Crater Lake, OregonCrater 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, OregonClick on a field site link. Start with * sites. (This field experience travels the boat tour counterclockwise around the lake.)To return to this page, click on the location star on the small map on each page.4567*89101112Back to intro page.1b1a*2*3*

Site 1a. Welded Tuff and Pumice Layers

Layer A: welded tuff (pumice)Layer B: welded tuff (mixed)Is it likely these two rock layers formed at the same time? What evidence supports your answer?Describe a likely sequence of events for these layers.Remember: Click the star to go back.

Site 1b. Three LayersDescribe the three layers and try to identify what each layer is. Remember, this is the edge of a volcano.Hypothesize how and when (relative to Layers A & B) Layer C formed. Describe your reasoning.Layer ALayer BLayer C

Site 2. Lava Flows

How many separate lava flows do you observe?In what sequence did these lava flows take place? Explain your reasoning.What do you think the lighter material is between the lava flows?

Site 3. PumiceSee an expanded view of this site here.Was this pumice deposited all at once or over time? What evidence leads you to your conclusion?

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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?ABCloseup views are here.

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Site 5. Devils Backbone Explain which is older, Devils Backbone or the horizontal layers. Use logical reasoning in your answer.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.Here is a lava feature (a huge one) that cuts across the horizontal layers. Or is it the other way around?Devils Backbone

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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.

Site 7. Lava FlowsSee a close-up view of this site here.Notice there are a number of lava flows at this site.In what sequence did these lava flows take place? Why do you think this?Describe how this mountain formed based on the evidence at this site.

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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 ValleyThis 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.Closeup view is here.Crater rim

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Site 10. Phantom Ship ?Emily pics 190 / 162See the surrounding area here.

Phantom ShipBack to previous page.

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.ABCIf you could visit and look at these rocks close up, what clues would you look for to determine their order of formation?

Site 12. Pumice CastleLayers 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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