dynamics of earth's crust

Question 1

internal structure of the earth

Answer 1

1. crust
2. mantle
3. outer core
4. inner core

Question 2

core

Answer 2

2 distinct regions

Liquid outer core (2,300 km thick)

Solid inner core (1,200 km thick)

Makes up significant proportion of Earths mass due to very high density

Comprised mostly of iron and some nickel

Question 3

mantle

Answer 3

Thick layer of rock that separates the core from the crust (2,800 km thick)

Makes up most of the earths volume

Much richer in iron and magnesium than the crust which makes it more dense

Question 4

crust

Answer 4

Outer layer of rock that forms a thin skin over the earths surface (up to 70 km thick under mountain ranges)

Less dense than the mantle (least dense layer)

2% of earths volume and less than 1% of earths mass

Question 5

what kinds of crust exist

Answer 5

continental and oceanic crust

Question 6

what is continental crust

Answer 6

(sial composition)-the material of the upper or continental part of the earth’s crust, characterized as being of relatively low density and rich in silica and alumina.
25-70 km thick
Rich in silicates and aluminum (granitic)
Lighter and less dense than oceanic crust so it floats higher

Question 7

what is oceanic crust?

Answer 7

composed of sima (the material of the lower part of the earth’s crust, underlying both the ocean and the continents, characterized as relatively dense and rich in silica and magnesia.)
5-7 km thick

Rich in silicates and magnesium (and iron) which make it very
dense (basaltic)

Thinner, denser & younger than continental crust

Question 8

what makes up tectonic plates?

Answer 8

lithosphere

Question 9

what is the lithosphere?

Answer 9

crust + upper mantle (~100 km)

Question 10

what’s is plate tectonics?

Answer 10

massive, irregularly shaped slab of solid

rock, often composed of both continental and oceanic crust

Question 11

what is continental drift?

Answer 11

theory proposed in 1915 by Alfred Wenger which says that
continents migrate around the planet
like ice floes

Question 12

evidence for plate tectonics

Answer 12

In the 40s and 50s, development of echo sounders led to the discovery of mid-ocean ridges (underwater mountain chains)

1978: glomar challenger deep sea drilling rig that cross-crossed the mid Atlantic ridge between South America and Africa

Question 13

evidence from deep sea cores

Answer 13

Crust youngest at the ridges, where plates are moving away from each other

Question 14

evidence from temperature data

Answer 14

Water hottest at the plate boundary using bathythermographs

Question 15

evidence using magnetometers

Answer 15

Records magnetic field of the earth

Magnetic orientation reversals periodically occur

Question 16

what’s challenger expedition?

Answer 16

Concluded that there is growth of ocean
floor at mid-ocean ridges where new (thin)
crust is formed over convective currents in
the asthenosphere

Question 17

what is asthenosphere?

Answer 17

The asthenosphere is a part of the upper mantle just below the lithosphere that is involved in plate tectonic movement and isostatic adjustments. It is composed of peridotite, a rock containing mostly the minerals olivine and pyroxene.

Question 18

how’s asthenosphere ‘plastic’?

Answer 18

Asthenosphere is solid but it flows through the deformation of the rock
a part of the upper mantle just below the lithosphere that is involved in plate tectonic movement and isostatic adjustments
- also due convection which shapes the earth

Question 19

what are the seven major tectonic plates

Answer 19

African, North American, South American, Eurasian, Australian, Antarctic, Pacific

Question 20

minor plates and movement

Answer 20

Several minor plates like the Juan de Fuca, Arabian, Nazca, and Philippines plates

Plates are all moving different directions and at different speeds

Movement likely due to convection cells in mantle which carry plates along

Question 21

Evidence from seismic data &

volcanism

Answer 21

Nearly all of the world’s earthquakes and active volcanoes occur along or near the boundaries of the Earth’s shifting plates

Question 22

where are the hawaiian volcanoes

Answer 22

3000 km from any plates

Question 23

hotspot data

Answer 23

Used to measure rate and direction of movements of the Pacific plate

Heat from the Hawaiian hot spot is where the mantle plume comes up and spreads out

Question 24

what are the 3 types of plate tectonics?

Answer 24

divergent
convergent
transform

Question 25

divergent

Answer 25

New crust is generated as the plates pull away from each other (youngest crust at ridges)
plates moving away from each other, new material comes in between through convection solidifies when it comes in contact with water- so it is growing

Question 26

convergent

Answer 26

(destructive margins/subduction zones):

Crust is destroyed as one plate is subducted under another

two plates coming together, crust destroyed, the more dense one goes underneath, destructing the margin, rock melted back into the mantle and removed from the plate, earthquakes come from convergent boundaries

Question 27

transform

Answer 27

rust is neither produced nor destroyed but the plates slide horizontally past each other

Question 28

what’s the difference between ridge and rise

Answer 28

Rise are faster spreading, they are not as tall and are flatter

Ridges are slower spreading, taller, forms rift valley

Question 29

how do continents move?

Answer 29

Continents have been coming together and separating for hundreds of millions of years

Pangaea: supercontinent formed approximately 345 mya

About 190 mya, Pangaea broke up into 2 large continents

Laurasia (N. America and Eurasia) and Gondwanaland (Africa, Arabia, Australia, Antarctica, India, South America)

Question 30

fracture zone

Answer 30

Extend past the transform faults, away from the ridge axis

Fracture zones are usually not at plate boundaries but transect mid-ocean ridges

Question 31

explain the transform fault/boundary in blanco fracture zone

Answer 31

transform boundary- is a fault along a plate boundary where the motion is predominantly horizontal.

Although earthquakes occur frequently along the Blanco Fracture Zone, they are rarely felt

Generally, the transform motion does not produce tsunamis because the horizontal motion of the does not raise or lower the seafloor as is
required to produce a tsunami

Question 32

what conditions the tsunamis

Answer 32

large waves generated by

• Subsidence
• Submarine landslides
• Meteorites large enough to displace a large volume of water
• Volcanic eruptions (Tonga 2022)
• Calving glaciers

Question 33

how does a tsunami look

Answer 33

Wave characteristics change as it crosses the ocean and approaches shore

In the open ocean a wave may be less than one meter
high with a period of 10 to 30 minutes and a
wavelength of 100 – 200 km (1000 km/h)

At the shore, however, the wave may be 100 m high
with a shorter wavelength as the energy of the wave is compressed into a smaller column of water

Question 34

what’s convection

Answer 34

the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat