By Laura Zuckerman
(Reuters) - Two people were killed and the home they occupied was destroyed after building-sized boulders crashed down a cliff and crushed the two-story structure outside Zion National Park in southern Utah, officials said on Friday.
The rock slide on Thursday night likely killed the couple instantly, said Dawn Wallace, treasurer of Springdale, Utah, whose police department was leading the response to the disaster and who viewed the wreckage firsthand on Friday.
She said the giant boulders had crushed the home and a detached garage in the community of Rockville.
"You could see a car sticking out from the under the rocks," she said. "It was unbelievable."
Utah Highway Patrol Sergeant Mary Kay Lucas confirmed on Friday that two people had been crushed to death inside their home "when the rocks came down."
Lance Weaver, a geologist with the Utah Geological Survey, said rockslides that damage homes or injure people happen from one to three times a year in Utah, but fatalities are rare.
He said heavy snows and freezing temperatures that hit southern Utah last weekend followed by a rapid thaw likely caused the slide in a high-desert region of cliffs and sedimentary rock formations.
A highly erodible sandstone base supports giant boulders that tower above Rockville and other communities. Frost heave coupled with precipitation turns the sandstone to mud, triggering the mass movement, Weaver said.
"Our concern right now is whether we are going to see other rock falls across southern Utah because of the same conditions that brought about this one," he said.
He said rockslides affecting people or property are likely to climb in the region as more houses crowd into remote areas where such natural events occur.
(Editing by Cynthia Johnston, editing by G Crosse)