Topic 5 Geohazard I - Volcanoes & Earthquakes Flashcards
(25 cards)
Where are volcanoes found?
All volcanoes are found where the mantle is melted into magma
What are the four types of Volcanoes?
Shield Volcanoes; Stratovolcanoes; Cinder Cones; Lava domes
Shield Volcano
a broad volcano form from innumerable layers of fluid basaltic lava laid down over yens to hundreds of thousands of years
Largest volcanoes on Earth
Slowly built
Stratavolcano
a large, potentially explosive, cone-shaped volcano composed of alternating layers of lava and pyroclasts
smaller, steeper sided, and composed of lava and volcanic ash
Lava Dome
Dome-shaped volcanoes that form when thick lava cannot easily flow piles around a volcanic vent and solidifiers into a domed structure
Far smaller than stratovolvanoes, typically only a few hundred meters high
May form on the flank of shield volcanoes and stratovolcanoes, or cap shield volcanoes and stratovolcanoes summit craters
Cinder Cone
Small, cone-shaped volcanoes consisting of pyroclasts
Generally smaller than 400m
symmetrical, settling at the angle of repose (steepest angle at which loose sediment can settle)
erupt for a few years or decades and them become extinct
Lava types
Mafic: Hottest, low viscosity, flows easily, Basaltic rocks
intermediate: Medium heat, medium viscosity, flows less easily, andesite rocks
felsic: lowest heat, High viscosity, does not flow easily, rhyolitic rocks
Volcanic Gases
~8% of most magma is gas
Consists of water vapor, carbon dioxide, sulfur dioxide, and hydrogen sulfide
Caldera
A large depression that forms when a volcano’s magma chamber empties and collapses after the volcano erupts
simplified: deflates into a crater
What are the two types of erruptions
Effusive eruption: nonexplosive erruption that produces mostly lava and lava flows. commonly at shield volcanoes associated with mafic lava
Explosive eruption: an eruption that sends rock, ash, and volcanic gases high into the troposphere (high in the air). commonly at stratovolcanoes associated with intermediate or felsic lava
Volcanic Explosivity Index (VEI)
ranks volcanic eruption magnitude based on the amount of material a volcano ejects during an eruption
ranges from 0 to 8 on a logarithmic scale (each whole number increase represents 10 times more material erupted).
Lahar
A thick slurry of mud, ash, and other debris that moves rapidly down the volcano’s flank
Generated by:
Snow melting due to volcanic eruption heat
dome collapse
heavy rain on erupted ash
catastrophic crater lake drainage
Pyroclastic flows
a quick-moving avalanche of gas and ash
speeds up to 700km/h
originate from collapse of eruption columns or landsliding of entire sectors of volcano
3 fault types
Normal fault: tensional force pulls two pieces of earth’s crust apart, called fault blocks
Reverse Fault: compressional forces pushes two blcoks together and upward in relation to another block
Strike-slip Fault: one block moves horizontally in relation to another block as a result of shearing (lateral) force
How do faults generate Earthquakes?
Earthquakes occur when stress exceeds friction.
crust breaks, and the blocks move.
Built-up stress energy is released and travels through the crust as seismic waves (earthquakes)
focus (Earthquake Terminology)
The location of initial movement along a fault during an earthquake
Epicenter (Earthquake Terminology)
the location on the ground’s surface immediately above the focus of an earthquake, where earthquake intensity is usually greatest
Foreshock (Earthquake Terminology)
A small earthquake that sometimes follows a larger Earthquake
Aftershock (Earthquake Terminology)
A small Earthquake that follows the main Earthquake
Seismic waves: Body Waves
Two types of body waves:
Primary waves: compression waves that travel through Earth’s interior
Secondary waves: shear waves that travel through Earth’s interior
Seismic waves: Surface waves
Two types of Surface Waves:
R waves: compression waves that travel through the crust’s surface, creating vertical, up-and-down crust movement
L waves: shear waves that travel through the crust’s surface, creating horizontal, side-to-side crust movement
What is a seismograph?
an instrument used to detect, measure, and record ground shaking
Modified Mercalli Intensity Scale
system used to rank the intensity of shaking during an earthquake
Categories:
I-III: slight
IV-VI: moderate to strong
VII-IX: very strong to violent
X-XII: intense to cataclysmic
Liquefaction
Transformation of solid sediments into an unstable slurry by ground shaking
