traps
Stop 1: N47°27.525’
W88°9.549’ – Northward Dipping Flood Basalts of the Lake
Superior Syncline
Walk along the road here. Several
layers of the flood basalts which comprise the Lake
Superior syncline are visible here. They dip, or tilt, northward into the water due
to the sinking of the dense basalts into the rift zone in the basin of Lake Superior
and because of the compression applied to the syncline.
Logging Q1: Gaze
out into the lake a sketch your general location along the Lake
Superior Syncline. Which
everyday object(s) does the syncline resemble?
Look closely at the rock around you and describe it. What is its color and composition? Is it all basalt, or can you see other rock
types in the layers? Finally, use your clinometer to measure the dip of these layers.
Stop 2: N47°27.321’
W88°9.034 – Lake Shore Traps
Eagle Harbor is sheltered by the trap lavas,
which stretch out like long, thin fingers into the water along the shore. The
more resistant layers of the basalt flows are all that remain. Softer materials have been worn away by waves
and glaciers over time, leaving the bays and pools between the ridges or points
of the traps.
Logging Q2: Look at the
traps along the shore. Can you see any
pattern or alignment among them?
Describe the color and consistency of rock of which they are comprised.
Is it all the same? How do you think
these geological features impacted navigation in the waters in and around Eagle Harbor? Why is the presence of a lighthouse at this
location of vital importance?
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Making and Using your own Clinometer
(Directions
provided by Mark Klawiter)
A clinometer
(also known as an inclinometer) is a tool used to measure the dip (tilt or
slope) of a geological feature. It’s easy and inexpensive to make your own.
Materials Needed:
a protractor with a hole in it, string, and a metal nut
Directions:
Tie one end of the string through the hole in the protractor and the
other end to the nut.
Reading
the clinometer: Hold the clinometer upside down so that the flat end is horizontal
to the ground. This shows a slope of
zero. Notice that the string hangs
straight down, measuring 90 degrees on the protractor. When the slope is zero, your clinometer will show a measurement of 90 degrees. To find the dip of an outcrop, match the
angle of the flat side of the clinometer to the dip
of the rock you want to measure. The
string will hang straight down, pointing to the new measurement on the
protractor. To find the dip, subtract
90 from the new measurement.
Example:
If the clinometer string points to 135
degrees on the protractor, subtract 90 to find the true dip, or 45
degrees.
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Figure 10: Clinometer
Diagram. The weight on the string
causes it to hang straight down.
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Figure 11: Reading the Clinometer. Align the flat base of the protractor with
the rock layers you are measuring to find the dip.
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(This
EarthCache was created after visiting the Eagle Harbor on July
23, 2011.)
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References
Clinometer . (2011). Retrieved August 8, 2011, from
Wikipedia Website: http://en.wikipedia.org/wiki/Clinometer
Compression.
(2011). Retrieved August 8, 2011, from
Wikipedia Website: http://en.wikipedia.org/wiki/Compression_(geology)
Conglomerates,
(2011).
Retrieved August 8, 2011, from Wikipedia Website: http://en.wikipedia.org/wiki/Conglomerate_(geology)
East
African Rift. (2011). Retrieved August 8, 2011, from Wikipedia
Website:http://en.wikipedia.org/wiki/East_African_Rift
Fresnel
lens. (2011). Retrieved August 8, 2011, from Wikipedia
Website: http://en.wikipedia.org/wiki/Fresnel_lens
Keweenaw County historical Society. (2011). Eagle Harbor
Light Station [Brochure]. Eagle harbor, MI: Kordes, M.
Lake Superior. (2011). Retrieved July 29, 2011, from Wikipedia Website:
http://en.wikipedia.org/wiki/Lake_Superior
Linder,
D.O., (2006). Simply superior: The world’s greatest lake. Retrieved July 29,
2011, from: http://law2.umkc.edu/faculty/projects/ftrials/superior/superior.html
Miller,
J. (n.d.). An introduction to the
geology of the north shore. Retrieved July 29, 2011, from: http://www.lakesuperiorstreams.org/understanding/geology.html
Rose, B. (n.d.).
Eagle Harbor. Retrieved July 28, 2011, from: http://www.geo.mtu.edu/~raman/SilverI/MiTEP_ESI-1
Schaetzl, R.J, Darden,
J.T., & Brandt, D.S. (2009).
Michigan geography and geology. New York, NY: Pearson Custom Publishing.
St.
James, J. (2010). Lake shore traps. Retrieved
July 27, 2011 from: http://www1.newark.ohiostate.edu/Professional/OSU/Faculty/jstjohn/UP%20Michigan%20geology/Lake%20of%20the%20Clouds.htm
Images
Aerial of Eagle Harbor
[Photograph].
Retrieved July 30, 2011, from: http://www.geo.mtu.edu/~raman/SilverI/MiTEP_ESI-1/Eagle_Harbor.html
Clinometer [Diagram]. Retrieved July 30, 2011, from: http://www.glf.dfo-mpo.gc.ca/e0005794
Continental Drifting [Diagram]. Retrieved July 31, 2011, from: http://www.igorilla.org/assets/images/where/rifting.gif
Eagle Harbor, MI. [Photograph]. Retrieved July
30, 2011, from: http://www.panoramio.com/photo/11492253?source=wapi&referrer=kh.google.com
Lake Superior [Satellite image]. Retrieved July 30, 2011, from: http://en.wikipedia.org/wiki/Lake_Superior
Lake Superior Syncline [Diagram]. Retrieved July 31, 2011, from: http://en.wikipedia.org/wiki/Midcontinent_Rift_System
Leonard,
K. (n.d.). Eagle Harbor
Lighthouse [Photograph]. Retrieved July 30, 2011, from: http://www.panoramio.com/photo/39496285
Mid-African Rift
[Diagram]. Retrieved August 8, 2011, from: http://en.wikipedia.org/wiki/East_African_Rift
Mid-Continent Rift
[Diagram]. Retrieved July 30, 2011, from: http://www.bitterrootresources.com/i/maps/Mid-Continent-Rift.gif |
