There are several hazards that volcanic activity can produce.
Eruption clouds occur when massive quantities of ash are ejected into the atmosphere where it can reach heights of 50,000 feet. Eruption clouds have proven to be very dangerous for aviation jets because the ash can shut down the engines. The ash cloud can also be very hazardous regarding air pollution.
Lahars are volcanic mudflows. Lahars are very dangerous because they do not require a volcanic eruption yet can travel hundreds of miles. All that is required is loose pyroclastic material on the volcano that mixes with precipitation or melting snow.
Lava flows are layers of molten rock that flows over the surface, later cooling and solidifying.
Lava bombs are large chunks of pyroclastic material ejected from a volcano. The larger pyroclastic material is called blocks.
Pyroclastic flows are some of the most dangerous hazards caused by composite volcanoes. Pyroclastic flows are superheated clouds of pyroclastic material (e.g., hot rock and tephra) ranging in size from small rocks to the size of houses that are over 1,000 degrees F traveling down a mountain at speeds up to 100 mph.
Tephra (or volcanic ash) is fine particles of pyroclastic material that can be carried thousands of miles away by prevailing winds. Regions hundreds of miles away could suffer collapsed buildings is the falling ash accumulates enough. Tephra can also cool the entire planet if enough is ejected into the atmosphere.
Poisonous gases such as carbon dioxide, carbon monoxide, and sulfur dioxide can travel down a volcano and asphyxiate (suffocating) wildlife and humans. In 1986, an invisible cloud of carbon dioxide traveled down a volcano in Africa asphyxiating 1,742 people and 3,000 cattle.
There are many benefits to volcanic activity. One of the major benefits is the fact that volcanic activity can create very fertile soil for agriculture. The problem is that many civilizations developed near volcanoes for this reason – with sometimes deadly effects. Volcanic activity can also create many mineral resources such as gold, silver, nickel, copper, and lead. Volcanic rock is often used for landscaping, tile, and cement.
Some of the most amazing landscapes are near volcanoes because volcanic activity builds land creating, breathtaking scenery. So volcanoes are economically vital for many regions because of the recreational activity and tourism they bring.
Finally, a new but essential trend is geothermal power. The heat generated by volcanoes can create electricity to power civilization. Geothermal power is an entirely renewable resource free of pollution and energy dependency on fossil fuels. Iceland – the surface manifestation of the mid-Atlantic ridge – has a goal of powering the entire nation on geothermal energy. Geothermal energy is also being used in California, Kilauea, Hawaii, and now Utah.