MICHAEL MANGA
EPS 214: Physical Volcanology
Lab 3
In this lab you will examine thin sections from pahoehoe flows from
Kilauea volcano, HI. Sample number 1 is a ``toe'' that erupted
in March 2001; sample number 2 is a cross section across the ropy
surface from the same flow.
Pahoehoe toes forming, HI; photo by J.D. Griggs, USGS web site
Sample number 1 is a complete cross-section of a toe similar to
those shown in this photo
Ropy pahoehoe, HI; photo by T.N. Mattox, USGS web site
Sample number 2 is a cross-section of across the ropy
surface of a flow similar to
those shown in this photo
In both samples it will be quite obvious
that there are two distinct populations of crystals: large ones,
and small ones.
Questions
- What crystals are present in these basalts? Why is the mineralogy
of the two crystal populations so different?
- Does the spatial distribution of the two populations of crystals
vary within the sample?
- How and why does the colour of the glass change within the sample?
- Do the bubble shapes and sizes provide any information?
For example, does their deformation provide information (as they
did in obsidian lavas)? Can you figure out where and when
these bubbles formed?
-
How does the size and number density of small crystals vary with
distance away from the surface of the lava? Why? Try and
answer this question quantitatively.
Last modified 10 February 2002
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