2. What are the main hazards generated by volcanic activity Flashcards
(18 cards)
What are the two main types of volcanic eruptions?
Explosive eruptions – high-viscosity magma; at destructive (convergent) boundaries.
Effusive eruptions – low-viscosity magma; at constructive (divergent) boundaries.
What are the key features of explosive eruptions?
Occur at destructive boundaries
Viscous, silica-rich magma
Stratovolcanoes formed
Common hazards: pyroclastic flows, ash, lava bombs, lahars
What are the key features of effusive eruptions?
Occur at constructive boundaries
Runny, basaltic magma
Shield volcanoes formed
Hazards mainly from lava flows
What are hotspot volcanoes and where are they found?
Volcanoes formed away from plate boundaries, over mantle plumes.
E.g. Hawaiian chain, East African Rift Valley
What is the VEI and what does it measure?
The Volcanic Explosivity Index (VEI) measures eruption size (volume of material), plume height, and duration.
Scale from 0 (non-explosive) to 8 (supervolcano).
What are the size and shape differences between types of volcanoes?
Shield volcano: wide base, low height, gentle slopes (effusive)
Stratovolcano: steep slopes, layered lava/ash (explosive)
Supervolcano: massive calderas, VEI 8, e.g. Yellowstone
What are the main hazards generated by volcanic eruptions?
Lava flows
Pyroclastic flows
Ash and tephra fall
Gas emissions (e.g. CO₂, SO₂)
Lahars
Flooding from ice melt
Tsunamis (if eruption displaces water)
What are pyroclastic flows and why are they dangerous?
Fast-moving clouds of hot gas, ash, and rock (up to 700°C, >100 km/h)
Destroy everything in their path
Deadliest volcanic hazard
What are lahars and how do they form?
Mudflows of volcanic ash and debris, mixed with water (rain or melted ice).
Can be triggered long after eruption
Fast, dense, and destructive
How do gas emissions pose a threat during eruptions?
Volcanoes release gases like CO₂, SO₂, and HCl
CO₂ can suffocate (heavier than air)
SO₂ forms acid rain
What are the impacts of ash fall and tephra?
Covers land, roofs, roads, farmland
Disrupts aviation
Can cause roof collapse and water contamination
What volcanic hazard can cause tsunamis?
Explosive eruptions that displace large volumes of water, especially during submarine or island eruptions
Volcanic landslides can also trigger tsunamis
What type of volcano is Mt Etna and what is its usual VEI?
A stratovolcano with Strombolian basaltic eruptions. Its typical VEI is 1–2.
What tectonic plates interact at Mt Etna?
The African plate is subducting beneath the Eurasian plate at a convergent (destructive) boundary.
What are some key impacts from Mt Etna’s eruptions?
Lava flows, ashfall, seismic activity, landslides, forest fires, and disruption to transport (e.g. closure of Catania airport).
What tectonic plates interact at Mt Merapi?
The Indo-Australian plate subducts beneath the Eurasian plate at a destructive boundary.
What type of volcano is Mt Merapi and what is its usual VEI?
A highly active stratovolcano with explosive eruptions. Its typical VEI is 2–3.
What are some key impacts from Mt Merapi’s eruptions?
Pyroclastic flows, lava bombs, lahars, ash fall, acid rain, and severe ash-lahar flows during monsoons.
