Mt. Ruapeho is an active composite volcano made of alternating layers of ash and rock. The rock type consists primarily of andesite and boulders that are strewn far and wide across the landscape indicating its prolific activity: it has a significant eruption every few decades with smaller one occurring more frequently with the last one in September 2007. Crater Lake sits in the mouth of the volcano and has a pH of 1 (greater acidity than the acid in stomach) and a temperature of 38◦C. The amount of water in the lake effects how large the resulting lahar will be and allows geologists to map where the lahar will flow. Lahars going down the volcano can attain speeds of 90 km/hr and can create devastating effects. Due to the volcano’s reach into the upper stratosphere, the volcano is often snow-capped and is used as a ski resort. The class hiked up Mt. Ruapeho in ~6 hours and went down the mountain in less then 2 hours thanks to the ability of trash bags to be used as sleds.