HKDSE Geography/E1/Hills

From Wikibooks, open books for an open world
Jump to navigation Jump to search

Granite Hills[edit]

Internal Processes External Processes Rock Types Human Activities
Intrusive Vulcanicty - Batholith Intrusion Denudation:
  • Chemical weathering
  • Erosion
  • Mass Movement
  • Physical weathering by pressure release
Granite /

Characteristics:

  • Low
  • Rounded
  • Thick weathering profile

Underlying reasons: Non-resistant and well-jointed → Chemical weathering ↑ → Erosion ↑ → Mass Movement ↑ → Low and rounded, thick colluvium layer

Formation:

  1. Magma in the asthenosphere is under great pressure.
  2. A line of weakness develops in the crust and reaches the magma chamber below.
  3. The magma rises through the line of weakness and into the earth's crust.
  4. It cools and solidifies at a very slow rate in a dome-shaped magma reservoir. Crystallisation occurs.
  5. It becomes a plutonic rock called a granite batholith.
  6. As Hong Kong's climate is hot and wet, active chemical weathering and erosion remove the layer above.
  7. The batholith is exposed to the surface to produce granitic hills.

Examples:

  • Both sides of Victoria Harbour
  • Castle Peak and Tai Lam Chung
  • Shatin
  • Northern part and southernmost tips of Hong Kong Island, the northeastern part of Lantau Island, most of Lamma Island, Po Toi Island, and the Soko Islands

Tuff Hills[edit]

Internal Processes External Processes Rock Types Human Activities
Extrusive Vulcanicty Denudation:
  • Chemical weathering
  • Erosion
  • Mass Movement

(Very little occurs)

Tuff /

Characteristics:

  • Rugged and uneven
  • High

Underlying reasons:

  • High resistance, few joints → Less chemical weathering → Less erosion → Less mass movement → Higher, rugged

Examples:

  • N/E/Central NT (e.g. Tai Mo Shan, Sai Kung)
  • Western Lantau (e.g. Lantau Peak), southern Hong Kong Island

Sedimentary Rock Hills[edit]

Internal Processes External Processes Rock Types Human Activities
/ Differential Erosion Mechanically-formed sedimentary rocks:
  • Conglomerate, breccia (resistant)
  • Sandstone, siltstone, mudstone, shale (non-resistant)
/

Characteristics:

  • Uneven
  • Varying Height
  • Ridges

Underlying reasons:

  • Non-resistant and well-jointed (e.g. shale) → Chemical weathering ↑ → Erosion ↑ → Mass Movement ↑ → Low and rounded, thick colluvium layer
  • High resistance, few joints (e.g. conglomerate) → Less chemical weathering → Less erosion → Less mass movement → Higher, rugged

Examples: