What Was Unusual About the 1986 Disaster Around Lake Nyos

What was unusual about the 1986 disaster around Lake Nyos in Cameroon?

A) a volcanic eruption involved a lateral blast of volcaniclastic debris that no one anticipated
B) pyroclastic flows buried surrounding villages,reminiscent of Pompeii 1,900 years earlier
C) volcanically derived carbon dioxide gas bubbled from the lake and suffocated people and animals nearby
D) a slurry of lava and lake water flowed rapidly outward from the lake and buried surrounding villages