alexa van eaton: and volcanic eruptions do create thunder. but there are also other thunderous components to an explosive eruption. you can have rapid expulsion-- man: ooh, [bleep] alexa van eaton: --and air pressure waves, essentially shock waves that create thunderous sounds. [loud eruption] reporter: perhaps for most people within washington and oregon, the real impact came in the form of choking, volcanic ash. for the folks that were in the ash cloud, really, day turned to night. and ash starts raining out of the sky. even in the cars, your eyes were watering. your throat was burning. volcanic ash is not like fireplace soot. it's pulverized rock fragments that are very, very small. and when you get enough pulverized rock, it can destroy buildings. it ruins roads. it covers crops and can cause famine if there's enough of it. michael poland: ash and airplane engines don't mix well. ash melts at about the temperature that jet engines operate. so if an airplane flies through an ash plume and sucks that ash into the engine, it can melt that ash