HKDSE Geography/E1/Hills

Granite Hills

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

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

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: