The ash produced during a volcanic eruption can cover the entire landscape for miles around a volcano and may affect neighbouring islands. Close to the volcano, accumulated ash can be thick enough to collapse buildings.

Read more: Ashfall

Erupting volcanoes can erupt hot rocks into the air. These hot rocks, which are called blocks and bombs, travel like cannonballs and usually land within 2km of the volcano's vent or dome but can travel as far as 5km or even further, if the eruption is very powerful and explosive.

A debris avalanche is a sudden and rapid movement of rock due to gravity usually resulting from a collapse of the side of a volcano.

Lahars, which are relatively common in the Belham River Valley, are dense, concrete-like mudflows made of volcanic ash and rock. They form when water, especially during heavy rainfall, mixes with and mobilizes the ash and rock on the volcano's slopes. The volcano does not need to be erupting for lahars to form and so lahars can be expected to occur at any time regardless of the volcano's activity.

Read more: Lahars or Mudflows

Lava in the Eastern Caribbean is usually very thick and rarely flows far from the volcano vent. As lava is emitted it accumulates around the vent creating a lava dome. While the volcano is erupting, these lava domes may eventually collapse and trigger pyroclastic flows.

Read more: Lava Flows and Domes

Powerful lightning displays can occur during a volcanic eruption as a result of ash, pieces of rocks, steam, and gases knocking and rubbing against each other in the eruption cloud. Lightning that reaches the ground around volcanoes poses a threat to life and property.

These are hot, fast moving mixtures of ash, rock fragments and gas, flowing from a collapsed eruption column or lava dome.  Pyroclastic flows travel down valleys and completely devastate the area over which they flow. Pyroclastic surges cause greater devastation since they may also sweep across ridges and hills. Pyroclastic flows and surges have caused most of the destruction in Montserrat during the Soufriere Hills Volcano eruption.

Read more: Pyroclastic Flows & Surges

Tsunamis are sea waves, which can be generated by various events including large earthquakes or underwater volcanic eruptions. The impact of objects on the sea surface such as pyroclastic flows, landslides and debris flows may also trigger tsunamis. These waves travel extremely fast - approximately 800km/hr in deep oceans - and can completely cover low-lying coastal areas.

Magma travels through the solid rocks of the Earth's crust to reach the surface. It often has to force its way through, breaking rocks as it goes. This generates small earthquakes which are called "volcanic earthquakes". Volcanic earthquakes usually indicate that a quiet volcano is becoming restless.

Gases such as sulphur dioxide (SO2) and hydrogen sulfide (H2S) are present in poisonous amounts close to the vent or dome of an erupting volcano. Further away from the vent, these gases can dissolve in the atmosphere's clouds to produce an acid rain or mist, which affects human and animal eyes and respiratory systems. These gases corrode metal-building materials as well. Carbon dioxide (CO2) is not poisonous, but it is perhaps the most dangerous volcanic gas. It is heavier than air and gathers in hollows in the ground (like valleys and basins). Since it is colourless, odourless and tasteless, people do not know it is there and can suffocate. In the past, several people have been killed in this way at the Boiling Lake in Dominica.