Scientists uncover billions of gallons of hidden fresh water off Hawai'i
Despite being surrounded by water, island communities like Hawaii rely on collecting freshwater stored in the ground for drinking, irrigation, and commercial industries. But Hawaii's water is at serious risk — climate-driven droughts are making groundwater scarce. The solution to Hawaii's problem may lie in the islands' unique geology. Using a new technique that relies on tracing electrical resistance, a team of geohydrologists has discovered a never-before-seen way the islands' volcanic soil collects and hides away freshwater beneath the ocean's salty surface. Accessing this freshwater could give Hawai'i and other volcanic islands a more sustainable and future-proof solution to collecting water during times of need.
The new study was published Wednesday in the journal Science Advances. A fresh hypothesis — The researchers behind the discovery started their detection work after re-examining existing calculations of the expected versus the measured freshwater on the island — there was a 40 percent or so discrepancy in the amount that should be there, as opposed to the amount that seemed to be there. This begged the question: Where was all the missing freshwater? Traditional geohydrological studies focus mainly on sources of freshwater found floating on the surface of seawater, and may miss water hidden in porous rock layers, like basalt, the researchers say. To figure out where the leftover 40 percent of freshwater was hiding, the team decided to expand their search criteria and focus their attention beneath the salty ocean, using a new kind of imaging technique to reveal what lurked in the rock below the surface.
In search of freshwater — Instead of boring into the rocky seafloor in search of this freshwater, the team used a less invasive method called marine controlled-source electromagnetic imaging to measure changes in electrical resistance in the waters near the islands' shore. Electrical resistance changes dramatically between salty water versus freshwater. To take the measurements, the team released torpedo-like imaging systems off the back of their boat into the ocean near the shoreline. Diving just under the ocean's surface, the imagers pinged electromagnetic signals to detect the salinity of the water hidden in the rock. The study's first author and postdoctoral geophysics researcher at the University of Hawai'i, Eric Attias, said in a video accompanying the research that this process is much like performing an MRI scan on the brain. The measurements reveal where all that missing water has been hiding — and then some. The researchers found massive freshwater reservoirs sandwiched between layers of ocean water-laden basalt. In total, the researchers estimate these reservoirs contain a whopping 920 billion gallons of freshwater.
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