Hawaiian volcanoes - Part 7: Recent eruptions

The written history of Hawai’i only exists for roughly 200 years. This is a relatively short time compared to other areas with volcanic activities. The first American missionaries visiting the islands in 1823 started recording eruptions. Reports of earlier eruptions are based on the interpretations of Hawaiian stories. All recent (except one) eruptions have been at Mauna Loa or Kīlauea. On average the two volcanoes tend to erupt every two or three years. This makes them one of the most frequently active volcanoes in the world.

_{Topographic map of the Hawaiian Islands including recent volcanic activity in red.
commons.wikimedia.org}

Eruptions in both volcanoes at the same time has been a rare occasion. Those events are mostly recorded before 1924, in the time when Kīlauea was continuously active. This continuous activity ended in the Explosive Eruption of Kīlauea in May 1924. Then Halema‘uma‘u crater in Kīlauea (the current home of Pele), was the site of more than 50 explosive events during a 2.5-week period. To this day, these have been the most powerful explosions at Kīlauea, throwing blocks around that weighted as much as 14 tons. This explosion was the result of steam. After the eruption of lava flows have emptied the magma conduit, water was able to flow into the, now empty, space. The interaction of water and hot rock then caused fast steam production leading to the explosive eruption.

_{At Kīlauea, when the lava column drops below the water table, groundwater may come into contact with magma or hot rocks, causing violent steam explosions.
volcanoes.usgs.gov}

After 1924 the activity of both volcanoes overlapped only once, in 1984, for one day. Otherwise the volcanoes tend to alternate their activity. Mauna Loa has been active from 1934 to 1952, while Kīlauea was active between 1952 and 1974. Overall Kīlauea has been dominating the eruptive activity on Hawai’i since then.
Mauna Loa only showed two signs of life in recent years, during very short-lived events. The first was in Jul, 1975 and the second one in March 1984.

Since 2010 the Puʻu ʻŌʻō eruption has been active on the east rift zone of Kīlauea. It is the longest lasting and most voluminous rift zone eruption in recorded Hawaiian history and is erupting through large fissures along the rift zone. If you would like to see it in action, on YouTube you can watch videos of Puʻu ʻŌʻō lava flows for hours.

_{Lava fountains erupt along fissures in the first week of the Puʻu ʻŌʻō eruptions.
volcanoes.usgs.gov}

The Halema‘uma‘u crater at the summit of Kīlauea lasted for over a century and has been nearly continuous ever since its big eruption in 1924. In March 2008, opening of a vent in the Halema‘uma‘u Crater created a small explosion. This was the first explosive activity at Kīlauea’s summit since 1924. Pyroclastic debris from the explosion ranging in size up to 1 meter were thrown into the area, also damaging the Halema‘uma‘u visitor overlook. Villages downwind reported a very fine layer of dust on their cars. In September, later that year, molten lava could be overserved inside the crater that emerges during fountain eruptions until today. Halema‘uma‘u’s activity is the longest summit eruption at Kīlauea since 1924.

_{View onto the Halema‘uma‘u crater on the summit of Kīlauea.
volcanoes.usgs.gov}

Thoughts on the Big Picture Geology

The fact that Mauna Loa and Kīlauea alternate in their eruption phases could imply that both volcanoes are fed by the same deep magma source. But currently the data suggests that each volcano is fed by an individual shallow magma chamber. The fact that the geochemistry of both volcanoes differs in element and isotope composition also suggest two distinct sources.
Since 1956 between 85 and 100 million m³ are erupted at Kīlauea each year, which is around 1000 Olympic swimming pools. A very interesting observation is that this is much larger that the estimated average eruption over the entire Hawaiian-Emperor Chain. During its 70 million year life span it has only erupted 15 million m³ on average.
The reasons for both, the difference in geochemical characteristics between the two active volcanoes and the increase in magma production during the last centuries is currently highly debated. My reading has not carried me far enough to summarize the ideas appropriately, so that this discussion has to be part of a future post.

Previous Posts

Hawaiian volcanoes - Part 1: Introduction
Hawaiian volcanoes - Part 2: The Hawaiian Hotspot
Hawaiian volcanoes - Part 3: A growing volcano
Hawaiian volcanoes - Part 4: The Rejuvenation Stage
Hawaiian volcanoes - Part 5: Evolution to Atolls and Seamounts
Hawaiian volcanoes - Part 6: Mythology vs Geology

References

• Tilling, R.I., Heliker, C., and Swanson D.A., (2010). Eruptions of Hawaiian volcanoes - past, present, and future: U.S. Geological Survey General Information Product 117, 63 p.
• Zeilinga de Boer, J. and Sanders, D.T., (2002). Volcanoes in Human History: The Far-reaching Effects of Major Eruptions. Princeton University Press, 295 p.
• https://www.soest.hawaii.edu/GG/HCV/puuoo_history.html
• https://volcanoes.usgs.gov/volcanoes/kilauea/geo_hist_summary.html
• https://en.wikipedia.org/wiki/Olympic-size_swimming_pool