October 15-17, 2011 - An ash cloud from the Puyehue volcano in Chile causes flight cancellations in Argentina, Brazil, Chile and Uruguay. The volcano has been sporadically active since late May.
May 7, 2013 - In southeastern Luzon, Philippines, the Mayon volcano erupts with ash and rock for about 73 seconds, producing a cloud that reaches 500 meters above the crater, killing five climbers and injuring eight other members of the same party.
Volcanic Explosivity Index (VEI) Proposed in 1982, measures the relative magnitude of an explosive volcanic eruption.
Similar to the Richter Scale, which measures the magnitude of earthquakes.
On a scale of 0-to-8, each whole number represents a tenfold increase of explosivity.
Uses several factors to determine a number, including volume of erupted pyroclastic material (for example, ashfall, pyroclastic flows, and other ejecta), height of eruption column, duration in hours, and qualitative descriptive terms. (USGS)
May 18, 1980 - Mount St. Helens registers a VEI 5 with an erupted volume of approximately 1 km.