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Archive for October, 2010

Since its the week before the GSA meeting in Denver, I was simply going to skip talking about the field trip I took yesterday with the intro lab.   However, Anne raised the bar by posting a stratigraphic column today of southern Minnesota and two of the units in the local area are now staring me in the face.

Background: the introductory students here are divided into three labs (72 students total, so 24 per lab).   For the first portion of the semester, they do the typical “here’s a mineral, now go and ID a tray of minerals; here’s a rock, now go and ID a tray of rocks” that most beginning geology classes cover.   Once we finish with that segment of lab, we move onto a fairly creative project that involves two lab days driving around the greater St. Peter / Kasota region looking at the sediment & rocks to determine the geological history of the area.   (Disclaimer: I just inherited the lab and get to wonder at its beauty, but don’t have any claim on the format or what we visit.)   Because this is intro, the material is simplified a bit, but the local geology isn’t very complicated to start with.   There are two rock units the students have to identify (the Cambrian Jordan Sandstone and the Ordovician Oneota Dolomite) and two types of Quaternary sediment (glacial till and alluvial deposits).   The students visit all of the units several times at various outcrops around the area, draw contacts on their topographic sheets of the St. Peter quadrangle, and construct an east-west cross-section for the area.

(borrowed from Anne)

Reality: yesterday was the first day of the field trip.   Julie and I drove around a few weeks ago, so that I could visit all ten of the stops (we do 4 on the first day and the remaining 6 on the second day).   When we previewed the trip, the river was still fairly high, but at least all of the roads were open.   Julie gave me a good run-down of what is usually discussed at each stop & about how much time to spend on any given rock in order to return within our 2-hour window.   Yesterday the river was lower, which made examining the alluvium deposits much easier.   However, it was very, very windy, raining / snowing, and fairly darn cold.   I had warned the students about the weather, so they were dressed appropriately (yay!), but it was still a fairly miserable day to be standing out on the side of the road.   (Its also why I don’t have pictures…)   But there were a few golden moments, when I saw lightbulbs actually go off:

  • one student linked the glacial flooding we saw up on the voluntary field trip to Interstate State Park (which I still haven’t posted pictures from…)  to the bedrock terrace found within the dolomite unit
  • another student remembered the depositional environment of carbonates / well-sorted sandstones (what the Jordan sandstone is)
  • several students quickly knew what deposited till
  • I got a few quick teases as a road grader drove by about how it was demonstrating what I was discussing (which was how glaciers move sediment)
  • they managed to ID dolomite, quartz sandstone, granite, and gneiss in the outcrop (the latter are present as erratics)
  • a quick grasp of why the Kasota prairie was never farmed (lots of outcrops of the dolomite–which never would have stopped a New England farmer–that made the Quaternary deposits more appealing for farmers)

The students didn’t complain about the weather.   They enjoyed going out and doing something “different” — a reinforcement of the idea that field trips are the way to go.

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@helenasrox yesterday made a comment about how it was time for geology-related pumpkin carving.   Several years ago, I attended a pumpkin carving party, where I managed to construct a subduction zone on the side of my pumpkin.   Unfortunately, no one is admitting to having pictures (and this was before I had my small camera in my purse at all times).   I commented back & got asked where / why I decided to decorate items with a convergent margin.

While I was at UIowa for my PhD, I TAd for Petrology several years.   During the igneous portion of the class, Tom Foster would go over the various ways that melt is formed & modified at convergent margins.   It would then appear on the 1st midterm exam as an essay / drawing and the students would struggle with the question.   Because of the struggle, it would appear again on the 2nd midterm.   And even though the students knew it was coming (we warned them!), usually >50% of the class would still miss full-credit on the question, so it would make one more appearance on the final.   By the time I went out to Goldschmidt in Idaho in 2004, I had drawn a convergent margin along with the melt processes so often, it was getting to be second nature.   At Goldschmidt, I roomed with several other grad students, all of whom happened to be igneous petrologists.   In the middle of Goldschmidt there was the day free from talks & posters.   The option was to go on the expensive rafting / BBQ trip or go off on your own–we chose the latter and drove up to Coeur d’Alene.   Because it was the end of May, tourists were far & few between around the lake and it was easy for us to get a table at the Italian restaurant.   It was a local place and had the butcher paper on the table along with a tub of crayons.   And we had to wait for our food a bit.   While waiting, we ended up having a discussion about Tom’s melting question and I drew it out on the paper.   But by the end of the meal we had covered the entire piece of butcher paper with all of the tectonic settings that our various rocks came from (subduction zones, hotspots, mid-ocean ridges).   Unfortunately, though I took a picture of the wine bottle on the table, the drawing didn’t get photographed.

