Gases build in the thick molten rock, escaping with a blast. In contrast, magma in shield volcanoes has less silica, allowing the easy escape of gas and quieter eruptions. Ash causes engines to stall by clogging air filters and damaging moving parts. In airplanes, ash sucked into an engine will melt and make a glassy coating on turbines, causing them to quit. Wet ash also conducts electricity, causing short circuits and power outages following eruptions.
Clouds of ash can disrupt radio communication by scattering or absorbing signals.
And its weight alone can cause damage. They guessed the hummocks were formed by lava breaking through the Earth s crust, deposits left by glaciers, mudflows or even man-made. Formerly majestic St. Helens had pulled back the curtain and revealed that volcanic peaks are just big piles of crummy, rotten rock. Or they can simply subside without warning and not be followed by an eruption. Volcanologists can use various instruments to measure earthquake activity, minute changes in the ground surface and emissions of heat or gas.