Activity 4
The Mystery of A-Mountain
A field investigation
your hypothesis
Is A-Mountain a volcano?
A-Mountain is made up of volcanic rocks. It’s your job to figure out
whether or not A-Mountain itself is a volcano, and to explain how
A-Mountain formed.
1. Do you think A Mountain is a volcano?
If yes, what kind is it?
If no, then how did A Mountain form?
2. List the types of rocks that you need to find to support your
hypothesis. Next to each rock note (a) the process that forms it,
and (b) ways that you can identify that rock.
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stop number ______
field trip observation sheet
Road cut drawing - the big picture:
Close-up drawing of a rock sample:
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Volcanic rock found at this stop: _________________________________
Rock description (texture, color, density, uniformity - include lots of
details)
5 words to describe the rock to someone who has never seen it before:
Outcrop location (describe the location of the stop so you or someone
else could find it again.)
Rock above (find the place where this rock type ends - what kind of
rock does it become? What does the transition look like?)
Rock below (find the place where this rock type ends - what kind of
rock does it become? What does the transition look like?)
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Layer 1
Layer 2
Layer 3
Layer 4
Layer 4
Layer 3
Quarry
Layer 2
Quarry
Layer 1
a-mountain outcrops
Explain what you see in the A-Mountain rocks, including the rock type, rock description and the volcanic processes that formed each rock.
Explain
How did A-Mountain form?
Now that you’re familiar the A Mountain rocks, explain how
A-Mountain formed.
Sequence of volcanic events
1. List the events that formed A Mountain in the order that they
occurred.
2. How do we know the order of events?
Revisit and revise
Revisit your hypothesis
3. After having seen the rocks at A-Mountain, how do
your observations and conclusions compare to your initial
hypothesis? Do they agree or contradict? Explain.
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Speculate
Put the volcanoes on the map
Now that you’ve determined the processes that formed the
A-Mountain rocks, you can work on finding where the rocks came
from.
? Remember the area of a
circle? The radius is the travel
distance.
Approximate travel distances
of volcanic materials:
✓ Volcanic bombs: 2 miles
✓ Volcanic ash: 75 miles
✓ Pyroclastic flows: 10 miles
✓ Lahars: 50 miles
4. For each volcanic event:
✓ Pick a color for each volcanic even and mark the color in the
chart below.
✓ List the rocks associated wtih each event in the chart.
✓ Using a ruler, a compass, and the map provided, draw
a circle around A-Mountain. The radius is the travel
distance. Use your color code for each event!
✓ Calculate the affected area for each volcanic event
and put your answers in the chart.
✓ Use the map to figure out which cities (those inside the circle)
would be affected by each volcanic event had the cities existed
27 million years ago. Put your answers in the chart
Example: if there were evidence of volcanic bombs at A-Mountain
we would draw a circle with a 2 mile radius around A-Mountain,
showing the region where the volcano that produced them might
have once stood.
✓ Lava flow: 10 miles (distance
decreases if lava is viscous)
Color Code Volcanic event
Associated rocks
Area of activity
Cites affected
5. Is there is volcanic hazard in Tucson today, why or why not?
6. How did A-Mountain get its cone-like shape if it is not a
volcano?
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20
N
0
#
#
#
#
#
A
20
40
A-Mountain
60
80
MARANA
ELOY
100 Miles
#
CASA GRANDE
#
PHOENIX
City limits
A-Mountain and Surrounding Cities
GILA BEND
BUCKEYE
WICKENBURG
#
#
#
A
#
FLORENCE
#
TUCSON
ORO VALLEY
PATAGONIA
NOGALES
#
SAHUARITA
#
GLOBE
KEARNY
#
#
#
#
BISBEE
#
CLIFTON
DOUGLAS
SAFFORD
WILLCOX
#
TOMBSTONE
SIERRA VISTA
#
BENSON
#
#
PIMA
#