A volcanic eruption sometimes triggers other natural disasters, including floods, landslides, earthquakes and forest fires. The ash in the air affects both humans and animals. While the initial eruption usually releases the pressure of the volcano, lava often continues to flow several years after the eruption.
The ash from the volcano often settles in rivers and streams, forming temporary and unstable dams that cause water levels to increase. If the unstable material breaks free, flooding occurs downstream. The unstable ash also causes landslides, especially during heavy rains. The pressure release affects nearby landforms and may result in shifting of plates to cause earthquakes. Lava is extremely hot, causing ignition of organic materials, including trees. In highly forested areas, forest fires often follow volcanoes.
The ash in the air continues to affect humans in the area. Those with asthma and other pre-existing breathing problems often feel the greatest effects. Ash causes irritation of the skin and eyes. Protective clothing and goggles help to prevent the irritation.
While the eruption often kills nearby plants, volcanic ash is a very rich growth medium. On the rainy side of Hawaii, ferns and small trees begin to grow in volcanic ash about two years after the eruption. However, in areas where moisture is a problem, regrowth can take hundreds of years.