Recognizing volcanic products and processes
Overview: Here, we are going to examine deposits and landforms that occur in volcanic settings.
Specifically, using a virtual field trip to Tenerife, Spain, you will be learning how to recognize various
volcanic products (i.e., explosive volcanic products, specific lava textures, intrusive structures) and the
processes that they represent.
Due: This lab is due at the end of the lab period next week. You will be graded based on the
completeness and accuracy of your answers.
To do: Open up the KML file at http://math.mercyhurst.edu/~nlang/vft/ by clicking on the link. Google
Earth will open up on your computer and you will be automatically flown to Tenerife, Spain, which is one
of the Canary Islands located west of North Africa. Each of the field trip stops are highlighted by a
volcano icon – there are a total of five stops with numerous associated sub-stops. Click on each icon,
examine the photo associated with that stop (clicking on the photo will provide a larger picture) and
read the caption. After visiting each stop, answer the questions below. After visiting all of the stops,
there are some wrap-up questions to start bringing some of what you have observed today together.
1) Stop 1.
1-a:
a) What types of structures can be observed in sub-stop 1-a?
b) Were these pyroclastic deposits emplaced by particles falling from the sky or by material moving
laterally across the ground? How might you be able to tell?
c) How might you tell the difference between pumice pieces and lithics?
1-b:
a) Columnar joints form perpendicular to cooling surfaces. Subsequently, based on the orientation of
this columnar joint (which is the same orientation as all the other columnar joints that comprise this
erosional remnant), what was the orientation of the cooling surface here?
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b) Based on the orientation of that cooling surface, can you make any predictions as to whether this
erosional remnant represents a lava flow or an intrusive body?
1-c:
a) How can you differentiate this lava flow as an a’a flow rather than a pahoehoe flow?
b) This photograph shows two distinct lava flows. From this picture and from the satellite view, how can
you tell the difference between those two flows? Which view shows the boundary between the flows
better?
2) Stop 2.
2-a:
a) Why might a dike intrude along a normal fault?
b) What are some observational tests that you could do (if you were out in the field) to test whether
there really is a dike here?
c) How might one actually identify a fault in the field?
2-b to 2-e:
a) What textures were observed in the lava flow(s)?
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b) Do the occurrences of these structures within a lava flow seem contradictory? Why or why not?
c) Is the same lava flow observed at all of these sub-stops? How can you tell?
d) Is/are the flow(s) observed at these sub-stops older or younger than the taller, dark brown flow
immediately east sub-stop 2-b? How can you tell?
2-f:
a) Assuming that the structures observed at this sub-stop formed inside the Earth,
i) What must have happened for this feature to be seen at the Earth’s surface?
ii) What does that imply about the strength of the material next to it? Is that consistent with what this
second unit represents?
3) Stop 3.
3-a:
a) At this stop you are at the summit of the stratovolcano Teide. Toggle between the photograph view
of the lava flows in the distance and the satellite views of the same flows. What is morphologically
different between these flows and the ones on the flank of Teide (you can observe part of one of Teide’s
flows in the foreground of the 3-a photograph)?
b) Did the lava flows in the distance erupt from a single vent or from a fissure? How can you tell?
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3-b:
a) Again, toggle between the photograph and the satellite view of this lava flow on Teide’s flank. Based
on the morphology that you observe on this flow, make a prediction as to how you think this lava flow
was emplaced?
3-c:
a) What textural term may we apply to this sample?
b) If the phenocrysts in this sample are indeed feldspar, what texture(s) would you expect to find in the
feldspar?
4) Stop 4:
4-a:
a) Why would these flows not be considered pahoehoe flows?
b) These flows traveled downhill leaving relatively narrow deposits, but yet spread out when it reached
the bottom of the volcano. Why might that be the case?
c) Could that factor have been an influence in how far these flows traveled? Why or why not? Hint:
think about the channel in the middle of the flow.
4-b:
a) Note how this flow did not reach the bottom of the hill. What might have prevented it from reaching
the bottom?
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b) How do you differentiate this flow from an a’a flow?
4-c:
a) How continuous are the light colored layers in the caldera wall?
b) Can that observation help make any predictions as to whether those deposits are airfall deposits or
pyroclastic flow deposits?
c) What textures would you expect to see in the dome and why?
4-d:
a) What type of volcanic structure is represented by this picture? How is it differentiated from a
stratovolcano or caldera?
b) What do we call the material erupted out of this type of feature? Be specific.
c) In what direction was the wind likely blowing during this eruption? How can you tell?
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5) Stop 5.
5-a:
a) This photo shows a lava flow on top of a pyroclastic deposit. How can you tell the two deposit types
apart?
b) What is the orientation of any layering you observe in the pyroclastic deposit?
c) Does that imply that this deposit is an airfall or flow deposit?
5-b:
a) What textures can you observe in the deposits here?
b) Was this deposit likely emplaced through airfall or flow? How can you tell?
5-c:
a) What textures can you observe in the deposits here?
b) Was this deposit likely emplaced through airfall or flow? How can you tell?
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Bringing it all together:
1) Based solely on the structures and features that you have observed today, can you make any
predictions as to the compositions of the materials that have erupted here? Explain your answer.
2) We often apply terms of a’a’ and pahoehoe to basaltic lava flows. Can these textural terms be
applied to other compositions as well?
3) Examine the sample shown in stop 3-c. This is a picture of a sample from the top of Teide and
represents one of the youngest erupted units on the island. Compare the color of this sample with the
colors of other erupted products that you have observed today.
a) Can you draw any conclusions regarding the approximate age of a unit and its overall color?
b) Why might this be?
4) In introductory geology, you taught that materials deposited at the surface of the Earth are deposited
at a horizontal fashion. Based on what you have observed at Stop 5, is that strictly the case with
volcanic deposits? Why or why not?
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