HKDSE Geography/E1/Hills

Granite Hills
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
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
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: