Violent and beautiful, dangerous and seductive, volcanoes around the world are the expression of a restless layer of hot magma beneath Earth's crust. Eons ago when Earth was first transforming into a planet of the Sun volcanic activity was responsible for the creation of the atmosphere and much of Earth's water. Nowadays the powerful explosions that spew clouds of ash and gases into the atmosphere can have a significant effect on climate and weather.

The clouds rise miles up into the atmosphere and are carried around the world by global winds. They filter the sunlight and can reduce temperatures on Earth to such an extent that very cold winters or 'little ice ages' may occur.

Scientists cannot do anything to prevent the volcanic clouds from affecting the weather but, using Earth orbiting satellites, they can monitor volcanic activity, analyze and measure the composition of eruption clouds, and follow their movement around the world.

Satellites keep track of volcanic clouds in several ways: TOMS (the Total Ozone Mapping Spectrometer) detects and locates volcanic cloud data about once a day during daylight; geostationary weather satellites use infra-red detectors and give nearly global coverage every 15 to 60 minutes.

The major practical importance of this satellite remote sensing is in identifying and tracking the movement of the eruption clouds. Such information is commonly used for hazard mitigation. This is of prime importance for air traffic controllers, pilots and their passengers. Airplane pilots need to be aware of the existence of an eruption cloud and need to be advised of its location and the speed and direction of its movement so that they can avoid flying through it. The volcanic dust in the cloud can do serious damage to a plane's engines.

In addition to dust particles, a volcanic cloud typically contains volcanic gases and as it moves around the world it incorporates products from the surrounding atmosphere.

The Stumper Questions:

1. Chemical reactions within a volcanic cloud can create an environmental hazard that causes soil to be depleted of nutrients so that plants die. What do we call this hazard?
2. Which three of the following will not be found in a volcanic cloud that has travelled several hundred miles from its point of origin: Silicate dust, sulfur dioxide (SO₂), hydrogen sulfate (H₂SO₄), hydrogen sulfide (H₂S), superheated steam, carbon dioxide (CO₂), carbon monoxide (CO),