Unit 3 Hazards at Divergent Plate Boundaries

This unit addresses several overarching goals of the InTeGrate program including analyzing geoscience-related grand challenges facing society (impact of natural hazards), developing students' ability to address interdisciplinary problems and use authentic geoscience data, and improving students' geoscientific thinking skills (interpretation of multiple data sets).

Unit 3 Learning Objectives (and areas in the unit where objectives are addressed)

1. Students will interpret data from multiple sources to characterize geologic activity associated with divergent plate boundaries (in prework and formative assessment).
2. Students will compare and contrast divergent plate boundaries on land and on the ocean floor (during class group work, following instructor discussion).
3. Students will be able to explain how geologists use multiple types of data to characterize geologic activity associated with volcanic eruptions (group activity).

Unit 3 is designed for introductory level geology courses, including courses in physical geology and geologic hazards, but is also appropriate for any course studying plate tectonics. Unit 3 introduces students to physical characteristics of divergent plate boundaries and hazards associated with submarine and subaerial processes at several locations. This unit is best used following Units 1-2 and prior to Units 4-6, but can be used in a different order or even on its own. Students are expected to come to the activity with the following background:

• Familiarity with the basic tenets of plate tectonics and the general characteristics of plate boundaries. One suggested activity is Using Google Earth to Explore Plate Tectonics, by Laurel Goodell.
• Completion of the prework assignment (which could be incorporated into class time if a longer time is available).

Unit 3 is designed for a 50-minute class period with an hour-long prework assignment that uses several websites to introduce students to a particular active divergent plate boundary (the Juan de Fuca Ridge). In class, students will work in small groups and use data sheets as handouts (provided) or computers to access data sheets. This unit is suitable for most class sizes if enough data sets are distributed (e.g. one set to each small group). If used for a longer class or lab period, the prework and in-class work can all be completed in one session (internet access required for prework). Please see the "Instructor Stories" pages to learn more about how Unit 3 has been used in different types of classes.

Students begin Unit 3 with the prework, which has students use websites to learn about an active divergent plate boundary (Juan de Fuca Ridge) and answer questions about the plate boundary. The class period is designed to be used with the instructor's guide (see below) and an instructor's PowerPoint file (see below), as follows:

Prework introduces students to the divergent plate boundary unit by exploring the Juan de Fuca Ridge submarine divergent plate boundary (prework for students is below).

Outline of the class period (including slide numbers from instructor's PowerPoint, student handouts and estimated time):

1. Class introduction and prework debrief (slides 1-4 ); 10 min
2. Introduction to divergent plate boundaries on land (slides 5-6); 10 min
3. Group activity to examine divergent plate boundary activity on land (Student Data Tables and Student Data Handout); 15 min
4. Student report/debrief (slides 7-8); 5 min
5. Summative discussion (slides 9-11); 5 min

Materials Provided:

• Prework for students to complete: Unit 3 Prework (Microsoft Word 2007 (.docx) 25kB Apr1 15) (and as PDF (Acrobat (PDF) 64kB Apr1 15)). This assignment should take approximately 20 minutes.
• Instructor's PowerPoint slideshow for the class period is here: Unit 3 Class Guide ppt (PowerPoint 2007 (.pptx) 4.2MB Apr20 15) and as a PDF (Acrobat (PDF) 688kB Apr20 15)
• Student Handouts for group activities (#1 and 3 above):

Student Worksheet (note most students will bring these in their prework): Unit 3 Student Worksheet In class (Microsoft Word 2007 (.docx) 23kB Apr1 15) (or as PDF (Acrobat (PDF) 56kB Apr1 15)) and

Student Geologic Data Sets: Unit 3 Student Data in class (PowerPoint 2007 (.pptx) 7.7MB Apr8 15) (or as PDF (Acrobat (PDF) 2.6MB Mar15 15))

Handouts, instructor notes, class PowerPoint files, and keys are suitable for a 50- or 75-minute class.

The information and discussion for Activities 1, 4, and 5 should be guided with instructor prompts for students to respond, which can be done in class with structured shout-outs, clickers (if appropriately worded), or other forms of organized discussion. Alternatively these items can be done online with a class discussion forum (e.g. in Blackboard).

Students can leave class with Tables 1 and 2 filled in, or those tables can be turned in for grading (Summative Assessment).

