Lesson 14: Continental Hotspots
This week we'll again explore parklands shaped by hotspot volcanism. This time, however, we'll look at what happens when the mantle plume ascends beneath continental rather than oceanic lithosphere. Linear chains of volcanoes that are older away from the hotspot are found in both settings, but partial melting of "granitic" continental crust means that explosive caldera-forming eruptions of rhyolite magmas are major components of continental hotspot systems. We'll also look at the hydrothermal features (hot springs, geysers, etc.) that develop in continental regions where shallow magma bodies interact with groundwater. Finally, this week we'll begin working on the outlines of our second articles which also focus on hotspot volcanism.
As you read through this chapter and the supporting websites please take careful notes so that you can keep track of major points and recall them more easily when we refer to them later in the semester. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.
Weekly Learning Objectives
Upon successful completion of this week's lesson, a student is expected to be able to:
- Describe how the ages and locations of the Columbia River flood basalts, basalts of the Craters of the Moon volcanic field, rhyolite calderas of the Snake River Plain, and modern volcanism, uplift and hydrothermal activity at Yellowstone National Park are related to the movement of North America across the Yellowstone hotspot.
- Outline five observations which support the interpretation that Yellowstone is currently underlain by exceptionally hot crust and upper mantle rocks atop the Yellowstone plume "tail".
- Identify hot springs, geysers, mudpots, and travertine terraces on the basis of their appearances and behaviors, and briefly explain how each of these hydrothermal features develops and where the materials it erupts or deposits originate.
- Determine whether a valley was likely carved by stream or glacial erosion on the basis of its cross-sectional shape.
- Apply the principle of isostasy to explain why the Yellowstone Plateau (which lies atop the hotspot) is higher and the Snake River Plain (which has moved off the hotspot) is lower than "normal" continental crust that lies north or south of the hotspot track.
Reading and Browsing Assignment
- Read Chapter 9 and focus on the topics covered in the learning objectives above.
- For a rundown of what's currently happening at Yellowstone and a review of some of the recent research that has been done there, check out the Yellowstone Volcano Observatory website.
- To learn more about both the fissure-fed basaltic eruptions that occurred early in the eruptive history of the Yellowstone hotspot and the rhyolite caldera-forming eruptions that occurred later in its history, check out the sections on these topics in Vic Camp's How Volcanoes Work website. (Camp, by the way, has written a terrific paper on how the Columbia River Basalts and Snake River Plain rhyolites are "connected"; here's a link to the abstract.)
- Finally, to learn a little more about the late-stage basaltic volcanism that occurs along the hotspot track in the wake of the rhyolitic calderas browse through this overview of the Geology of Craters of the Moon National Monument. (There's also an in-depth version of this document if you would like to learn more about any specific topic.)
Exercise 14 (Due by 9:00 AM on Monday, 26-Apr-2010)
This week's exercise is to complete the third of our four writing assignments. To review the assignment click on the "Documents" link on the left side of this page, scroll down, and click on "Writing Assignment" near the bottom of the page. This week we'll be completing steps one and two and you'll be turning in the outline of the article you choose from the first set.
- Choose one of the two articles in Set 2 and read that article carefully. You'll find that PDFs of the articles are either linked directly to the Writing Assignment page or are available under "Resources" on the GEOL 14 Etudes site (just click the "Etudes»Resources" link). After you've downloaded and read the article of your choice write down notes on its key observations and conclusions. Don't hestitate to post a note to the discussion board or contact me by private message if you have questions about an unfamiliar term or idea. Finally, write an outline of the article's major conclusions and supporting evidence by following the format of the "sample outline" that's linked to the Writing Assignment page.
- Imagine that you are telling a friend who hasn't read the article what its three or four key conclusions are and what data or observations were presented to support each of them. You want to do your best to focus on the major points of the article and not on minor details. When you write your outline you do not need to copy the sample outline exactly (e.g., same font and bullets), but be sure to include the complete article citation, your PIN (last 5 digits of your Etudes user id), and the course name and date at the top. Also, write your outline in complete sentences (not single words or phrases) and be sure that it is well organized and coherent so that a reader can easily follow the main themes of the article.
- Before you start writing please review your first outline and check out the outline grading rubric that is linked to the Writing Assignment page so that you can see which criteria I will use to evaluate your outline. There is no set length for your outline, but if it's longer than about a page or page and a half it won't be as helpful when you go to write your abstract. (Abstracts are very short, so the more you can winnow the article's main themes from its peripheral details when you prepare your outline, the less work you'll have to do later). Also, if you print a copy of the article be sure to save that copy so that you'll have it to refer to in a couple of weeks when you'll be writing the corresponding abstract.
- When you have completed your outline go to the Etudes site for our class, go to Exercise 14 in the Etudes "Assignments, Tasks, and Tests" tool and submit your outline as an attached file. Outlines are due by 9:00 AM next Monday (26-Apr-2010.) I'm asking you to send it as an attachment rather than pasting it into a text box because this will preserve your formatting. You should send it as an MS Word document or, if you write it in another program, as a Word-compatible file. If you have any problems just let me know. I will return your outline to you by 3-May-2010, and the second part of this assignment, an abstract of the same article, will be due on 10-May-2010.
Quiz 14 (Due by 9:00 AM on Monday, 26-Apr-2010)
After you feel you have mastered the learning outcomes outlined above, please complete Quiz 14 in the Etudes "Assignments, Tasks and Tests" tool. There are ten questions, each worth one point. If you can answer all of them correctly it means that you know your way around the geology of continental hotspots pretty well and are ready to move on to learn about parklands formed in the oldest part of North America—the North American craton—next week.