Volcanoes and Associated Hazards Flashcards
What are the different types of plate boundaries where volcanoes occur?
Destructive (convergent) and constructive (divergent) plate boundaries, as well as hotspots.
What type of volcano is most commonly associated with destructive plate boundaries?
Composite or strato-volcanoes. Stratovolcanoes have relatively steep sides and are more cone-shaped than shield volcanoes. They are formed from viscous, sticky lava that does not flow easily. The lava therefore builds up around the vent forming a volcano with steep sides. Stratovolcanoes are more likely to produce explosive eruptions due to gas building up in the viscous magma.
What type of volcano is typically linked with constructive boundaries?
Shield volcanoes. Shield volcanoes are usually constructed almost entirely of basaltic and/or andesitic lava flows which were very fluid when erupted. They are built by repeated eruptions that occurred intermittently over vast periods of time (up to a million years or longer). Shield volcanoes are much wider than they are tall.
What is a cinder volcano?
A type of volcano commonly found on the flanks of shield and composite volcanoes. Cinder cones are the simplest volcano type. They are characterized by a cone shape, steep slopes, and small size. They are also the most common volcanoes. Cinder cones are formed by the accumulation of ejected igneous rocks called cinders that form the slopes.
What are the three types of magma?
Basaltic, Rhyolitic, and Andesitic.
What is the temperature and silica content of basaltic magma?
Hottest temperature and lowest silica content.
What type of eruptions are associated with basaltic magma?
Less violent eruptions with smaller ash columns.
What is the characteristic of rhyolitic magma?
It is cooler with greater silica content, making it thicker and more viscous.
What type of eruptions does rhyolitic magma produce?
Highly pressurized eruptions.
How does silica concentration affect the explosiveness of eruptions?
Higher silica concentration increases viscosity and traps more gas, leading to more explosive eruptions.
What are the two types of hazards associated with volcanic eruptions?
Primary hazards and secondary hazards.
What are examples of primary hazards from a volcanic eruption?
- Lava * Ash * Gas
What are secondary hazards linked to volcanic eruptions?
Structural collapse of the volcano, including rock avalanches and lahars.
What are the two main types of lava?
Pahoehoe and A’A lava.
How does Pahoehoe lava appear?
Smooth and billowy.
What is the viscosity of A’A lava?
Higher viscosity.
What can cause secondary hazards related to lava flow?
Snow and glacier melt leading to floods.
How high can ash columns from powerful eruptions reach?
Up to 12 kilometres into the atmosphere.
What can ashfall from a volcano cause?
- Asphyxiation * Contaminated water * Collapsing roofs
What gases are emitted by volcanoes?
- Carbon dioxide * Sulfur dioxide * Hydrogen sulfide * Hydrogen halides
What was the significant volcanic gas event at Lake Nyos in Cameroon?
Large volumes of carbon dioxide were released, leading to thousands of deaths.
What are pyroclastic flows?
Superheated gas, pumice, and ash that flow down the volcano’s flank.
What speeds can pyroclastic flows reach?
Several hundred km/hr, commonly between 20-70 km/hr.
What causes rock avalanches during a volcanic eruption?
Lateral blasts due to high pressure in the magma chamber.
What catastrophic event occurred during the Mount St Helens eruption in 1980?
2.3 billion cubic meters of material fell, destroying over 600 km².
What is a lahar?
A mudflow created when water mixes with volcanic ash.
What can trigger lahars?
- Torrential downpours * Snow melt * Dam failure
What tragic event did lahars cause in Colombia in 1985?
The deaths of over 23,000 people in Armero.
