Week 5 Flashcards
Volcanoes
- Normally found on plate boundary
- Very destructive
Good Side of Volcanoes
- Volcanic rocks decompose very fast and are very rich agricultural soil
- The largest gold, copper, silver deposits are related to volcanoes
- Supply geothermal energy
- Recreation enjoyment
The Ring of Fire
- Most volcanoes found here in pacific
Magma
Molten rock inside of volcano
Lava
Molten rock outside of volcano
Pyroclastic material
Molten rock violently ejected from the volcano containing bombs, ash, and noxious gases
Bombs
Blobs of molten rock thrown into the air
Ash
Finely pulverized rock made up of fragments of the volcano walls, very light and can travel hundreds to thousands of km’s
Basaltic
Low viscosity magma containing 45-55% silica, cooling to a black to dark-grey rock called Basalt.
Andesitic
Intermediate viscosity magma containing 55-65% silica, cooling to a medium- to light-grey rock called Andesite.
Rhyolitic
High viscosity magma containing 65-75% silica, cooling to a white, pink, or light-coloured rock called Rhyolite
Rocks and Magmas: Silica
- The chemical compositions of many magmas are based on one mineral class, Silicates
- Made up up Silicon and Oxygen
Volatiles
- Gasses dissolved in magma
- Water most common volatile
- High volatile means low viscosity, and violent eruptions
Rocks and Magmas: Basalt
- 80% of the Earth’s igneous rocks are Basaltic;
- There are two textural types of Basaltic lavas:
- Aa(High viscous, rough)
- Pahoehoe (Low viscous, smooth)
Rocks and Magmas: Andesite & Rhyolite
- Chemically-altered Basalts
- The main ”modification” is the SiO2 content – though water content does play a large role in determining eruptive style and rock type
spreading centers
Magma that erupts at spreading centers is not melted; instead it’s described as a hot plastic that flows at just under its own melting temperature
Subduction Zones
- Here, the water-saturated oceanic crust plays a huge role in the production of magmas that feed often violent terrestrial volcanoes
- Most dangerous and violent volcanoes
Subduction Zones
Here, the water-saturated oceanic crust plays a huge role in the production of magmas that feed often violent terrestrial volcanoes
Pyroclastic Flow
- Avalanche-like rush of hot gas and pyroclastic material that can cover hundreds of meters in just seconds;
- Pompeii deaths
- Nuée ardente is a pyroclastic flow that glows red due to heat
Lahar
- Mudflows that contain pyroclastic material, water, trees, and anything else picked up on the way down the mountain
Volcanic Degassing
Noxious and greenhouse emissions released by a volcano
Lake Nyos, Cameroon (1986):
volcanic degassing occurred into Lake Nyos by underground volcanic vents, filling the summit lake with noxious gases; when a landslide triggered by an earthquake fell into the lake, it disturbed the gases that accumulated at the bottom, which spilled down the mountainside and onto the settlements below, choking the residents to death in their sleep; 1,700 people had died due to CO2 poisoning
Volcanoes States
Active, Repose, Dormant, and Extinct.
Short-Term Predictions
Precise and up-to-date, with danger zones identified; often use physical measurements of changes in the volcano to predict an eruption, based of its ”restlessness”
ST: Seismic Disturbances
- Common for volcanoes to be covered with seismic monitoring stations to diagnose the magmas within
- Short-period/High-frequency earthquakes indicate fracturing within the magma chamber;
- Long-period/Low-frequency EQs indicate the magma has left the chamber and is heading up to erupt
ST: Ground Deformation
As the magma builds up in the volcano reservoir, the ground will often bulge and deform; especially in the neck, where a magma dome can form
ST: Degassing Evolution
The composition of the gases expelled by a volcano can be used to predict whether an eruption is likely
Long-Term Predictions
General and observational, rooted in long-standing hazard assessment studies, rather than the current state of the volcano
Hazard Assessment
- Studying the current and historical behaviours of a volcano are integral in hazard assessment
- Historical record is not always reliable, so we look to the Geological evidence left by volcanoes
Other Indicators
Summit Lakes
Thermal Anomalies
Gravitational Tides
