Where do most active volcanoes occur?
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Where do most active volcanoes occur?
Most active volcanoes occur at or near plate boundaries, with about 75% occurring around the 'Ring of Fire' surrounding the Pacific Ocean.
What type of lava is typically found at constructive margins?
Basaltic lava, which has low gas content, low viscosity and a higher temperature, is typically found at constructive margins.
Define the Volcanic Explosivity Index (VEI).
The Volcanic Explosivity Index (VEI) is a logarithmic scale from 0-8 used to measure the magnitude of a volcanic eruption. The index is based on factors such as the height of the material ejected, the volume of the material and the duration of the eruption.
True or False?
Volcanoes are only found at plate boundaries.
False.
Volcanoes can also be found at hot spots in the middle of plates, like Hawaii in the central Pacific.
What type of eruptions typically occur at destructive margins?
At destructive margins, eruptions tend to be explosive as the magma is forcing its way to the surface, often with andesitic or rhyolitic lava.
What are the characteristics of lava at destructive margins?
Lava at destructive margins typically has:
High gas content.
High viscosity.
Lower temperature.
True or False?
The Volcanic Explosivity Index can be measured directly on a scientific instrument.
False.
The VEI cannot be measured on a scientific instrument but is calculated based on a series of measurements and observations.
What is vulcanicity?
Vulcanicity is volcanic activity focused on constructive and destructive plate margins.
How do eruptions at constructive margins typically differ from those at destructive margins?
Eruptions at constructive margins tend to be small and effusive, while eruptions at destructive margins tend to be explosive.
What are the three main factors used to calculate the Volcanic Explosivity Index?
The three main factors used to calculate the VEI are:
Height of material ejected into the atmosphere.
Volume of material.
Duration of the eruption.
What is tephra?
Tephra is a solid material with a range of sizes that volcanoes eject, from ash (less than 2 mm in diameter) to volcanic bombs (more than 64 mm).
Define pyroclastic flow.
Pyroclastic flow is a super-heated mixture of gas and tephra that flows at speeds of up to 700 km per hour.
True or False?
Lava flows are always too slow to be a risk to human life.
False.
While most lava flows move slowly enough that they are not a risk to human life, the fastest flows can reach speeds of up to 60 mph and can cause significant damage to property and infrastructure.
What is a jökulhlaup?
A jökulhlaup is a flood caused by a sudden release of water and rocks when glacial ice is melted by a volcanic eruption.
What was the main impact of the ash cloud from the 2010 Eyjafjallajökull eruption in Iceland?
The ash cloud from the 2010 Eyjafjallajökull eruption disrupted air travel in Europe for several weeks.
True or False?
Volcanic gases are only hazardous if they come into direct contact with people.
False.
Volcanic gases can be hazardous to human health even at a distance, causing respiratory problems and deaths.
What are the two main categories of volcanic hazards?
The two main categories of volcanic hazards are primary hazards (a direct result of the eruption) and secondary hazards (a result of the primary hazards).
Why are pyroclastic flows considered one of the deadliest volcanic hazards?
Pyroclastic flows are considered one of the deadliest volcanic hazards because they can travel long distances and destroy everything in their path.
How does acid rain form as a result of volcanic activity?
Acid rain forms when sulphur dioxide emitted during the eruption reacts with water vapour in the atmosphere to form sulphuric acid.
What is a lahar?
A lahar is a mudflow that occurs when tephra mixes with water, either from rainfall, or from melted snow and ice.
What type of volcanoes are typically found at constructive plate margins?
Shield volcanoes are typically found at constructive plate margins.
Define stratovolcano.
A stratovolcano is a type of volcano typically found at destructive plate margins, characterised by low frequency, high magnitude eruptions.
Give two signs that scientists look for to predict a volcanic eruption?
Signs scientists look for to predict a volcanic eruption are:
Magma rising.
Ground deformation.
Increased emissions of gases.
Increased seismic activity.
True or False?
All volcanoes erupt with the same frequency and regularity.
False.
Volcanic eruptions occur with varying frequency and regularity, depending on the type of volcano and its location.
What tools do volcanologists use to monitor changes in volcanic activity?
Volcanologists use a range of tools to monitor changes in volcanic activity, including:
GPS.
Tilt meters.
Satellites.
Seismometers.
Gas detection.
What is ground deformation in the context of volcanic activity?
Ground deformation in the context of volcanic activity refers to bulges caused by rising magma.
True or False?
Volcanic eruptions always follow historical patterns.
False.
Volcanic eruptions can occur with few warning signs and do not necessarily follow historical patterns.
What is a volcanologist?
A volcanologist is a scientist who studies volcanoes.
What type of activity do seismometers detect in relation to volcanic eruptions?
Seismometers detect increased seismic activity caused by magma movement, which can be a sign of an impending eruption.
What is the difference between the primary and the secondary impacts of volcanic eruptions?
Primary impacts are the immediate effects of the hazard, such as injuries and deaths, and damage to property and infrastructure. Secondary impacts are the longer-term effects, such as economic losses, social and psychological consequences.
Define hazard mapping.
Hazard mapping is a long-term response to volcanic hazards that involves identifying areas at greatest risk and limiting the activities that can take place there.
What are four categories of responses to volcanic hazards?
The four categories of responses to volcanic hazards are:
Prevention.
Preparedness.
Mitigation.
Adaptation.
True or False?
Short-term responses to volcanic hazards usually happen long before an eruption.
False.
Short-term responses usually happen immediately before, during or after a volcanic eruption.
What was the magnitude of the 2010 Mount Merapi eruption on the Volcanic Explosivity Index?
The 2010 Mount Merapi eruption had a magnitude of VEI 4.
What type of volcano is Mount Merapi?
Mount Merapi is a stratovolcano or composite volcano.
Name two short-term responses to the 2010 Mount Merapi eruption.
Short-term responses to the Mount Merapi eruption included:
Evacuation of over 350 000 people.
Erection of temporary shelters.
Mobilisation of the police and military.
Distribution of emergency aid.
Name a secondary economic impact of volcanic eruptions.
Secondary economic impacts of volcanic eruptions include:
Increased food prices.
Slower economic growth.
Decrease in tourism.
What type of response is the improved evacuation plan in the area around Mount Merapi?
The improved evacuation plan in the area around Mount Merapi is an example of a long-term response.
True or False?
Hazard mapping is a short-term response to the eruption of Mount Merapi.
False.
Hazard mapping is a long-term response to the eruption of Mount Merapi.