ContextAudience: undergraduate- or graduate-level petrology course.
Skills and concepts that students must have mastered: This exercise assumes that the student is already familiar with plotting data in Excel. The student should have some basic knowledge of chemical variation diagrams, and how they work in situations of simple fractionation or binary magma mixing. No prior knowledge of the mineralogy and petrology of basalts is required.
How the activity is situated in the course: This activity could supplement class lectures on basalts or magmatic differentiation.
GoalsContent/concepts goals for this activity: Students who complete this exercise should be able to:
- make useful geochemical plots (Harker diagrams) from geochemical data in an Excel spreadsheet
- interpret geochemical plots to suggest or rule out possible petrogenetic processes
Higher order thinking skills goals for this activity: This exercise requires students to formulate hypothesis based on geochemical data.
Other skills/goals for this activity: Students gain practice in using an Excel program to plot geochemical data, interpreting geochemical plots, and writing answers to open-ended questions. In addition, the act of obtaining and using data from online databases like GEOROC informs the students about the powerful resources that have recently become available to the scientific community via the creation of digital cyberinformatics and cyberinfrastructure. A carefully guided approach of guiding students into these databases, through the various steps required to screen, download, import, and use their data, empowers the students in a tangible, practical way to think and act like scientists.
EvaluationThis activity is formatted as a self-paced exercise where students can check their own answers by clicking on "Show answer" tabs. The exercise could be reformatted as a normal homework assignment without the answers given, and graded by the instuctor using his/her own evaluation scheme.
- In preparing this exercise, I found GEOROC's Kilauea Iki dataset too difficult to obtain, too disorganized, and too fragmentary for students to obtain themselves as a part of the exercise. The GEOROC data used in this exercise were obtained by a geographic query (HAWAIIAN ISLANDS->HAWAII->KILAUEA->PUNA BASALT). The data were then downloaded by checking 'All' under 'Individual Output' in the 'Choose Metadata' section in order to sort the resulting Excel file by 'Location comment' to find and select the samples to those from KILAUEA IKIA LAVA LAKE. (While it is not immediately obvious from the GEOROC website, the 'Location comment' is not included if the data are downloaded in 'Standard Format').
- Because the GEOROC development team in Germany does not have access to USGS Open File Reports, the downloaded Kilauea Iki data excludes Helz's numerous drill core analyses [Helz et al., 1994] that were not published in her journal articles. Because of this gap, it is not possible to create anything resembling a complete composition-depth profile through the lake with the data downloaded from GEOROC. I also found GEOROC's three-column format for date of eruption not very useful for plotting chemical changes during the course of the eruption.
- For the above reasons, I thought it was necessary to compile a spreadsheet of my own that the students could use for this exercise. The resulting spreadsheet is not comprehensive, but it should give the students a flavor for the wealth of data available from the 1959 eruption and the resulting drilling studies of the Kilauea Iki lava lake.