# Magnetic anomalies and superplumes: is there a connection?

#### Summary

What causes magnetic anomalies? Is there a relationship between superplumes and changes in polarity on the magnetic time scale?

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## Context

#### Skills and concepts that students must have mastered

Interpret magnetic anomaly data
Understand the hotly debated concept of a superplume

#### How the activity is situated in the course

as part of a sequence of exercises aimed at synthesizing a variety of datasets (and generating & testing hypotheses)

## Goals

#### Content/concepts goals for this activity

makConstruct a data-supported argument for whether or not superplumes can affect the geodynamo, and predict what that would look like in magnetic anomaly data

#### Higher order thinking skills goals for this activity

analyze figures
make observations
formulate hypotheses
test hypotheses
construct summary figures

#### Other skills goals for this activity

working in groups
synthesis of multiple datasets

## Description and Teaching Materials

This exercise progresses from discussing convection in the outer core, superplumes in the mantle and large igneous provinces (LIPs) at the surface to evaluate if there is a relationship among these processes. We use the magnetic time scale to link these datasets together.

For homework, students read Glatzmeier and Olson, 2005 – Probing the Geodynamo (Scientific American).

In groups of 2-3, students summarize how the geodynamo works and why the Earth's magnetic field is thought to reverse polarity, according to Glatzmeier and Olson (2005)

Students then work in groups to make observations about the magnetic time scale. What are some general trends? How long are typical reversals? Does this vary? Why are there no reversals during most of the Cretaceous?

Each group is then given either Figure 1a or 1b from Courtillot et al. (2003). They make observations and write down questions they have. If the class is large enough for multiple groups working on these figures, they combine and summarize key observations. Next, students present their findings to the other group(s). As a class, we discuss the relationships between these two figures and hypothesize about how superplumes might be expected to be manifest at the surface.

Then we plot up the volume of igneous material produced by each LIP (y-axis) versus time (x-axis). Students then examine the magnetic time scale again.

They break into small groups again to discuss whether or not there is a relationship among these datasets. They are given 15 minutes to 1) conduct any additional research (using scientific articles—Wikipedia is verboten) and 2) formulate an argument about the datasets which they then present to the class.

We conclude class by discussing what additional data students would like to consult and if there are multiple interpretations. We also discuss the limits of their ability to test their hypotheses and what steps scientists are taking to better understand these processes.

Courtillot, V., Davaille, A., Besse, J., and Stock, J., 2003, Three distinct types of hotspots in the Earth's mantle: Earth and Planetary Science Letters, v. 205, no. 3-4, p. 295-308.
Glatzmeier, G. E., and Olson, P., 2005, Probing the geodynamo: Scientific American, v. 292, no. 4, p. 32-39.

## Assessment

On a midterm or a final, I ask them to discuss the hypothesized link between superplumes and magnetic anomalies.