Engage an expert to conduct a volcanic hazard assessment for project area
A volcanic hazard assessment should be carried out to identify which volcanic hazards (e.g. ashfall, gases, ballistic projectiles, lava flows, lahars and pyroclastic density currents) may affect your project location. Volcanoes can produce multiple hazards:
- Pyroclastic density currents (sometimes called pyroclastic flows): these are fast-moving clouds of hot gases and particles, formed by the collapse of an eruption column or the explosive interaction of magma with water (ground or surface). They travel very rapidly, at speeds >350 km/hr, down the sides of the volcano and can extend out to tens of km from the vent. They are highly lethal (from both heat and pressure/impact) and destructive to most structures.
- Lahars (volcanic mudflows): these are flows of volcanic debris-laden water which travel downslope under gravity and thus follow river valleys. They can travel far (100 km or more) from the volcano. It is important to note that lahars can also be triggered during non-eruptive times, e.g., by crater lake breakout events, or by heavy rainfall onto unconsolidated material from previous eruptions.
- Ballistic projectiles: these are fragments of lava or rocks from around the vent of the volcano which are violently ejected from the volcano and follow ballistic trajectories. They may be both lethal and destructive, but are usually limited to within a few km of the vent.
- Ash: Volcanic ash consists of fragments of rock that become airborne during a volcanic eruption. The general term for all such material is ‘tephra’, with ‘ash’ constituting the material less than 2 mm in size. Ash is dispersed downwind, and can be carried hundreds or even thousands of kilometres away from the volcano, and cover large areas of land with ashfalls.
- Gas: Volcanoes can emit gases not only during eruptions, but also between eruptions. Volcanic gases are dispersed downwind and may travel hundreds or even thousands of kilometers. The main gases emitted by volcanoes are water vapour, carbon dioxide and sulphur dioxide. Of these, sulphur dioxide (SO2) has the greatest consequences for people and infrastructure due to its ability to form sulphuric acid droplets.
- Lava flows: outpourings of molten magma from volcanic vents or fissures. They typically move slowly, thus tend to be destructive rather than lethal. Avoidance is generally the best mitigation option, but there are also examples of successful attempts to stall or divert advancing lava flows. It is important to note that these measures usually only buy time to delay the onset of lava inundation.
- Sector collapse: volcanoes are often unstable landforms, and even after long periods of inactivity, may suddenly collapse to produce landslides. This may be more common for volcanoes that are closely linked to tectonic faults; collapse is often triggered by earthquakes or volcanic events. Slopes that have been altered by weathering and/or hydrothermal activity may be more prone to collapse.
- Tsunami can be triggered by volcanic eruptions, usually due to landslides displacing large volumes of water, or when eruptions occur beneath large water bodies. Whilst rare, they account for some of the largest losses of life during volcanic eruptions.
- Volcanic earthquakes and sustained tremor.
For more information about volcanic hazards, refer to: http://volcanoes.usgs.gov/hazards/index.php
A volcanic hazard assessment should use a systematic methodology to evaluate credible hazards and ensure that all relevant hazards are included in the analysis. This should include taking steps to understand the distribution of the multiple hazards that a volcanic eruption may trigger. Refer to any local volcanic hazard maps, if available. The volcanic hazard assessment should consider the following background information:
- Volcanic events rarely produce just a single dangerous hazard. Eruptions usually initiate a complex sequence of events that can produce a wide range of eruption products and hazards.
- These hazards can occur in sequence or simultaneously; travel at speeds ranging from very slow (lava flows) to very fast (pyroclastic density currents); and affect different areas around the volcano.
- Even areas tens to hundreds of kilometres away from a volcano can be affected by volcanic hazards, including volcanic ash and gases, lahars and tsunami.
- Episodes of eruptive activity at individual volcanoes can last from hours to decades, or longer and there can be periods of months or years between phases of activity.
- Volcanic regions often have multiple closely-spaced active volcanoes, which increases the likelihood of a nearby site being affected by volcanic hazards.
- Some volcanic hazards can occur during non-eruptive periods. For instance, lahars can be triggered by heavy rainfall onto unconsolidated material from previous eruptions.
- There is a relationship between the size and frequency of eruptions. Larger eruptions tend to be less frequent but have more major impacts. Smaller eruptions tend to occur more frequently, but with more minor impacts.
- Smaller eruptions may be more difficult to forecast as they have fewer warning signs.
- All active volcanoes have the potential to erupt again, sometimes with very little warning. Some volcanoes have erupted after lying dormant for thousands of years or longer.
Consider whether local site conditions (e.g. topography and prevailing wind direction) could increase the exposure of the project site to volcanic hazards. For instance, projects located in valleys may be subject to lahar hazards, even at distances of >100 km from the volcano.
If the project is in a hazardous zone, collect more specific volcanic hazard data for the exact project location. This could start with performing volcanic hazard modelling for the range of possible volcanic threats to the project site (i.e. develop site-specific volcanic hazard assessment model).
For more information on global volcanic hazards and volcanic hazard assessment, please refer to :
Contact organisations that may have knowledge of volcanic hazards in the area: local governmental civil protection, scientific organisations and indigenous communities.
Volcano Observatories
Some countries with active volcanoes have volcano observatories and/or agencies responsible for monitoring local volcanoes and carrying out hazard assessments – to varying extents. If possible, establish a working relationship with the national or local volcano observatory or agency. If a national or local observatory/agency does not exist contact one of the regional or global organizations.
These organisations typically have responsibility for provision of volcanic hazard information and monitoring of eruptive activity to inform warnings to exposed communities. They usually have a good understanding of the range, extent and intensity of hazards which can be produced by the local active volcanoes. They can also be an excellent point of contact for accessing local volcanic hazard information and local/national emergency management/civil protection information and contacts.
The World Organisation of Volcano Observatories (WOVO) provides a semi-regularly updated list of global volcano observatories, including the volcanoes they monitor and their contact details. This can be accessed at: http://www.wovo.org/observatories/
Utilise traditional knowledge to increase understanding of volcanic risk in project area
Traditional and indigenous knowledge can contribute to understanding volcanic risk, especially when the geological or written history of a volcano is limited. Indigenous communities often have their own understanding and ways of articulating a volcano’s processes. They may also have traditional systems of land use planning and emergency management practices.
Utilise local knowledge to increase resilience of project
Consider contacting local or international staff with experience of working in the project area to understand how they have sought to reduce volcanic risk. Previous or other current projects may have already considered the volcanic hazard assessment and risk management approaches required for this region.