To modify this unit in combination with Unit 4 (Risk at Divergent Plate Boundaries) for use in a single two- or three-hour lab period, we recommend assigning the Unit 3 prework as a pre-lab assignment, and then in the lab session doing the Unit 3 classroom activity, followed by the Unit 4 prework as an in-class activity, followed by the Unit 4 classroom activity.

Formative assessment can be completed during group activities (Part 1 and 3) as the instructor circulates through the room, listening to (and prodding) student conversations.

Summative assessment can be completed formally by collecting Tables 1 and 2 (keys to Tables 1 and 2 are in instructor's PowerPoint) or by asking students to write responses to discussion items in Part 5, and can be graded using this

guide -- private instructor-only file

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PDF -- private instructor-only file

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Resources for submarine divergent plate boundaries:

• MOR
• Earthquakes (USGS/Google Earth, some also on WHOI for EPR)
• Submarine volcanism
  • Gas emissions (EPR)
  • Eruption at Juan de Fuca Ridge during 2011 cruise
  • Resources for students to use to familiarize themselves with the Axial eruption, including links to radio broadcasts with Bill Chadwick about having predicted the eruption (before 2014) and finding that it had erupted in April 2011 (discovered when he went to sea in July 2011).
• Other submarine eruption videos (not divergent plate boundaries):
  • W. Mata (2009) (0:50)
  • W. Mata (2009) clip 2 (0:36)
  • SW Pacific (south of Japan, 2006), narrated (5:45)

Resources for the Afar Rift Region:

• Information on the Afar Rift from the Afar Rift Consortium
• Information from the Afar Rift Consortium at the Royal Society Summer Science Exhibition in 2010
• Images from the Leeds Group work in the Dabbahu region

Eruption of Nyiragongo:

• Photovolcanica: Nyiragongo
• D. Tedesco, O. Vaselli, P. Papale, S.A. Carn, M. Voltaggio, G.M. Sawyer, J. Durieux, M. Kasereka, and F. Tassi, "January 2002 volcano-tectonic eruption of Nyiragongo volcano, Democratic Republic of Congo, "Journal of Geophysical Research 112 (2007), doi:10.1029/2006JB004762.
• Vaselli et al. 2003. Acta Vulcanol. 14/15: 123-128.
• Details on region near Lake Kivu to the SW of Nyiragongo; dry gas vents known locally as Mazukus ("evil winds") pose a threat to humans and livestock; Plume from the lava lake was estimated to include 60000 tonnes of sulphur dioxide per day in May 2002, with significant amounts of HF, HCl and carbon dioxide. Vaselli et al. 2006. Chinese J. Geochem. 25 (Suppl.): 71-72.
• Nyiragongo was difficult for volcanologists to reach because of bureaucratic reasons, and political situations (Tazieff, 1994).
• Flows entered Lake Kivu and posed a threat of releasing the CO₂ and CH₄ stored within the lake (IRIS, 2002; Reed, 2002).
• Analagous fatal 1986 lake turnover and CO₂ release at Lake Nyos, and remediation to prevent future occurrences:
  • USGS site with detailed information
  • less technical site
• Santo et al. 2003. Acta Vulcanol. 14/15: 63-66.
• Demant et al. 1994. Bull Volcanol. 56: 47-61.
• Platz et al. 2004. J. Volc. Geotherm. Res. 136: 269-295.
• Historical descriptions of pre-2002 activity have been assembled by Durieux. Acta Vulcanol. 14(1-2), 2003: 137-144.
• Detailed chronology and analysis of 2002 eruption is found in Komorowski et al. 2003. Acta Vulcanol. 14/15: 27-62.

Eruption of Grimsvotn

• K.S. Vogfjörd, S.S. Jakobsdóttir, G.B. Gudmundsson, M.J. Roberts, K. Ágústsson, T. Arason, H. Geirsson, S. Karlsdóttir, S. Hjaltadóttir, U. Ólafsdóttir, B. Thorbjarnardóttir, T. Skaftadóttir, E. Sturkell, E. B. Jónasdóttir, G. Hafsteinsson, H. Sveinbjörnsson, R. Stefánsson and T. V. Jónsson T. 2007," Forecasting and Monitoring a Subglacial Eruption in Iceland," EOS Transactions 86 (2007): 245 and 248.

Resources for making maps of earthquake epicenters

• USGS earthquake site

This site offers several options for investigating earthquakes with which you can generate a list of recent earthquakes, or see them on a map.

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