Hawaii Volcanoes National Park was closed for a second day Wednesday as officials waited for a change in wind direction to blow away sulfur dioxide belching from Kilauea volcano.
National Park Service officials said air conditions had worsened since Tuesday, when 2,000 people were evacuated from the Big Island park.
"This morning, with it being cool and some warmer air on top of it, it has kind of created a pancake effect, so we have some more of the vog lower down," said Michael Larson, the park's incident information officer.
So-called vog, or volcanic fog, forms when sulfur dioxide gas reacts with sunlight, oxygen, dust particles and water in the air. Tiny droplets known as sulfate aerosols are created, along with sulfuric acid and other substances.
Elevated levels of sulfur dioxide gas could cause breathing problems, especially among those with respiratory conditions such as asthma, emphysema and bronchitis.
Officials were optimistic the southeasterly winds would change to the normal northeasterly trade winds on Thursday.
Meanwhile, the Hawaii County Civil Defense warned residents in communities outside the park that conditions could worsen before improving.
Six people spent the night at a Red Cross emergency shelter to avoid the sulfur dioxide fumes, civil defense officials said. A school, Volcano Charter, remained closed Wednesday.
The evacuation included the 42-room Volcano House hotel and the Kilauea Military Camp, a vacation destination for military families. The evacuees were taken to hotels in Hilo.
The volcano, which has been erupting since Jan. 3, 1983, began venting elevated levels of sulfur dioxide from Halemaumau Crater, located atop the volcano, in mid-March.