Mauna Loa, the largest active volcano on Earth

We just had a week of intense volcanic emissions, called Vog, that covered the south Kohala Coast. This is the longest stretch of Vog we have had during 18 months of living here.  Actually, the rare occurrence of Vog is one the things we love about the Kohala Coast.  This Vog had a slightly rotten egg smell (caused by Hydrogen sulfide) combined with a “burnt rock” smell, like a ceramic kiln gives off at very high temperatures.  We had smelled rotten eggs a couple of times during our years in Hilo when the nearby Pu’u O'o vent was highly active and the wind was blowing toward Hilo.  But here in South Kohala, we are a long way from the active vents of Kilauea and a rotten egg smell at this distance is surprising.

Mauna Loa, the largest active volcano on Earth, is much closer to us.  The volcano covers half of Hawaii Island and has erupted 33 times since its first documented eruption in 1843. Its most recent eruption was from March 24 to April 15, 1984.  The heavy emissions covering the area appeared to be coming from Mauna Loa, but we assumed that it was just an illusion since Kilauea is behind Mauna Loa, but it got us looking more carefully at the web sites monitoring Mauna Loa.

We noticed tilt data from an instrument on the edge of Mauna Loa’s crater showing an increase over the past month. In early September, 350 earthquakes were detected in a 3-day period just west of Mauna Loa’s summit.  The earthquake swarm was in the same area where earthquakes occurred before Mauna Loa's 1975 and 1984 eruptions.  Steam is visible from a live camera located on the northeast rift zone of Mauna Loa’s Mokuʻāweoweo Caldera and the thermal camera shows the heat in the caldera.

The activity on Mauna Loa is not surprising and a future eruption is expected; the question is which direction lava will flow down the slopes. When Mauna Loa erupted in 1950, lava ran down its southwest side destroying  homes near Kailua-Kona.  When it last erupted in 1984, lava flooded the northeastern side of the mountain and stopped just outside Hilo.  In 2008, a magma bump on the southwestern side of Mauna Loa had risen eight inches in just three years.  At the time researchers speculated that the magma may cause a rip in the southwestern rift causing lava to flow toward the K'au District on the southeastern side of the island. Any direction of flow would endanger one or more communities on Hawaii Island.

Living on Hawaii Island, Mauna Loa is a beautiful sight worth keeping a close eye on.