Unusually high, and potentially toxic, levels of sulfur dioxide have prompted the closure of a popular drive at Hawaii Volcanoes National Park.

While the gas is always present at the summit of Kilauea in an area adjacent to Halema‘uma‘u crater, trade winds normally disperse the gas, according to park officials.

But during the past month levels as high as 10 ppm have occurred in a narrow band south/southwest of Halema‘uma‘u. Studies indicate that 10 to 15 ppm concentrations of sulfur dioxide is a threshold of toxicity for prolonged human exposure. Exposure to sulfur dioxide can aggravate pre-existing heart and breathing problems such as asthma, park officials say.

In response to the elevated SO2 levels, Superintendent Cindy Orlando has issued the following orders:

* Crater Rim Drive between Jaggar Museum south/southeast to Chain of Craters Road is closed to all visitor activity, including driving, hiking, and bicycling until further notice due to high SO2 levels.

* Crater Rim Trail from Jaggar Museum parking lot south/southeast to Chain of Craters Road is closed.

* All trails leading to Halema`uma`u crater are closed including those from Byron Ledge, 'Iliahi (Sandalwood) Trail, and Ka'u Desert Trail.

* The park has postponed all work projects in the affected area.

The closures, signed and marked by traffic cones, will remain in effect until SO2 levels return to normal.