E1 Dynamic Earth

Question 1

How extrusive and intrusive rock formed respectively?

Answer 1

Extrusive - during extrusive volcanism, lava or other volcanic materials will be ejected. When they are in contact with air, they cool and solidifies on earth’s surface rapidly. Crystallisation takes pace and forms minerals. They aggregate to form rocks.

Intrusive - during intrusive volcanism, magma cools and solidifies deep within the crust. Crystallisation takes place in magma to form minerals. The aggregate of minerals forms rocks.

Question 2

Describe the similarities and differences of intrusive/plutonic rock and extrusive/volcanic rock (igneous rock)

Answer 2

Extrusive - fine grained due to fast cooling rate of lava, may hv flow bands (rhyolite)
Intrusive - coarse grained due to slow cooling rate of magma
Similarities - crystalline, usually non-stratified, hard and compact, well-jointed, the higher the silica content, the lighter the colour, no presence of fossil

Question 3

Characteristics of granite (a type of intrusive / plutonic rock)

Answer 3

-crystalline structure with interlocking minerals
-coarse-grained due to slow cooling rate of magma
-hard and compact
-well-jointed
-light colour as silica content is high
-type of acidic rock

Question 4

Give two examples of extrusive rock

Answer 4

Tuff
Rhyolite

Question 5

Give two examples of intrusive/plutonic rock

Answer 5

Granite
Gabbro

Question 6

How are clastic sedimentary rocks formed? (Hint: 6 steps)

Answer 6

1. Loose fragments and grains are produced by weathering and erosion
2. Weathered materials moved downhills (transportation)
3. Sediments is deposited in shallow water (sedimentation&deposition)
4. Sediments accumulates and compacted by weight of overlying layers (compaction)
5. Minerals dissolved in water cement the loose materials together (cementation)
6. Loose materials is transformed into solid rock (lithification)

Question 7

Characteristics of clastic sedimentary rocks

Answer 7

-stratified with bedding planes and strata since deposition and sedimentation take place
-fine-grained since sediments are well sorted
-less compact and soft
-non-crystalline
-may contain fossils since remains of plants or marine species embedded into the sediments

Question 8

Name six clastic sedimentary rocks

Answer 8

Conglomerate and breccia (coarse-grained)
Sandstone (medium-grained)
Mudstone, shale and siltstone (fine-grained)

Question 9

Characteristics of non-clastic sedimentary rock

Answer 9

-materials formed chemically or organically
-less compact than igneous rock
-may hv fossils

Question 10

Name four non-clastic sedimentary rocks

Answer 10

Gypsum and rock salt (chemically-formed)
Limestone and coal (organically-formed)

Question 11

Name the three metamorphism

Answer 11

Dynamic metamorphism (high pressure)
Thermal metamorphism (high temperature) e.g. limestone—>marble
Regional metamorphism (high temp+pressure) e.g. granite—> gneiss

Question 12

What are foliated metamorphic rock and non-foliated metamorphic rock?

Answer 12

Foliated metamorphic rock- metamorphic rock formed under high pressure have a foliated structure
Non FMR - MR formed under high temperature have a crystalline structure

Question 13

Examples of metamorphic rock

Answer 13

Granite—>gneiss
Sandstone—>quartzite
Shale—> slate
Limestone—> marble

Question 14

Name the four common rocks in Hk

Answer 14

Granite (intrusive/plutonic rock)
Tuff (extrusive rock)
Conglomerate (clastic sedimentary rock)
Siltstone (clastic sedimentary rock)

Question 15

Name the internal processes that shape the natural landscape of Hk

Answer 15

Extrusive and intrusive volcanism
Folding
Faulting

Question 16

Process of block disintegration (physical weathering)

Answer 16

1. During that day, rock heated and expands as they absorb solar energy.
2. At night, rocks cool and contract, stress is created and cracks are produced.
3. Repeated expansion and contraction of rock enlarge the joints or cracks on the rock.
4. Rocks break into blocks.
   ⭐️commonly found in areas with large diurnal range of temp
   ⭐️common on rocks which are well-jointed with many cracks e.g. granite

Question 17

Process of granular distintegration (physical weathering)

Answer 17

1. During the day, rocks expand as they absorb solar energy
2. At night, rocks cool and contract
3. As different minerals expand and contract at different rate, rocks with variety of minerals are under stress during repeated heating and cooling
4. Rocks break into individual grains
   ⭐️coarse-grained rocks tend to have faster granular disintegration

Question 18

Process of exfoliation (physical weathering)

Answer 18

1. During the day, rocks heated and expand as they absorb solar energy
2. At night, rocks cool and contract
3. The outer layer looses heat faster and contract more than the inner layer
4. This crates stress on the outer layer and radial cracks develop
5. Layers or sheets of rocks peel off the main rock under repeated heating and cooling
   ⭐️usually occur in fine-grained rocks

Question 19

Process of Honeycomb weathering (crystal growth)

Answer 19

1. Saline solution seeps into pores in coastal rocks
2. Evaporation and crystallisation take place, salt crystals left in the pores
3. They accumulate and grow in the pores
4. Minerals break off and forming many small pits on rock surface

Question 20

Name the four type of chemical weathering

Answer 20

Solution and carbonation
Oxidation
Hydrolysis
Hydration

Question 21

Process of spheroidal weathering (chemical weathering)

Answer 21

1. Water seeps through joints
2. Spheroidal weathering works from the joints towards the intersection of rock
3. Large amount of loose and fine materials are produced
4. Erosion remove the loose and fine materials
5. Unweathered corestone pile up forms tors

Question 22

Why a thick/deep weathering profile is formed in Hk?

Answer 22

Heavy and high rainfall and high temp causes active chemical weathering
Large area of granite which is well jointed and less resistant to weathering

Question 23

Characteristics of weathering profiles in Hong Kong

Answer 23

Deep and thick
Top layer is fine regolith (soil) where granite is completely weathered
Unweathered corestone distributed in regular way
Smallest one is near the top layer;larger one is close to the bedrock
Corestone that are close to the top layer is rounded and those closer to the bedrock is angular

Question 24

Formation of rills, gullies and badlands

Answer 24

1. Vegetation is removed and the topsoil is exposed
2. Cracks are developed since topsoil contract
3. In rainy season, water flows through the cracks, making it widened and deepened
4. A narrow channel called rill is formed
5. Water continue to flow and widen the rill into gully
6. Dense concentration of gully formed badland

Question 25

Favourable condition of forming rill, gully and badland

Answer 25

-soil is acidic and poor —> difficult for vegetation to grow -frequent hill fire and wood cutting —> no vegetation -in summer, heavy rain increase the surface runoff —> topsoil easily removed -in winter, strong wind blow away the topsoil and difficult for vegetation to grow -deep weathering profile produced by weathered granite -steep hill slopes -active chemical weathering

Question 26

Why physical weathering is common in Hk?

Answer 26

Granite is the major type of rock in Hk Well-jointed Vulnerable to weathering / less resistant to weathering Large diurnal range of temp in hot summer days