wine bottle (and part of the drawing!) in Coeur d'Alaine

Somehow, though, that drawing just cemented in my mind so that whenever I had to draw something, a subduction zone is going to appear.   It happened on the unpictured pumpkin.   Later that same year, I was at a baby shower for another professor in the department and it ended up on a onsie.   Several years later while chatting with that professor at NEGSA, I discovered that that onsie had been a favorite of the family, but they didn’t know who drew it 🙂   (Also no pictures taken… I think I need to take more pictures in the future!)

And, just in case you were wondering, I also ask my petrology students the exact same essay / drawing question 🙂   So, I’m not posting the answer up here where they can find it!

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This week’s geology news was very heavy on events in Chile & Oklahoma:

(Thanks to last week’s commentator’s, I now know how to link directly to specific tweets.)

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We’ve just finished igneous rocks in lecture & lab, but haven’t gotten far enough into metamorphic rocks to really appreciate a paper yet, so this week we’re reading:

Dufek, Josef and Bachmann, Olivier, 2010, Quantum magmatism: Magmatic compositional gaps generated by melt-crystal dynamics: Geology, v. 38, p. 687-690.

(sorry about the paywall…)

The questions I proposed came from where last week’s discussion went (mainly about why the diagrams were important to the paper & what they were trying to convey):

  • what is their data comprised of?
  • how do their interpretations relate back to the data?
  • are all of the diagrams in the paper needed?
  • would you want another diagram or two?

I was tempted to talk about the England & Katz Nature paper, but I thought that the thermal modeling might be a bit too much for the students.   Maybe when we get to subduction zones in the tectonic portion of the class…

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The following is a list of news items that my intro students decided to write about:

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(Papers of the week took a small vacation while my petrology class & I tried to catch up due to a few unplanned pauses, but now we’re back!)

This week’s paper is:

Martin, V.M., Davidson, J., Morgan, D., and Jerram, D.A., 2010, Using the Sr isotope compositions of feldspars and glass to distinguish magma system components and dynamics: Geology, v. 38, p. 539-542.

(Behind a paywall–sorry.)

This paper went into the lineup due to the fact it combined chemistry (topic from week 4) with magma chamber dynamics (week 5 & 6), so its a final review on the information we just dealt with and a preview of what’s coming.   I took the advice of a number of fellow instructors around the web and choose to post several questions that I wanted the students to answer & send me before our discussion this morning:

  • what kind of data is being used by the authors?
  • why did they choose to work with this type of data?
  • identify for each interpretation the data it is specifically based on

The majority of the data is actually in a figure and not within the text, so I’m going to interested to see what the student’s reaction to that is.

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I wrote the last entry, because I really wanted to start recording some of the more unique articles my students found while surfing the internet.   (This week was actually a scatter, instead of having one main repeater.)   So, here’s the week 4 subjects as found by my students:

One student (!) managed to fulfill the extra credit portion of the assignment by finding an article that related to the content of that week’s lecture (week 4: minerals) by finding an article about export of REE elements from China.

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I teach at a liberal arts college that has a focus on integrating writing into as many courses as possible and that does include intro science classes.   The latter can be difficult, especially when I have 70 students and everything has to be graded by me in a timely fashion.   But I understand how important it is, especially in the sciences, to encourage students to write more.   There are some similarities between writing for humanities classes & the sciences (e.g. grammar, well-formulated thoughts, clarity of language), but there are also differences.   In the sciences, there is a strong emphasis on data vs. interpretation, citations to indicate where the facts & information came from, and learning to distinguish between “questionable” and “reputable” sources.

