Volcano Watch: Quantifying corrosion downwind of Kīlauea

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article is by scientists from Aotearoa, New Zealand: Carol Stewart of Massey University; Zhengwei Li and Anna de Raadt with BRANZ Ltd.; and Graham Leonard with GNS Science.

A team of scientists from Aotearoa New Zealand teamed up with scientists from the Hawaiian Volcano Observatory in December 2022 to carry out a small pilot study of atmospheric corrosion rates on the Island of Hawai‘i.

The purpose was to expand our knowledge base of how metal corrodes in different environments, specifically metal often used as building and roofing material.

We carried out studies in extreme coastal environments — exposed to high rates of marine aerosol deposition — and geothermal environments — exposed to hydrogen sulfide and minor amounts of sulfur dioxide — in New Zealand, but we don’t have access to sites exposed to moderate to high concentrations of sulfur dioxide.

This is of particular interest for future volcanic eruptions in New Zealand, such as an eruption in the Auckland Volcanic Field, which is overlain by the city of Auckland. Study findings will also have applicability to other parts of the world, including in Hawai‘i, downwind of volcanic eruptions.

We mounted specially prepared rectangular metal samples of just less than 6-by-4 inches in size, called coupons, coated with:

• Mild steel, the base material for many steel structures; its corrosion rate is fundamental to estimating the service life of such structures.
• Copper, widely used in power distribution systems.
• Zinc and hot-dip galvanized zinc. Hot-dip galvanized zinc is used to protect steel structures, claddings and fastenings.

This was done at three locations downwind and one upwind of Kaluapele, Kīlauea’s summit crater, with permission from Hawai‘i Volcanoes National Park and landowners.

The coupons were retrieved a year later and returned to the Building Research Association of New Zealand’s corrosion laboratory for analysis.

Corrosion products were removed and then the cleaned coupons weighed to determine their mass losses during the year they were exposed. These results were used to calculate first-year corrosion rates.

That data can be used to assess the resistance of these materials to atmospheric corrosion under the influence of volcanic emissions.

We also classified the corrosivity of each site according to the accepted international classification scheme.

Our results indicate that all sites are classified as “Medium” throughout the study period.

This is similar to inland coastal regions of New Zealand, with moderate exposure to wind-driven marine aerosol and geothermal regions not immediately adjacent to geothermal features such as hot springs and fumaroles.

We note that our study period coincided with a period of mostly low sulfur dioxide emissions from Kīlauea volcano on Hawai’i Island and, thus, we likely underestimate corrosivity at other times with higher emissions.

We were particularly interested in the relatively high corrosion rates of copper and zinc at Site 1, which was the closest to Kīlauea’s summit vent but upwind relative to the prevailing trade wind field.

Our previous work in the Rotorua geothermal field suggested that copper in particular is highly susceptible to relatively low concentrations of hydrogen sulfide and sulfur dioxide.

Potential explanations include the presence of hydrogen sulfide at Site 1, and the influence of other environmental factors such as the higher rainfall at this site.

We thank Hawaiian Volcano Observatory and the landowners who hosted the corrosion test rigs, as well as everyone who supported and expressed interest in this study.

We will continue to share new findings and insights and welcome expressions of interest from any parties wanting to progress this work.

That could include areas such as understanding the variability of atmospheric corrosivity around the Island of Hawai’i, assessing corrosivity rates during heightened activity of Kīlauea and/or assessing the durability of materials commonly used for buildings and construction on the island.

Volcano Activity Updates

Kīlauea is not erupting. Its Volcano Alert Level is at Advisory.

During the past week, earthquake rates beneath Kīlauea summit and upper-to-middle East Rift Zone were about double that of the previous week. About 10 earthquakes were located beneath the summit and about 70 in the upper-to-middle East Rift Zone.

Ground deformation rates continue to show slow inflation at the summit and near the Sept. 15-20 middle East Rift Zone eruption site.

Future intrusive episodes and eruptions could occur with continued magma supply.

Mauna Loa is not erupting. Its Volcano Alert Level is at Normal.

Three earthquakes were reported felt in the Hawaiian Islands during the past week:

• A magnitude-1.7 earthquake 8 miles east-northeast of Hōnaunau-Nāpōʻopoʻo at a depth of 6 miles Nov. 15 at 9:26 p.m.
• A magnitude-4.1 earthquake 11 miles southeast of Pāhala at a depth of 20 miles Nov. 14 at 12:42 p.m.
• A magnitude-3.2 earthquake north of Volcano at a depth of 17 miles Nov. 14 at 6:09 a.m.

Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa volcanoes.

Visit the volcano observatory’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.