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BREAKING: Deadliest Avalanche in Everest History Kills 12

At least 12 are dead and three are still missing after an avalanche cascaded down a climbing route on Mount Everest early Friday morning.

All of the deceased were Nepalese guides prepping ropes for climbers near Camp 2 on the mountain, according to the Associated Press.

Camp 2 is positioned at 21,000 feet, but the freezing level at the time of the avalanche was just above the base camp, Meteorologist Courtney Spamer said.

"With the freezing level below the avalanche point, it was still freezing where the avalanche occurred so the surface warmth likely did not cause the avalanche in this case," Spamer said.

With the freezing level rising at this time of year, avalanches are more likely during this time period. However, at the time of the avalanche there was some fog in the area but winds were calm.

"Usually what contributes to avalanches are unstable layers of snow, usually a bottom layer that has been melted some and then refrozen with a fresh snowpack coming on top of it," Western Weather Expert Ken Clark said. "Think of the bottom layer being like a teflon pan and the top layer your eggs."

With the official climbing season beginning next month, hundreds of climbers have already gathered at base camp to prepare for the 29,035-foot trek, AP stated. Those at the base camp rushed to help after the avalanche subsided.

As the search continues for the three guides still missing, this event will become the deadliest single avalanche to date. The only other year with more deaths was in 1996 when 15 people died on the mountain, but those deaths were over the course of the entire climbing season, according to Everest In 1996, eight people died in one avalanche event, but the others were spread out through the season.

Every year people die attempting to climb the world's highest mountain, as of May 2013 approximately 240 people in total have died on the mountain, according to the History channel.

Earlier in the year, Nepal announced that dispatch officials and security personnel would be stationed at the base camp throughout the spring climbing season to aid in speeding up rescue operations.