Tectonic gateway 2 part 1 argh

Question 1

Landforms at plate boundaries

3

Answer 1

1. fold mountains
2. rift valleys and block mountains
3. volcanoes

Question 2

fold mountains elab

Answer 2

• upfold: syncline
• downfold: anticline
• when there is more compressional force on one limb, the rocks buckle, a fracture is formed and the limb moves forward onto the other limb
• eg Himalayas mountain range

Question 3

how are volcanoes formed?

Answer 3

• magma ejected from the mantle onto the earth’s surface as lava builds around the vent to form volcanoes
• At subduction zones, mantle material melts, forming magma. As magma is less dense than surrounding rock, it rises and accumulates in the magma chamber. The pressure builds up and the magma forces its way to the earth’s surface through vents

Question 4

where are volcanoes found?

Answer 4

• where there is subduction
• found at divergent and convergent plate boundaries
• shield volcano found at divergent plate boundaries where magma rises directly from the mantle

Question 5

structure of a stratovolcano and how it forms eruptions of ash

Answer 5

1. magma seeps into the magma chamber and pressure builds up
2. When it erupts pyroclasts are released. The force of the eruption depends on the amount of pressure built up in the volcano
3. A new eruption of lava covers the pyroclasts
4. Lava builds up around the vent, forming small volcanic cones. The bowl-shaped opening is the crater
5. if the vent is blocked, the magma finds a new exit route and a secondary cone develops
6. The summit may be blown off in an explosive eruption and the sides collapse inwards

Question 6

types of lava

Answer 6

Low silica lava
-low viscosity, less explosive eruptions
-gases escape easily , lava flows more easily, outer layer forms a thin crust
High silica lava
-high viscosity, more explosive eruptions
-gases trapped easily, gases expand, outward explosion that ejects lava, ash, rock fragments, gases

Question 7

Shield volcano vs Stratovolcano

1. shape
2. type of lava
3. What it is made of
4. is the eruption explosive?
5. are there secondary cones?

What did one volcano say to the other?
I lava you

Answer 7

Shield vs strato

1. gently sloping sides, broad summit vs steeper top, gentler base with a concave profile
2. low silica lava vs high silica lava
3. lava accumulates and base increases after successive eruptions vs formed from successive eruptions of lava and pyroclasts (after initial eruption of pyroclasts, subsequent eruption ejects lava which cover the pyroclasts and prevents it from being eroded away)
4. no vs yes
5. no vs yes when the vent is blocked

Question 8

pyroclasts elab (mixes with _____ to form _____)

Answer 8

• mixes with super-heated gases to form pyroclastic flow which reaches speeds of up to 200m/s
• mixes with water to form lahars

Question 9

distribution of volcanoes

Answer 9

• majority found at pacific ring of fire at convergent plate boundaries around the pacific ocean
• found at divergent plate boundaries

Question 10

Phenomena found at plate boundaries

2

Answer 10

1. Earthquakes

2. Volcanic eruptions

Question 11

How are earthquakes and aftershocks formed?

Answer 11

• Stress builds up between plates. When the plates are unable to withstand the stress, there is a sudden and quick release of stored energy and plates slip many metres. The energy from the plates radiates outwards in all directions in the form of seismic waves
• The stress can cause many smaller earthquakes known as aftershocks which can occur several months after the original earthquake and can be as powerful as the initial earthquake. It occurs along the fault lines

Question 12

How to measure the magnitude of earthquakes?

Answer 12

• The Ritcher scale is used to measure the magnitude of an earthquake. The deeper the focus, the lower the magnitude
• higher magnitude earthquakes usually cause more damage and destruction

Question 13

types of earthquakes

Answer 13

deep focus earthquakes vs shallow focus earthquakes

Deep focus earthquakes

• 70-700km deep
• smaller impact as vibrations and seismic waves take a longer time to reach the surface so it will lose most of its energy

Shallow

• less than 70km deep
• greater impact as vibrations and seismic waves reach the surface more quickly

Question 14

What determines the extent of earthquakes?

5

Answer 14

1. population density
2. time of occurrence
3. level of preparedness
4. distance from epicentre
5. type of soil

Question 15

population density elab

Answer 15

• in places that are sparsely popluated, less people are affected
• in a city which is very densely populated, there will be more damage and casualties

Question 16

time of occurrence elab

Answer 16

• determines where people are, what they are doing and this affects their chances of survival
• if the earthquake occurs at night and people are sleeping, there is a higher chance of people being trapped, leading to more deaths

Question 17

level of preparedness elab

Answer 17

the damage is more manageable when people are better prepared

Question 18

distance from epicentre elab

Answer 18

• when the distance from the epicentre is higher, the damage is less severe
• eg Christchurch earthquake, 2011. The epicentre was only a few kilometres away so it suffered more damage than cities further away

Question 19

type of soil elab

Answer 19

• when sediments are loose and unconsolidated, the seismic waves are amplified and it does greater damage
• structures on saturated and unconsolidated sediments are affected by liquefaction which is when the ground is unstable and acts as a liquid

Question 20

location of earthquakes

Answer 20

• mostly at convergent plate boundaries because there is more stress when a plate subducts
• majority at pacific ring of fire

Question 21

how to measure earthquakes?

Answer 21

• a seismograph record seismic waves released by an earthquake. The weight moves up and down when tremors are detected and the ink marker across the motions, and make vertical markings
• The distance that a location shifts is related to the magnitude of an earthquake. By measuring the distance that a location shifts, we can calculate magnitude. A GPS is used to measure how far a location has shifted as a result of the earthquake.