• From the volcano’s interior:
  • Lava flow
  • Lava dome
  • Pyroclastic flow
  • Volcanic bombs
  • Ash fall
  • Gas emissions
  • Plume
• From the volcano’s surface
  • Lahars
• Lava dome collapse

• Tsunami
• Earthquake

Lava flow: The velocity of lava flow is generally slow (m/s to m/day), therefore the population living in the volcano’s vicinity has the possibility of escaping in time. The typical volume of lava flow ranges between 0.01km³ and 10 km³. The extension of the lava depends on the slope, the effusion rate, and the duration of the eruption. Lava flow produces irreversible damage to land, and causes forest fires.

Lava dome & lava dome collapse: Sometimes, before the eruption of an explosive volcano, a lava dome builds up. It can expand at a speed of up to 1 metre per day, and is very unstable. When the amount of gas becomes too elevated, the lava dome explodes, and an eruption occurs (e.g. Mount St. Helens).

Pyroclastic flow: A mixture of hot gas and lava blocks can result in large explosions or lava dome collapses. They can reach a speed of more than 400 km/h and are very dangerous.

Volcanic bombs: Lava fragments that are ejected while viscous (i.e. partially melted) and with a diameter of more than 65 mm. Many acquire rounded aerodynamic shapes during their travel through the air.

Ash fall: The very fine material that derives from the volcanic rock. It is present in nearly all explosive volcanic eruptions. In very energetic, explosive eruptions, tephra (ash) is carried upward into the upper atmosphere, and the finest tephra can be carried by a jet stream for hundreds and thousands of kilometres.

Gas emissions and volcanic plume: Volcanoes eject various gasses into the atmosphere, primarily H₂O, CO₂ and SO₂. These can eventually cause acid rains and pollution of water bodies. Additionally, the eruption column (plume) of hot volcanic ash and gas can be dangerous for air traffic (e.g. Eyjafjallajökull, 2010), as the tolerable ash concentration for an airplane is not well known (an eruptive cloud can take only 5 minutes to reach the flight height of an airplane).

In extreme cases of extended volcanic clouds over long periods of time, climate can also be affected. Temperatures may decrease if the volcanic cloud prevents the Sun from reaching the Earth’s surface.

Lahars (mud or debris flows): Flows formed by the mixture of volcanic particles and water. Debris flows are coarser and less cohesive than mudflows.

Tsunami: The explosion of the Krakatau in 1883 triggered a Tsunami that affected coastal areas in Java and Sumatra (Indonesia).

Earthquakes: Volcanic activity can be associated with seismic activity.