The worst thing about living near a volcano is the possibility of it erupting, bringing about many negative consequences, such as earthquakes, lava flows, mud flows, flooding, pyroclastic flows, falling ash, carbon dioxide, sulfur dioxide and other toxic gases. In the past, volcanic eruptions have obliterated entire towns and villages and caused great loss of life.
The effect of a volcano's eruption depends on what type it is. Shield volcanoes, such as those in the Hawaiian island chain, cause flows of slow moving lava. These are usually not dangerous to human lives, but damage infrastructure and agriculture. Stratovolcanoes, which are built up from multiple layers of lava, are volatile, highly dangerous and have caused the greatest loss of human life. Subglacial volcanoes cause eruptions beneath glaciers or sheets of ice, and the meltwater can cause catastrophic flooding.
The U.S. Geological Survey has a color-coded system to warn those living close to volcanoes. Green means that the volcano is in its normal, or non-eruptive stage. Yellow warns of signs of background unrest. Orange means that there is significant unrest with likelihood of eruption, or minor eruption activity has begun. Red signals that a major eruption has already commenced or is about to commence. The USGS also has a Volcano Hazards Program to educate people on the dangers of volcanoes and avoid catastrophic consequences in the future.