The GSC’s Steve Grasby and partner combine science and traditional knowledge to find out why
By Allison De Toni
April 6, 2018
The hot springs in Gandll K'in Gwaay.yaay, a small island in the southeast Haida Gwaii archipelago, were some of the hottest in Canada — reaching up to 80°C — until a magnitude 7.7 earthquake struck off the west coast of Haida Gwaii in October 2012.
After the earthquake, the hot springs stopped flowing for about 10 weeks. But in early 2013, some springs started to flow again, although not at the same rate, and new springs emerged, but closer to the shore. The temperatures of the hot springs also dipped, ranging from 25℃ to 60℃.
A recent study by NRCan’s Steve Grasby, a research scientist at the Geological Survey of Canada, and colleague Patrick Bartier, a geomatics coordinator for Gwai Hannas National Park Reserve, looked at why the earthquake caused the springs to go dry and whether it caused permanent harm to their flow. They presented their study at an international conference, and their results will be published in a peer-reviewed science paper.
Surveying the springs
The hot springs on Gandll K'in Gwaay.yaay are likely fed by rainwater falling on the hills of nearby islands. This water is then heated almost 4 km below ground before returning to the surface.
Steve and Patrick visited the island in August 2014 to survey 13 springs. They measured their temperature and flow and recorded the water’s chemical makeup. They also reviewed other studies of GPS data that showed that Gandll K'in Gwaay.yaay and surrounding islands had shifted westward after the earthquake.
The researchers also visited the site in May, June and September 2015, January 2016 and June 2017 to visually observe the changes in the hot springs over time.
Water samples from their initial visit showed that the geochemistry of the springs before and after the earthquake was the same, meaning that the path of the springs or their source didn’t change, just their volume. But why?
The earthquake likely opened up cracks and pores in the rock so the groundwater drained into the recharge area (where water seeps into the ground and refills an aquifer), lowering the water pressure that drives the thermal spring system. If the quake had blocked the channels in the rock, it’s possible the hot springs might not have returned.
Locals provide important piece to the puzzle
As part of their study, Steve and Patrick also talked to local Haida people, who noted that the spring had run dry after previous earthquakes and then began to flow again.
“This oral history is the only documentation of these events and provides a key piece of information to the study, namely that this is a recurrent event,” said Steve.
This traditional knowledge helped the pair focus their conceptual model of the flow system and explain why the hot springs would stop temporarily in response to seismic events.
“Consistent with oral history, we see the spring system returning to flow once again,” said Steve. “Incorporating traditional knowledge into our study saved us from going down some wrong paths and focused our research into the right direction.”