Schol ZEALANDIA

Question 1

the two plates of Zealandia

Answer 1

Indo-Australian and Pacific plates

more buoyant continental, denser oceanic

Question 2

types of boundaries in Zealandia

Answer 2

convergent (subduction)

transform (lateral movement)

Question 3

describe the differences between troughs and trenches

Answer 3

both occur at SUBDUCTION zones…
troughs = oceanic and continental
big difference in density, hence SHALLOW angle (drags overriding plate slightly).
shallow depression.
trenches = oceanic and oceanic
similar density, hence STEEPER angle of subduction, deforms the overriding plate more.
deeper depression

Question 4

describe the features of the Kermadec subduction zone, and the hazards

Answer 4

upper North Island
fastest converging, most seismically active plate boundary on earth (58mm/year)
has the highest density of submarine volcanoes
Islands (Raoul, Macauley) are peaks of volcanoes

tsunami hazards due to earthquake activity.
submarine cone collapse –> pyroclastic flows impacting water

oceanic/oceanic –> Kermadec Trench (8km deep)
older pacific plate subjects under younger Aus Plate

Question 5

describe the features of the Hikurangi subduction zone and the hazards associated with it

Answer 5

on the East of the NI
denser oceanic PP subducts continental AP

potentially the largest earthquake / tsunami hazard for NZ (as there would only be a 3 minute tsunami warning)

World’s shallowest ‘slow slip’ events occur off the coast of Gisborne

The Taupo volcano zone on the AP is parallel to the HSZ

Question 6

describe the features and hazards of the Puysegur subduction zone

Answer 6

below the SI
oceanic/oceanic, AP subducts PP, trench 6km deep

Alpine fault starts at the Northern end of the trench.
Macquarie Ridge lies to the east. (different system)

highly seismically active, with magnitude 7.2 and 7.8 earthquakes occurring in the last 20 years.

Question 7

describe the processes and features of the Southern Alps

Answer 7

continental AP (moving NE) and PP (moving SW), transform
PP overrides, uplifting land to form the Alps
forms transform fault (Alpine)

metamorphic rocks of deep origin are uplifted.

Question 8

two types of volcanism in Zealandia and where they occur

Answer 8

subduction zone (Kermadec, Hikurangi) 
hotspot (Auckland field)

Question 9

describe the general process of a volcanic eruption for a subduction zone

Answer 9

PP subducts AP
at a certain depth, rock melts
magma rises through cracks/vents, erupts.

Question 10

Describe the Taupo Volcanic zone system

Answer 10

formed along the Hikurangi
leading edge of the subduction zone bends down, stretches the overriding plate, which thins.
large magma chamber closer to the surface
hence geothermal activity near Taupo.

material brought to the surface is from both PP and AP, transfer of continental crust from PP to AP.

andesite (Ruapehu, Ngaruhoe) and rhyolite (Rotorua, Taupo) volcanoes.

Question 11

Describe the Kermadec Volcanoes

Answer 11

mostly submarine basalt and andesite cones (forming the kermadec Ridge)

increasing number of rhyolitic caldera volcanoes discovered

Question 12

describe the process of a hotspot volcano

Answer 12

caused by a plume of basalt magma below crust, in an area typically far from a plate boundary.
low viscosity ‘lava fountain’ eruption

forms chains of volcanoes - hotspot remains in the same place but the plate moves, linear pattern.
shows late movement direction (so a chain of volcanoes suggests tectonic activity)

Question 13

describe the Auckland Volcanic Field

• -> how volcanoes are created
• -> plate tectonics interaction
• -> types of volcanoes

Answer 13

A plume about 100km from the surface.
each volcano is a different path the magma took to the surface - all from the same chamber

subduction of the east stretches overriding AP, causing cracks under Auckland, allowing magma to reach surface.

mostly scoria cones (basalt + water)

Question 14

what are slow slip events?

Answer 14

the release of pressure (tectonic stress) at a SUBDUCTION BOUNDARY over a long time
(causes movement associated w/ a mag 6+ eq over months)

usually cannot be detected on seismographs, identity land movement with GPS

Question 15

the pros and cons of slow slip events

Answer 15

can both relieve and transfer stress.

relieve: reduces risk / delays a major earthquake
potential use - predict eq

can load tress onto another part of the boundary, causing fault ruptures –> large eq
eg. Kapiti slow slip led to 2014 Eketahuna eq by loading stress onto nearby fault, causing it to break.

Question 16

describe the Hikurangi system in terms of the slow-slip plate boundary

Answer 16

between AP and subducting PP, there is the steady creeping zone (normal mvmt), the slow slip zone and the stuck plate interference.
this is lower in the SI.
stuck = adhesion between rocks
huge tectonic stresses built up over time may be released in a decoupling event, producing a mega thrust EQ (mag 8+)

slow slip events further north (Gisborne/Hawkes Bay) may increase pressure on ‘stuck’ section.

Question 17

what is a turbidity current?

Answer 17

a rapid, downhill flow of denser sediment-laden water (underwater landslide)
sediment travels downslope (towards the abyssal plane), picking up more sediment as it goes, so it deposits a large amount.

Question 18

what causes a turbidity current?

Answer 18

sediment builds up on continental shelf (the shallow area off the coast of a landmass), loosened by a geological event (earthquake)

Question 19

what information do turbidites reveal?

Answer 19

Each turbidite layer is indicative of a geological event.
easy to identify, as larger particles settle first (density flow), forming classic turbidite layers.
hence distinct boundary between each turbidite unit.

contain BOTH SHALLOW AND DEEP WATER ORGANISMS.

may be a layer of pelagic (normal Si/Ca type sediments) between turbidites, but it takes a long time to settle, typically a thin part of the core sample.

Question 20

At what location are turbidity currents common?

Answer 20

Kaikoura Canyon

Question 21

describe the features of the Kaikoura Canyon

Answer 21

60km long, 2km deep submarine canyon, 500m off the coast of Kaikoura.
very shallow continental shelf –> deep abyssal plane.

joins the Hikurangi Channel, which meanders on the Hikurangi plateau

Question 22

Why are turbidity currents common in the Kaikoura canyon?

Answer 22

the canyon is the sink for the coastal transport system

carries eroded material deposited by rivers draining from the Southern Alps.

Question 23

how are turbidity currents created in the kaikoura canyon?

Answer 23

every few hundred years, EQ loosens the materials built up at the head of the canyon.

flows down the Hikurangi channel at 30km/h, depositing layer in the Hik Trough

Question 24

what do sediment cores from the Hikurangi trough show?

Answer 24

regular deposition events.

eg. 2016 kaikoura EQ, 10cm of new, loose deposit.