Shortage of volcanic black cinder in Hawaii triggers emergency search

Hawaii has a relatively limitless and growing supply of volcanic rock, yet the availability of one particular kind has triggered an emergency search by state officials.

What’s in short accessible supply is black cinder, the highly porous small hard bits expelled by fountaining lava without much exposure to oxygen before cooling.

This material, known as scoria in geolo­gical terms, is highly valued by Hawaii’s roughly $80 million flower and nursery plant industry along with landscapers, coffee farms and others as a planting medium.

Hawaii’s commercial supply of black cinder, however, is nearing depletion despite no shortage of volcanic cinder cones on the Big Island, where at least 12 cubic kilometers of lava has erupted over the past two centuries.

The situation has prompted the state Department of Land and Natural Resources, at the direction of the Legislature, to pay a research team to find big deposits of black cinder on public or private land that is well suited for commercial excavation on Hawaii island.

Funded by up to $150,000 in federal coronavirus recovery aid, the search was ordered by state lawmakers who passed a bill in 2021 to address the dwindling supply of black cinder, which threatens flower farms, nurseries and other major users.

”We are in an urgent situation,” Douglass Adams, director of the Hawaii County Department of Research and Development, told lawmakers in written testimony on the bill.

Lawmakers had hoped for the study to be done by now, but DLNR recently reported back to the Legislature that it needs more time to arrange for the work to be carried out.

By the end of this month, the University of Hawaii at Hilo’s Geology Department is expected to take on the project under a contract and deliver results by June, while providing research work for students who will gain field experience.

Steve Lundblad, a UH Hilo geology professor, suspects that finding a commercially viable new supply of black cinder may not be easy — despite the abundance of the raw material — due to potential landownership, zoning, access, cultural, environmental, regulatory and cost issues.

“There are plenty of cinder cones (on Hawaii island),” he said. “I don’t think it’s all that difficult to find (a large source of good black cinder), but I think the difficulty is going to be finding something that works given all the regulatory and other constraints.”

If the survey work succeeds in identifying one or more new commercially viable sources of black cinder, it remains uncertain who might begin a potentially expensive and lengthy regulatory process and then operate a new quarry.

According to Eric Tano­uye, president of the Hawaii Floriculture and Nursery Association, using black cinder as a planting medium in Hawaii was popularized in the mid-1960s by his late father, Harold, who demonstrated its superiority to soil and bagasse mulch from processed sugar cane stalks.

The source at the time was from a 1960 eruption in Kapoho that produced many cinder cones.

“There was a boom,” Tanouye said of the use of black cinder as a planting medium statewide with distribution from Kapoho.

The Kapoho supply was exhausted about 10 to 15 years ago, and a subsequent quarry established in Pahoa, where trucking and excavation contractor Sanford’s Service Center mines black cinder from a decades- old volcanic eruption, is no longer producing good material, according to Tanouye, who operates Green Point Nurseries on Hawaii island.

“You’re basically buying the leftovers from that pit,” he said.

Tanouye and several other Hawaii agricultural and landscaping industry operators sought help from the Legislature in 2021 to help find a new commercial source of black cinder because of no known good options.

Cinder is quite common on Hawaii island, according to the U.S. Geological Survey’s Hawaiian Volcano Observatory, but not all cones formed around fountaining lava contain it.

The key to cinder production, HVO explained, is the occurrence of small pieces of fountaining lava that contain a medium amount of gas bubbles and cool significantly before landing on the ground.

Too much gas produces soft pumice, while slower- cooling lava bits stick together as spatter.

The color of cinder also varies, ranging from orange to black depending on how long cinder is exposed to oxygen before cooling to a certain degree.

As a planting medium, reddish cinder has undesirable properties including fine particles, according to Adams of the county’s Department of Research and Development.

A couple of cinder cones were produced during Kilauea’s 2018 eruption in Pahoa, mainly at Fissures 17 and 22 within the Leilani Estates rural housing subdivision, according to HVO. But the dominant fountain in Leilani Estates, Fissure 8, now known as Ahuailaau, is predominantly pumice, while other fissures are mainly surrounded by spatter.

Mauna Kea and Hualalai volcanoes on Hawaii island each have several dozen to 100 cinder cones around their peaks, according to HVO, while Hualalai also has cinder cones along its rift zones. Some cinder cones also exist on Mauna Loa.

State Rep. Greggor Ilagan (D, Pahoa-Kalapana) said all the variables involved in determining whether a new commercially viable black cinder quarry site can be found presented too big of a barrier for private enterprise to take on.

Ilagan led the introduction of 2021’s black cinder survey bill, House Bill 834, and said farmers depending on black cinder especially need help after negative impacts from COVID-19 on Hawaii’s agriculture industry.

“I’m a big supporter for ag,” he said, adding that the federal financial aid being used for the study can be used as economic stimulus for industries that have suffered from coronavirus- related impacts.

Dawn Kitagawa, president of the Hawaii Export Nursery Association, noted in written testimony on the bill that farmers exporting potted plants to the mainland are required by government regulators to use black cinder instead of soil.

“Without a new source of quality black cinder, our foliage industry will become nonexistent,” she said.

Tanouye of Green Point Nurseries added that black cinder has become a signature that plants are from Hawaii.

“Cinder is an icon,” he said.