Transcript Jack`s Rock Sequence PowerPoint

Crater Lake, Oregon
Crater Lake includes cliffs made of
lava flows, bizarre-shaped pumice
deposits and fantastic spires of rock.
Can just looking at these rock
formations tell us what order of
events took place?
Move on to the next page for an
interactive journey into the crater.
Image from:
http://vulcan.wr.usgs.gov/Volcanoes/CraterLake/
Maps/map_crater_lake_topo.html
Crater Lake, Oregon
Click on a field site link. Start with * sites.
(This field experience travels the boat tour counterclockwise around the lake.)
3* 2*
4
To return to
this page,
click on the
location star
on the small
map on each
page.
1a*
1b
5
9
6
7*
8

12
11
10
Back to
intro page.
Site 1a. Welded Tuff and Pumice Layers
Remember: Click
the star to go back.
1. Is it likely these two rock layers formed at the same
time? What evidence supports your answer?
2. Describe a likely sequence of events for these
layers.
Layer A:
welded tuff
(pumice)
Layer B:
welded tuff
(mixed)

Site 1b.
Three Layers

Layer A
Layer B
Layer C
1. Describe the three layers and
try to identify what each
layer is. Remember, this is
the edge of a volcano.
2. Hypothesize how and when
(relative to Layers A & B)
Layer C formed. Describe
your reasoning.
Site 2. Lava Flows
1. How many separate lava flows do you observe?
2. In what sequence did these lava flows take place?
Explain your reasoning.
3. What do you think the lighter material is between the
lava flows?

Site 3. Pumice
1. Was this pumice deposited all at once or over time?
2. What evidence leads you to your conclusion?
See an expanded
view of this site
here.


pumice
back to previous page
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Site 4. Feeder Dikes
Notice the diagonal features circled at this site.
When did these features form in relation to the
horizontal lava flows? Before or after? What is your
reasoning?
Closeup views
are here.
A
B
A
B
back to previous page

Site 5. Devil’s Backbone

Here is a lava feature (a huge one) that cuts across the
horizontal layers. Or is it the other way around?
1. Explain which is older, Devil’s Backbone or the horizontal
layers. Use logical reasoning in your answer.
2. How do you think this feature ended up in the air? Look at
the closeup view. How did it get there? The loose rock on the
slope is a clue.
Closeup view
is here.
Devil’s Backbone
Devil’s
Backbone
Back to
previous
page.
Site 6. Wizard Island
Wizard Island is a volcano (a cinder cone) in a volcano
(mixed shield and composite). Did the two volcanoes
form at the same time or did one form before the other?
If not at the same time, which came first? Use logical
reasoning in your answer.
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Site 7. Lava Flows
1. Notice there are a number of lava flows at this site.
2. In what sequence did these lava flows take place?
Why do you think this?
3. Describe how this mountain formed based on the
evidence at this site.
See a close-up
view of this site
here.

back to last page
Site 8.
The rusty coloring seen in this photo is caused by the
oxidation of iron (like a rusting nail). Do you suppose the
oxidizing occurred when this rock was “recently” exposed
or thousands of years ago when the rock formed? If you
could visit this site, what would you look for to answer the
question?

Site 9. U-Shaped Valley
This U-shaped valley was carved by a glacier.

(Try to picture a glacier filling in the valley.)
Which formed first: the valley carved by the glacier or the crater
from the volcanic explosion? Use logical reasoning in your answer.
Crater rim
Closeup view
is here.
U-shaped valley

Back to previous page.
Site 10. Phantom Ship
1. ?
Emily pics
190 / 162

See the
surrounding
area here.
Phantom Ship
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Site 11.
Layer B (white) appears to be between Layers A and C.
These layers may have formed in the order of A > B >
C, or C > B > A, or Layer B may have been squeezed
or injected between A and C after they formed first.
If you could
visit and look
at these rocks
close up, what
clues would
you look for to
determine their
order of
formation?
A
B
C

Site 12. Pumice Castle
Layers of pumice in a fantastic formation! Did the
pumice form in this castle shape to begin with or did it
become this way after the pumice was deposited?
Describe a process that could cause this feature.
See the surrounding
area here.
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Pumice Castle

Back to previous page.