Washington officials are helping workers at the 530 Slide scene in Oso, Wash., deal with a variety of environmental hazards created by the disaster.
"Any concerns about the toxicity from the slide are being strictly evaluated and monitored by joint forces working together," Spokeswoman Brielle Nicholas of the Snohomish County Joint Information Center said.
The slide occurred March 22 and killed at least 29 people.
A hazardous materials/environmental group has been established to coordinate efforts at the scene, the Washington Department of Ecology said.
Several dozen 5-gallon propane containers, a few welding tanks and some household hazardous waste materials have been recovered and will be taken away for disposal, the department said.
Many of the homes in the neighborhood had 150- to 250-gallon propane tanks, and one 500-gallon tank was known to be in the area.
"All workers are required to wear protective gear from head to toe, including, but not limited to, proper footwear, pants, jackets, head gear, protective eye wear and gloves," Nicholas said.
Landslides can happen anywhere there is a slope, AccuWeather.com Senior Meteorologist Jim Andrews said.
"It's part of what is called 'mass wasting,'" he said. "Nature lowers the center of gravity. Mountains rise and they fall apart."
The area of the 530 landslide was created through glacial deposits as the Puget Lobe of the Cordilleran ice sheet filled the valley about 10,000 years ago, Andrews said.
"It was carved by north to south flowing ice from Seattle to Bellingham," he said.
The landslide was already present and had a very steep gradient of 500 feet from the top to the bottom. The North Fork of the Stillaguamish River flows through the valley.
"As rivers are wont to do, they will vary their course through a valley like this. It probably was chewing away at the toe of the slide -- an unstable, unconsolidated slide," Andrews said.
Weather has had a huge effect on search efforts.
"The water level has dropped over 2.7 feet since Saturday," Nicholls said. "With the water level dropping, it makes it easier for search efforts to cover more ground -- ground that has not yet been covered. With the combination of the dogs' return, our search team in full swing and the skies giving us a few days of sun, we are anticipating much progress to be made."