HKDSE Geography/E1/Hills

Granite Hills 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 → Denudation (weathering and erosion) ↑ → Low and rounded, thick colluvium layer Formation: Magma in the asthenosphere is under great pressure. A line of weakness develops in the crust and reaches the magma chamber below. The magma rises through the line of weakness and into the earth's crust. It cools and solidifies at a very slow rate in a dome-shaped magma reservoir. Crystallisation occurs. It becomes a plutonic rock called a granite batholith. As Hong Kong's climate is hot and wet, active chemical weathering and erosion remove the layer above. 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 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 / 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: