Lecture 3 - Earthquakes and Volcanoes

Question 1

What is the most common reason for an earthquake?

Answer 1

Movement of the plates

Question 2

Epicentre?

Answer 2

The point where the seismic rupture begins (origin)

Question 3

Seismograph?

Answer 3

Used to measure an earthquake

Question 4

Earthquake magnitude?

Answer 4

Measured by moment magnitude, logarithmic, quantitative measurement (M1, M5, etc.)

Question 5

Earthquake intensity?

Answer 5

Modified Mercalli intensity scale: qualitative, based on damage to structures/perceptions (I - XII)

Question 6

Shake maps?

Answer 6

Use seismograph data to show areas of intesnes shaking

Question 7

Dip slip fault?

Answer 7

Vertical movement, includes Normal, Reverse, and Blind

Question 8

Hanging wall?

Answer 8

The top wall of a fault

Question 9

Footwall block?

Answer 9

The bottom wall of a fault

Question 10

Normal fault?

Answer 10

The hanging wall moves down

Question 11

Reverse fault?

Answer 11

The hanging wall moves up

thrust fault: if a reverse fault is 45º or less

Question 12

Blind fault?

Answer 12

Don’t extend to the surface

Question 13

Strike slip fault?

Answer 13

Horizontal movement: the plates slide past eachother

Question 14

Active fault:

Answer 14

movement during the past 11 600 years

Question 15

Potntially active fault:

Answer 15

movement during the past 2.6 million years

Question 16

Inactive fault:

Answer 16

no movement in the last 2.6 million years

Question 17

Tectonic creep?

Answer 17

Movement along a fault is so gradual that earthquakes are not felt

Question 18

P waves (primary/compressional)?

Answer 18

move fast with a push/pull slinky motion, good in all states of matter

Question 19

S waves (secondary/shear?)

Answer 19

moves like a water wave, but only through solids

Question 20

Surface waves?

Answer 20

rolling waves on the surface that move more slowly than body waves

Question 21

Love waves

Answer 21

surface waves that cause horizontal shaking

Question 22

Rayleigh waves

Answer 22

surface waves with rolling motion

Question 23

How can distance to the epicentre be determine from S and P waves?

Answer 23

Compare travel times of the two wave types using triangulation

Question 24

When does amplification occur?

Answer 24

When energy is transferred from P and S waves to surface waves

Question 25

What are the steps of the earthquake cycle?

Answer 25

- inactive period (stress builds) - foreshock (occur prior to major release) - main shock (majority of the stress is released) - aftershock (releases of stress after major earthquake)

Question 26

Intraplate Earthquakes?

Answer 26

Occur within plates, not at a boundary | - often smaller than plate boundary earthquakes

Question 27

Precursor?

Answer 27

An event that signals that an earthquake may be imminent - pattern/freq of earthquakes - land level change (uplift/subsidence) - seismic gaps (haven't seen an earthquake in a while) - physical/chemical changes

Question 28

How much time does the current warning system give for an earthquake?

Answer 28

15s to one minute

Question 29

Where are 2/3 of all active land volcanoes found?

Answer 29

Pacific Ring of Fire

Question 30

Magma

Answer 30

molten rock

Question 31

Lava?

Answer 31

magma that reaches the earth's surface

Question 32

Pyroclastic debris?

Answer 32

Leava and rock fragments ejected in a volcanic eruption

Question 33

Volcano?

Answer 33

hill or mountain produced by volcanism

Question 34

Vent?

Answer 34

opening through which eruption akes place

Question 35

Crater?

Answer 35

depression over the vent

Question 36

Caldera?

Answer 36

a depression over 1km wide

Question 37

Where does most magma come from?

Answer 37

Asthenosphere

Question 38

Decompression

Answer 38

Magma is formed - pressure on hot rock is reduced

Question 39

Addition of volatiles

Answer 39

Magma is formed - chemcial compounds lower the melting temp of the rock

Question 40

Addition of heat

Answer 40

Magma is formed - heat overlying rocks as magmas rise

Question 41

What are the two most abundant elements in magma

Answer 41

Silica and Oxygen - SiO2

Question 42

Silica-Rich (felsic) Lavas

Answer 42

Very viscous, flow slowly - violent explosive eruptions - rhyolite

Question 43

Silica-Poor (mafic) lavas

Answer 43

Low viscosity, flow easily, quiet eruptions/lava flows | - basalt

Question 44

Intermediate lavas

Answer 44

Andesite

Question 45

Shield Volcanoes

Answer 45

- largest volcanos in the world - arch/dome - low silica (mafic) lava - basalt - not too explosive - mauna loa (hawaii)

Question 46

Composite Volcanoes

Answer 46

- Cone shaped - intermediate lava, high silica but low viscosity - andesite (dicitic) - lava flows and explosive activity - volcan osorno, chile

Question 47

Volcanic Domes

Answer 47

- dome shaped - high silica (felsic) magma - very explosive - rhyolite - mono craters, california

Question 48

Cinder Cone Volcanoes

Answer 48

- steep cone - low silica (mafic) magma - not very explosive - basalt - mount edziza, BC

Question 49

Maars?

Answer 49

The interaction of magma and groundwater: produces roughly circular craters filled with water

Question 50

Ice Contact Volcanoes

Answer 50

Erupt beneath or against glaciers

Question 51

Jokulhaups

Answer 51

Huge floods produced from subglacial volcanoes

Question 52

Hot springs

Answer 52

hot rocks heat grounwater that discharges at the surface

Question 53

Geysers

Answer 53

Groundwater boils an underground chamber, erupting steam at the surface

Question 54

Resurgent Calderas and super eruptions

Answer 54

very rare but very violent eruptions from supervolcanoes

Question 55

Highest mountain in canada?

Answer 55

mt logan

Question 56

Volcano that poses the biggest threat to Canada?

Answer 56

Mt baker in washington

Question 57

What are some primary effects of a volcano?

Answer 57

Lava flows, ash fall, volcanic bombs, pyroclastic flows, pyroclastic surges, lateral blasts, poisonous gases

Question 58

Secondary effects of a volcanic eruption?

Answer 58

Lahars (mudflow), debris avalanches, landslides, groundwater/surface contamination, floods, fires, tsunamis

Question 59

Two types of balsaltic lava flows?

Answer 59

Pahoehoe (smooth ropy texture, faster) | Aa (more viscious, more damaging, slow)

Question 60

Sector Collapse

Answer 60

the flank of a volcano may collapse due to shaking

Question 61

Mt St Helens

Answer 61

``` May 1, 1980, a large bulge began to grow May 18, a M5.1 earthquake triggers a landslide/debris avalanche Seconds later, a LATERAL BLAST Cloud of ash Mudflows (Lahars) 57 People Killed ```

Question 62

How can we manage volcanoes?

Answer 62

- Bombing (block channels to cause lava flows to take a dif route) - Hydraulic Chilling (water) - Wall construction