Earthquakes and Volcanoes Flashcards
Plates boundaries
3 types:
- transform
- convergent
- divergent
Divergent
plates move apart (divide), going in different directions, separate = two tectonic plates move away from each other.
–> Magma rises, cools, and forms new lithosphere = volcanic region
Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earth’s mantle to the surface, solidifying to create a new oceanic crust.
Crust is weakened: spread apart by convection cells moving things apart of each other
= thinner crust
—sea will fill the low lying seafloor
Rift Valleys and Mid Ocean Ridges
= mid-Atlantic ridge
= East African rift zone
First convective currents in the mantle start splitting apart the continent. As the rift valley expands, the continental crust thins and two separate continents are formed. And after some time the sea will fill the low lying sea floor.
On the side of the valley = layers of rocks + Land masses on either side of the water = two continents
The Deep Rift Valley runs along all of the planet’s ocean floor
→ deep rift valley = mid ocean ridge
→ The deep rift valley runs along all of the planet’s ocean floor
→ Mid ocean ridge = in the middle of the oceans
ex: Mid Atlantic ridge = line between the south american and the african continent, continuing to spread
East African Rift Valley
Iceland is bing split apart
Convergent
plates move toward each other = collide
= cause the edges of one or both plates to buckle up into mountain ranges or may bend down into a deep seafloor trench. A chain of volcanoes often forms parallel to convergent plate boundaries + powerful earthquakes
SUBDUCTION ZONES
ex: Japan, western coast of Americas, Caribbean, Mediterranean
The Himalayas: over millions of years; created by the collision of the Indian and Asian Plates.
Mt Everest (8850 m)
- Two continental plates could be colliding.
- Two oceanic plates could be colliding.
- A continental plate could be colliding with an oceanic plate
- or vice-versa
- Convergent continental plates move
towards each other, and when they meet
they can collide to form mountains - Oceanic to Continental Crust
= Japan
Oceanic Crusts moving towards other Oceanic Crusts
= Caribbean Island Arc
Transform
plates move past one another (slide), moving parallel to each other
fault zones and earthquakes = no volcanoes
ex: San Andreas fault
Pangea
Alfred Wegener = continental drift
- how to prove continental drift?
= fossils found on both sides of Atlantic
= structural evidence (mountain ranges)
= past climate and paleoclimatic evidence (Ice Sheets)
Faults
strike-slip = shearing / tearing
normal = tension
reverse thrust = compression
East African Rift Valley.
The Valley is growing 4 mm per year in one direction and 2 cm per year in another.
a place where the earth’s tectonic forces are presently trying to create new plates by splitting apart old ones.
Lake Victoria = goes nowhere because way below sea level –> will fill up and will not overflow because of evaporation // every lake flows into the ocean
Seismic waves
BODY waves = travel through the earth
P waves = primary waves
S waves = secondary waves
SURFACE waves = travel on earth’s surface
Subduction
The denser oceanic crust starts moving underneath the lighter continental crust
= subduction = “going under” zones or subduction zones.
The Andes Mountains = mountains being
created by subduction.
Eruption of Mount St Helen
- Before the eruption an
earthquake triggered a massive
landslide
Caribbean Island Arc
has been around for millions of years = active zone moved along with the plates over time
St Vicent: stratovolcano la souffriere
shield volcanoes
Mount Kea (Hawai)
Mount Etna (Sicily)
basalt, a type of lava that is very fluid when erupted
low viscosity
built by repeated eruptions that occurred intermittently over vast periods of time
gentle slopes
-CALDERA
at summit = may contain long-lasting lava lakes + pit craters = smaller collapse structures.
lakes: good connectivity between the vent and the magma supply
-oceanic hot spot
-mid-ocean spreading ridges
-Eruptions that occur along rift (fissure) zones are a major feature of some shield volcanoes, particularly the shield volcanoes that make up Hawaii
=== because area of weakness
Stratovolcano
// composite volcano
rock type: andesite
intermediate viscosity
built up of alternating layers of lava flows and pyroclastic deposits (ash and lava layers)
Parasitic cone
vent crater
= ‘a’a lava
= pile up in the vent to form volcanic domes. = collection of domes piled up on each other.
explosive
subduction zones
landslides, avalanches, and mudflows
lahars = mudflow on an active volcano
Mount Fuji
Mount St Helens
Volcano domes and cinder cones
dome = high viscosity + Rhyolite rock type
—collapsed
cinder = summit crater + low viscosity + Basalt rock type
General info on volcanoes
- Ring of Fire
- eruption depends on:
–> viscosity = lava’s resistance to flow, composition and temperature of lava
–> amount of gas dissolved
high viscosity = explosive
Turkey earthquake
7.8 magnitude
cause earthquake
tectonic movement causes stress on litosphere
= fractures –> faults
stress produces strain (deformation)
1) original position
2) buildup strain
3) slippage = earthquake
4) strain released
focus = point below the earth’s surface where the fault rupture starts
epicenter = point of earth’s surface directly above the focus = ground level
elastic rebound
the rock elastically returns to original shape