Ok, so how do I do this with 70 intro students?   Several years ago, I was cruising the internet looking at syllabi for other people’s Earthquake & Volcanoes classes.   I was trying to determine what textbooks were being used, which topics had more or less emphasis, and any other special activities that were integrated into the course.   And in this search I found a Middlebury assignment (can’t find the link to it now…), where the students were “journaling” several earthquake/volcano-related news stories a week.   To me, it was a “yes, I have to use this” moment.  The students would get to write something every week, they would have to learn to cite news sources, and they would have a better idea of what was going on geologically in real-time.   Originally, I had the students find two stories per week.   At that point in time I had 80 intro students and it was too much grading.   This semester, I’ve cut back to one entry per week and expanded the topics to anything “geological” that is covered by 2+ public news sources, which is doable grading-wise.   I’m on the fourth cycle of grading and I can already see an increase in their ability to write well, which is thrilling to me.   They will also have a 2-page paper to write later in the semester, but I have hope that the whole process for that paper will be eased because of their continual writing during this semester.

But what do my students find to write about?   I see some definite trends.   The majority end up on one topic (e.g. New Zealand earthquake for the 1st cycle, miners trapped in Chile for the 2nd, local flooding for the 3rd), but a few search far & wide for stranger topics.   In that latter group, I’ve seen articles that were discussed on twitter the week before in either the “yay!” or “fail” category, which is entertaining.   There is also a small group that has discovered that there is an earthquake every week that produces enough news coverage for them to use (e.g. California, Afghanistan, Wyoming).

All in all, I may modify the assignment slightly over time, but I like how it integrates writing into science.

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M&M lab

(Though several people have suggested I try doing this lab with something other than M&Ms (e.g. plastic counters, colored beads), I think its the fact you can actually eat the magma chamber at the end that causes this lab to be a favorite.)

So, what is the process that we’re trying to demonstrate to the students?   Once a melt forms, several things start to happen to the liquid:

  • it rises due to a lower density than the surrounding rock (buoyancy)
  • it interacts with the surrounding rock & starts to cool down
  • in some cases, the surrounding rock melts & adds into the existing liquid (assimilation)
  • sometimes the first melt meets a second melt and they mix together to form some form of intermediate melt (magma mixing)
  • in all cases, the melt cools to a point and starts forming crystals which can either continue reacting with the melt (equilibrium crystallization) or separate themselves chemically from what’s going on in the melt (fractional crystallization), which changes the overall composition of the melt over time
  • in more traditional models of fractional crystallization, the crystals would form & then sink to the bottom of the pool of melt (magma chamber) to collect and each successive layer of crystals would have formed from a later & later point in the melts history
  • how the melt during fractional crystallization changes depends on what the 1st then 2nd then 3rd crystals are made of: if you first take out X from a collection of WXYZ, then the rock will proportionally become more enriched in WYZ & depleted in X; the 2nd mineral removed has a different proportion to pull from, so maybe it takes XY, making WZ be more enriched & XY depleted

For this lab, we’re using the the more traditional sinking model and the M&Ms represent various elements removed to make up a variety of minerals.   The students are given a list of minerals that crystallize out at each stage, so they can figure out how many of each color M&M to move out of the magma chamber.   At the end, you have a “fully crystallized” layered magma chamber:

Mike, Jonathan & Carson's magma chamber

Sam, Andi, & Todd's magma chamber

My students divided into two groups and went about this in very different ways.   The seniors (upper picture) kept all of the “minerals” that crystallized out at every step together, so their colors look mixed together.   The juniors (lower picture) chose instead to group by element, so you can’t see each “mineral” that crystallized, but you have a better idea of how much “Si”, “Al”, or “Fe” was in a given layer.   If you look at the pictures, you should see some trends about how many “crystals” formed at each stage; how the chemical composition changed from layer to layer; and, if you’re really good, how the names of the rocks varied from layer to layer.

There are a few M&M magma chamber activities out there, but I tend to use the more complex version of Wirth’s (intro level also exists).   There are some limitations to what we can model & how the system has to be modified in a delicious candy form, so I tend to follow this lab with the not-as-beloved MELTS lab I adapted from Jim Brophy at Indiana.

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