HILO, Hawai'i — A new gas vent that broke through the lower east wall of Halema'uma'u Crater this week has abruptly doubled the already elevated levels of sulfur dioxide in the area, with the gas emitted from the crater now at its highest levels since measurements began in 1979.

Sulphur dioxide emissions on Thursday reached 1,800 to 2,000 tonnes per day, far above the 150 to 200 tonnes per day that is typical at the crater. (A tonne is a metric ton.)

Testing along Crater Rim Drive found sulfur dioxide concentrations that were above 40 parts per million, according to the U.S. Geological Survey.

Studies show that 10 to 15 ppm concentrations of sulfur dioxide can be toxic if there is prolonged exposure.

Sulfur dioxide can aggravate pre-existing heart and breathing problems.

Crater Rim Drive from Jaggar Museum to Chain of Craters Road has been closed since Feb. 20, when sulphur dioxide levels rose to a level that posed a potential danger to visitors.

District Ranger Gail Minami-Judd said Crater Rim Drive remains closed but said the park has not imposed any additional restrictions for the time being.

However, she said parks officials "are planning for further closures if needed," particularly if light winds or kona winds allow the emissions to collect at visitor hubs in the park.

Increased emissions are sometimes a sign that an eruption is about to take place, but scientists with the U.S. Geological Survey said that is only a "remote possibility" of that this time. The other telltale signs of an eruption, such as swelling under the surface of the volcano, haven't happened yet.

"We continue to monitor for signs such as inflation and increased earthquake activity at Kilauea summit," according to a statement from the USGS Hawaiian Volcano Observatory.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com.