About This Project

We can't predict eruptions but we can forecast probabilities with enough information. South Sister volcano in Oregon is ranked the 7th highest threat volcano in the US and has been showing signs of magma accumulating ~4 miles below its surface. Yet very little is known about the volcano and the causes of its past eruptions. Therefore, we propose to study the sequence of events leading to South Sister’s past eruptions to help forecast the nature of possible future eruptions.

Ask the Scientists

What is the context of this research?

Over the last 10 to 15 years there’s been a revolution in volcano science. We have learned a great deal about the processes driving volcanic eruptions, including that eruption characteristics such as explosivity and size are statistically related to which magmatic process initiated the eruption. This has led to the insight that by mapping the sequences of processes leading to past eruptions at a given volcano, we can estimate the probability of a given process occurring in the future and what type of eruption it is most likely to produce.

What is the significance of this project?

The US Geological Survey has given South Sister volcano its highest threat ranking and listed it as the 7th highest threat volcano in the US. The volcano has also shown signs of unrest through ground surface uplift and small earthquakes in recent years, which are thought to be caused by an accumulation of magma ~4 miles below the volcano. Simultaneously, South Sister is one of the most poorly understood volcanoes in the western US. While the volcano remains mostly quiet today, understanding the processes that led to its past eruptions is critical to interpreting its current behavior and forecasting its future behavior should the volcano show increasing unrest in the future.

What are the goals of the project?

Erupted lavas and tephras are a combination of quenched liquid magma and crystals that grew as the magma traveled to the surface. We gain insight into a magma’s history from the chemistry of the sample as a whole, as well as zones within individual crystals, which record the temperature, pressure etc. of the magma at different points in time, allowing us to reconstruct a magma’s history. Thus, our goals are to:

1. Collect ~20 lava samples from past eruptions at South Sister

2. Analyze the chemical composition of whole lava samples using X-ray fluorescence & inductively coupled plasma mass spectrometry (ICPMS)

3. Analyze the chemical compositions of individual crystal zones in the lavas using an electron microprobe

4. Map the sequences of processes that produced a given eruption

5. Repeat for as many eruptions as we can afford

6. Calculate probabilistic event trees (if we study 3+ eruptions) following methods in this paper

7. Share our results.