## Comparing the Mauna Ulu and Puu Oo Eruptions (Grades 9-12)

Prior to the ongoing eruption of Kilauea, the most longest-lived and voluminous rift eruption in historic time was at Mauna Ulu from 1969-1974. Activity 10. compares the early episodes of these two eruptions. The line graph shows the cumulative eruption volume for the first 20 episodes of the Puu Oo eruption. A similar graph is shown for Mauna Ulu eruption. The graphs can be used to answer the questions provided in the activity.
1. For the time intervals shown, which eruption produced the greatest volume of lava? Puu Oo.

2. What are the volumes for each eruption? Mauna Ulu erupted 70 million m3. Puu Oo erupted 235 million m3.

3. Calculate the rate of each eruption in m3/month and m3/hr. Eruption rate is volume in m3 per unit of time. Mauna Ulu erupted 70 million m3 in about 7 months for an average eruption rate of 10 million m3/month or about 14,000 m3/hr. Puu Oo erupted 235 million m3 in about 17.5 months for an eruption rate of 13 million m3/month or about 18,000 m3/hr. Swanson (1972) used the three longest eruptions of Kilauea since 1952 to estimate a lava production rate of 9 million m3/month. He considered this estimate to represent the rate of magma supply from the mantle source.

4. Are the actual eruption rates higher or lower than those calculated in question 3? The actual eruption rates are much higher. For example, Puu Oo eruptions were relatively brief compared to the repose periods between eruptions. The calculated rates are averages over a several-month period that includes both eruptions and repose periods.

5. Estimate the total erupted volume of the ongoing eruption of Kilauea Volcano. List all assumptions. Assuming a constant eruption rate of 13 million m3/month for 120 months, the volume of material erupted is about 1.5 billion m3. This also assumes that he eruption rate of the first 20 episodes is representative of the entire eruption.

Click here for a handout for Activity 10.

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