Forms of Volcanic Hazards (AQA A Level Geography) : Revision Note

Although they are all unique, volcanic eruptions have common hazards

• Primary (a direct result of the eruption)

• Secondary (a result of the primary hazards)

Tephra – solid material of varying sizes that is ejected by a volcano – ranges from ash (less than 2mm in diameter) to volcanic bombs (more than 64mm)

Ash fallout – large quantities of ash carried by the wind and deposited on the ground

• It can travel many km, causing respiratory problems, injuries, damage, deaths and disruption to transport

• E.g. the 2010 Eyjafjallajökull eruption in Iceland produced an ash cloud that disrupted air travel in Europe for several weeks

Pyroclastic flow (also known as nuée ardente) - a super-heated mixture of gas and tephra that flows at speeds of up to 700 km per hour

• This is one of the deadliest volcanic hazards as they can travel long distances and destroy everything in their path

• E.g. when Fuego volcano erupted in Guatemala in 2018, pyroclastic flows destroyed several nearby towns

Lava flow – lava flows travel at different speeds depending on slope, temperature and viscosity

• Most move slowly enough that they are not a risk to human life but can cause significant damage to property and infrastructure

• The fastest flows can reach speeds of up to 60 mph

• In the 2021 eruption of Mount Nyiragongo in the Democratic Republic of Congo, lava flows travelled almost 10km destroying properties and killing over 30 people

Volcanic gases – eruptions can release large quantities of gases such as sulphur dioxide and carbon dioxide

• They are hazardous to human health causing respiratory problems and deaths

• E.g. Kilauea in Hawaii (USA) releases large amounts of sulphur dioxide leading to air quality alerts and health warnings for residents

Lahars – mudflows that occur when tephra mixes with water, either from rainfall, or from melted snow and ice

• They are fast flowing and destroy everything in their path

• E.g. the lahars that occurred when Mount Pinatubo erupted in the Philippines in 1991 caused extensive damage and disruption

Jökulhlaups - floods caused by a sudden release of water and rocks when glacial ice is melted by the eruption

• The 2010 eruption of Eyjafjallajökull triggered a jökulhlaup which destroyed several bridges and roads

Acid rain – forms when sulphur dioxide emitted during the eruption reacts with water vapour in the atmosphere to form sulphuric acid

• It can damage crops, forests and aquatic ecosystems