Historical eruptions on the west side

Most people know about the ongoing eruption at Kilauea, but they don’t realize that Mauna Loa and Hualalai have been quite active. We recently attended a talk by USGS personnel regarding eruptions on the west side of the Big Island that have crossed the road going around the island. Since there is only one road and it is close to the shoreline, volcanic activity that crosses the road  essentially isolates vast portions of the island.

If we ignore the approximately 1801 eruption of Hualalai, all eruptions of which there is a written record have originated on Mauna Loa. That is to be expected since Mauna Loa is second only to Kilauea in frequency of eruptions. As can be seen from the USGS map we are talking about a significant stretch of coastline from South Point to Kiholo Bay on the northern edge of the North Kona District.

If we arrange these eruptions in chronological order we have 1859, 1868, 1887, 1907, 1919, 1926, and 1950.  There were, of course other eruptions but they did not cross the road or went to the eastern side of the island. In order to come from Mauna Loa and cross the road the eruptions have to be quite voluminous and travel rather rapidly. The most voluminous was the 1859 eruption which came from high on Mauna Loa and traveled a distance of about 30 miles to Kiholo Bay in 8 days.

If we consider the time between these eruptions which crossed the road, we come up with 9, 19, 20, 12, 7, and 24 years, which averages out to a significant west side eruption about every 15 years.  There has not been a significant west side eruption since 1950, a period of 64 years. Statistically we are overdue for an eruption on the west side. So the question becomes, not whether there will be a significant eruption on the west side, but when it will occur. Our neighbors know that when they see me hop into the truck and head upslope, it is time for them to go in the opposite direction for the flow is coming.