(CNN)A climber who had stopped to rest during an expedition on Mount Hood was rescued after falling into a snow-covered volcanic crevice.
Caroline Sundbaum, 32, of Portland, Oregon, was climbing the mountain at around 11,200 feet on Friday when another climber saw her sit down to rest on her pack and then disappear, the Clackamas County Sheriff's Office said in a news release.
Mount Hood is an active volcano, so climbers are used to a rotten egg odor that often comes from hydrogen sulfide that vents through the rocks in areas called fumaroles.
Sundbaum fell 15 feet into a fumarole. The climber who saw Sundbaum disappear sprang to action, first calling 911 and then lowering a rope to get her out even before rescue operations got to their location, according to the sheriff's office release.
According to the Portland Mountain Rescue (PMR), Mount Hood has many small fumaroles, but climbers are most familiar with two in the upper crater, known as Hot Rocks and Devil's Kitchen.
"After heavy snow, the fumaroles can be hidden by a snow blanket. Hot gases from the fumaroles melt the deeper snow and create large cavities hidden under the surface snow. These cavities can range from a few feet to 20 feet high," PMR said in a news release.
"If a climber walks on the roof of these cavities, they can easily break through the surface snow and fall in. That's what happened to the climber."
The PMR said that the fall isn't the only concern. Deadly gases can collect in the fumaroles and even if someone survives the fall if they are left in the hole for too long the air can be fatally hazardous.
Sundbaum escaped with only an injured shoulder. She was saved by the presence of the other climber, because officials say it would have been difficult to locate her otherwise.