Flashes of lightning, flames, and the sound from the eruption can be detected from far away. The famous 1883 explosion of the island of Krakatoa in Indonesia was heard in Australia, about 2,400 miles (3,800 kilometers) away, 4 hours later!
The shape of land can change dramatically in a volcanic eruption. When Krakatoa exploded, an island disappeared.
Before it exploded, the volcano’s cone rose about 6,000 feet (1,800 meters) above sea level. Afterward, there was a basin in the ocean floor 4 miles (6 kilometers) across and two-thirds of a mile (one kilometer) deep.
The volcano had caved in because the underlying material was gone, blown away as a huge volume of dust and ash. Eventually the erupting volcano built up a small island again, 2,667 feet (813 meters) high.
Tidal waves can result from volcanic eruption, destroying land and people. The 120-foot (36-meter) wave produced by Krakatoa’s explosion hit the islands of Sumatra and Java, killing some 36,000 people.
Volcanic activity can also create earthquakes, avalanches, landslides, and mudslides.