Lava Isn't the Only Dangerous Aspect of Volcanoes

Volcanic eruptions can be broadly divided into two types: explosive and nonexplosive. Explosive eruptions occur when magma, which is molten rock in the ground, contains gas. These eruptions are so energetic that the magma is pulverized into small rock particles called volcanic ash.

Explosive eruptions are responsible for the highest number of volcanic-related deaths. These events can distribute volcanic ash hundreds of miles from the volcano, causing billions of dollars in air travel disruption, water supply pollution and damage to power lines, structures and machinery. Krakatoa in the Pacific (1883) and Mount St. Helens in Washington state (1980) are examples of explosive eruptions. While Kilauea's and Mauna Loa's eruptions are typically non-explosive, both volcanoes have had explosive eruptions in the past.

The most dangerous features of explosive eruptions are volcanic ash flows — swift, ground-hugging avalanches of searing-hot gas, ash and rock that destroy everything in their path. Ash flows produced during the A.D. 79 eruption of Mount Vesuvius in Italy entombed the towns of Herculaneum and Pompeii. In 1902, ash flows from the eruption of Mount Pelée on the Caribbean island of Martinique killed more than 29,000 people. An explosive eruption of Kilauea in 1790 killed around 80 people.

Nonexplosive eruptions occur when little to no gas is contained within the magma. These events produce small fire fountains and lava flows, such as those erupting from Kilauea and Mauna Loa.

Nonexplosive eruptions tend to be less deadly than explosive eruptions, but can still cause great disruption and destruction. Eruptions at Hawaiian-style volcanoes can occur at the summit or along the flanks. New eruptions typically begin with the opening of a fissure or long crack that spews molten lava into the air and sometimes forms lava flows.

Lava tends to flow rather slowly. Typically it is easy to outrun a lava flow but impossible to stop or divert it. People can escape, but homes and property are vulnerable.

Both explosive and nonexplosive eruptions release volcanic gases, producing a hazardous blend called volcanic fog or VOG. VOG contains aerosols — fine particles created when sulfur dioxide reacts with moisture in the air. It can cause health problems, damage crops and pollute water supplies. The health department warned residents in November that air quality around Mauna Loa would deteriorate because of hazards like VOG.

These particles have global consequences when eruptions eject them into the stratosphere, where they block sunlight, cooling Earth's climate. This effect can cause widespread crop failure and famine and is responsible for many historic, volcanic-related deaths. For example, the 1815 explosive eruption of Tambora in Indonesia caused 92,000 starvation-related deaths.

Snow-capped volcanoes, such as those in the Cascades and Alaska, can produce mudflows or lahars. These hazards form when ice and snow melt during an eruption, or ash is washed loose from the surface by heavy rain.

Mudflows have tremendous energy and can travel up to 60 miles per hour down river valleys. They can destroy bridges, structures and anything else in their path. A mudflow from the 1985 eruption of Nevado del Ruiz in Colombia killed 25,000 people.

By studying past and current eruptions, volcanologists constantly refine our ability to predict and mitigate the hazards and risk associated with volcanic activity. But people who live within range of volcanic hazards also can minimize their risk.

All residents of these zones should develop household plans for evacuating or sheltering in place and prepare emergency kits with first aid supplies, essential medicines, food and water. Events like the Kilauea eruption are reminders that preparing before natural disasters can make communities more resilient when these events strike.

Brittany Brand is an associate professor of geosciences at Boise State University where she also is the director for the Boise State Hazard and Climate Resilience Institute. Her research focuses on eruption dynamics, sediment transport in volcanic flows and volcanic hazard assessment.

This article is an update of a story first published on The Conversation under a Creative Commons license. You can find the original article here.