ES 10
HW 4 - Stratigraphy and the ``History of Rocks''
Due 21 February 1997

Please write your answers on separate paper from this handout. Please staple your pages together, or at least be sure to sign every page with your name, so that I can grade your homework.

You will find that Chapters 9 and 10 of Understanding Earth and the notes to Lecture 12 are useful for this entire homework assignment.

If you have problems with or questions about the homework, please come see me in my office hours or send me an e-mail. My e-mail address is, and my office hours are MW 2:10-3:30 pm in 1539 Galbraith Hall.


Let's assume you are a field geologist, hiking around with your notebook, compass, hammer, and backpack. You are trying to make a unified stratigraphic column from the various outcrops you have seen around you. You need to figure out how to stack the various rock layers in the outcrops so that they are in chronological order, with the oldest rocks on the bottom (remember the principle of superposition?). Fortunately, some of the same rock layers are seen in more than one outcrop. Unfortunately, sometimes there are unconformities, and you need to try to work around them.

Question 1 (4 points)

You have looked at three outcrops today, and you have sketched them in your notebook (see the figure labeled ``Figures for Question 1'' below), using rectangles to represent the rock layers, with different layers having different fill patterns. You have arbitrarily labeled the rock layers A-J, carefully noting that the labels do not necessarily correspond to the correct chronological order.

You're back at camp now, drinking a cool beer, and you are going to assemble the stratigraphic column. Write down the chronological order for the rock layers, with the oldest rock layer first. That is all you need to write down -- just the order of the rock layers. If you decide that some of the layers are the same rock (just with different labels), write down both labels with a slash (``/'') between them, like ``A/B''.

Your answer should look something like: I, J, G, D/E, F, A, C, B, H. Note that this order is probably not the right one.

Question 2 (6 points)

It has been another long day in the field, and you have been looking at more rock outcrops, and making more notebook sketches (see the figure labeled ``Figures for Question 2'' below). Again, you have labeled the rock layers arbitrarily (A-K).

You have also noted that there is an unconformity between layers ``A'' and ``B''.

It is again evening in camp, and you are trying to make sense of the order of rocks you have seen. Again, you are to write down the correct chronological order for the rock layers, just as in Question 1.

Stratigraphy and the ``History of Rocks''

The next three problems are more challenging. Here, you need to examine the sketches in your notebook and use the principles of structual geology (re-read your notes from Lecture 12) to unravel the complex history of the structures you have seen.

When you are asked to write down the geologic history of a region, what does that mean? It means you need to list all the important geologic events which you can deduce from the rock section you have. Some of the things you might have to list are the order in which rock layers were laid down, when intrusions or extrusive volcanics were made relative to the other events in the history, when layers were eroded or folded or faulted, etc. Have a look at figure 9.10 in your textbook -- it does a good job of explaining how to unravel geologic histories.

Question 3 (10 points)

Today, you and the field crew have been exploring a river canyon. High up in the wall of one side of the canyon, you have seen (and sketched) what is shown below in the ``Figure for Question 3'' (surprise, surprise). Here, the big ``plus signs'' are one rock layer, the circles are another, and the filled squares are a third (you've labeled them A, B, and C). There's also a really nice granitic body.

You need to write down (in chronological order) the geologic history of the region. You don't need to be long-winded. A simple list like

  1. First, this happened
  2. Next, this happened
  3. And then this happened
  4. Finally, this happened
is fine!

Question 4 (10 points)

You are again doing the same sort of work. Look at the ``Figure for Question 4'' (shown below) and write down the geologic history of the area. Again, just a simple list (as in Question 3) is all you need to do -- don't spend too much time being long-winded.

Question 5 (20 points)

This time, things are really complicated -- in fact, you're beginning to suspect your instructor of being a pretty sick individual! After a lot of work, you have sketched in your notebook the ``Figure for Question 5'' shown below. Here, there are rock layers going in all sorts of directions, a fault, and some sort of granitic intrusion (which you have called layer B).

Again, you need to write down the geologic history of the region. However, you've also been asked to answer the following two questions:

  1. What kind of a fault is shown in your sketch?
  2. Is the granitic intrusion a dike or a sill?

Extra Credit Problem!!! (50 points of extra homework credit!)
Due 28 February 1997

Yes, this problem is due on the 28th, while the rest of HW 4 is due on the 21st of February. I am giving you one extra week to do the extra credit assignment.

First off, note that this is an extra credit problem -- as such, it is completely optional. You can only help your grade, not hurt your grade, by doing this problem, and if you choose not to do this problem, you won't be penalized. Keep that in mind: this is optional.

You may have heard of the new movie which is out called ``Dante's Peak.'' It involves a volcanic eruption at a fictional Cascade volcano called (not surprisingly) ``Dante's Peak''. (The movie was actually filmed in Wallace, Idaho.)

Your mission, should you choose to accept it (wait a minute -- that's another movie) is to go see ``Dante's Peak'' and write a brief review of the movie. Now, I'm not particularly interested in the film aspects like how the plot went -- it's your basic disaster flick plot, as near as I can tell -- or how the special effects looked. What I am interested in is seeing how you think the movie reflects scientific, social, and political reality.

Some specific questions you should consider (and you might need to re-read your notes from Hubert Staudigel's lecture and Chapter 5 of the textbook) and answer:

  1. What sorts of social and political factors are to be considered when a dormant (sleeping) volcano might be getting ready to erupt again?
  2. Do you feel that the movie did a good job of explaining or portraying these factors? Why or why not?
  3. Several different kinds of volcanic and volcano-related phenomena are portrayed in the movie. Name five of them.
  4. If lava is erupted from the volcano, what kind is it (a'a or pahoehoe)?
  5. What is a phreatic eruption?
  6. What is a pyroclastic flow?
  7. How many dead squirrels do the kids find, and does the dog live?
Please staple your movie ticket to your movie review.

Now, a little info: ``Dante's Peak'' shows at the AMC 12 theaters in the Ralph's shopping center at Villa La Jolla and Nobel and at the AMC 20 theaters in Mission Valley. You'll have to call to get the times. As a student, you can get a discount if you show your ID (and often if you don't...).

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Greg Anderson
Thu Feb 13 20:26:42 PST 1997