Every few months since late last year, a cargo ship filled to the brim with sand has sailed from Canada to Hawaii to deliver a natural resource that seemingly is in abundance throughout these islands surrounded by sandy shores.
The granules, grayish-tan in color, aren't for Isle beaches or golf courses. They're for another important use: construction.
Precious Hawaii sand is disappearing at an alarming rate — not only from beaches, but also from inland ground deposits that for decades have supplied one of the main ingredients in concrete.
Recently, restrictions on removing inland dune sand from Maui have forced one of Hawaii's biggest concrete suppliers, Hawaiian Cement, to regularly import sand from British Columbia. And the state's other main supplier, Ameron Hawaii, may have to do something similar in the near future.
"I think we're looking at the sunset of local sand sources," said Chip Fletcher, a geology and geophysics professor at the University of Hawaii-Manoa. "These are islands, and sand is limited. Much of it is under buildings and roads, so it was only a matter of time before we ran out of easily available supplies."
The Canadian sand imports have increased concrete prices and construction costs, and have made the state more dependent on foreign supplies of a commodity affected by global supply and demand, shipping availability and fuel prices.
Before the 1970s, sand for construction in Hawaii came from the state's beaches and from accessible inland supplies deposited thousands of years ago when sea levels were higher.
As beach sand was placed off limits and more inland sand was covered by development, concrete companies on Oahu turned to crushed volcanic rock. But the angular nature of the so-called "mansand" made concrete more difficult to work with and expensive compared with concrete made from smooth, round sand.
So starting in the 1980s, Maui dune sand became the predominant source for Oahu concrete.
About three years ago, concerns over large numbers of ancient human burial sites in Maui sand led Maui County to commission a study on its inland sand resources. The 2006 study estimated that a five-year supply of readily available dune sand remained on the island — raising the possibility that Maui may exhaust its inland supplies of clean sand to replenish its eroding beaches.
Earlier this year, the Maui Planning Commission said Hawaiian Cement could only continue mining Maui sand provided it didn't export any to Oahu. That's when Hawaiian Cement began sand shipments from Canada.
The University of Hawaii's Fletcher isn't surprised that another previously abundant resource needs to be imported.
"Forty years ago we could feed ourselves," he said. "Sustainability in the Hawaiian Islands has been going into the basement for a long time, and this is another example."