Polar

Description

·         Weak chemical (low hydrolysis)

·         Moderate to strong frost weathering

·         Weak biotic weathering

Explanation

·         Therefore of low temperature and low ppt

·         Little chem. Or bio action (some minor chemical from plants’ acid)

·         Variation from temperature around 0^oC frost action on dominant form

·         Little percolation of water restricts chem. action

·         Active carbonation at temp around 0^oC (higher solubility of CO₂ at low temp)

Resultant landforms

·         Fresh rock. Little alteration, angular block, surface features (e.g. patterned ground and frost wedges)

e.g. Alaska in USA

Tropical humid

·         Strong chem. (high hydrolysis & carbonations)

·         Absent or insignificant frost

·         Strong biotic weathering

·         Therefore of high temperature & ppt

·         Active chem. action & plant / animal growth

·         Temp controls level of chem. activities　＆Ppt rate activity

·         Small temp range with minimum above 0^oC reduces phy weathering except by organisms

·         Soil and plant CO₂ to form carbonates

·         Deep penetration of water encourage chem. action

·         Highly alteration rock (10 – 100m), after reduction is deep clay

·         Degrees of weathering restricts penetration along joints to form cliffs, tors and core stones

HK

苔原

描述

·   化學作用很弱（水解作用很少）

·   中等至強烈凍裂作用

·   生物風化很弱

解釋

·   由於低溫及少降水

·   化學及生物作用很少（只從植物酸中提供少量化學風化）

·   最常見為溫度徘徊於零度上下所出現的凍裂作用

·   少降水限制了化學作用

·   溫度接近零度時有活躍的碳化作用（因為CO₂ 在低溫較易溶）

地形

·   新鮮岩，岩層少轉變，呈塊狀，多為地表特徵（如階狀地表及凍原）

e.g. 美國阿拉斯加

熱帶濕潤地

·   強烈化學風化（大量水解及碳化作用）

·   缺乏足夠的結霜作用

·   強烈的生物風化

·   由於高溫多雨

·   化學作用及動植物生長活躍及迅速

·   氣溫控制了化學活動及降雨量的多寡

·   溫差少而最低溫亦高於零度減少了除生物作用外的物理風化

·   土壤及植物的CO₂ 形成碳化合物

·   水的深入滲透促成了化學作用

·   岩層轉化大(10 – 100m), 當表土被移除後為黏土

·   風化程度限制了沿裂綘的滲透，形成懸崖、石塔及核心岩的

HK

Description

7

Comparison (MW, SD)

7, 7

(max 7 if no comparison)

Examples (TRF & TD)

4

In mass wasting:

-          mass wasting = shear stress > shear strength

-          water acts as lubricant, ↑weight of overlying materials = high shear stree

-          water ↓cohesion of soil particles = low shear strength

-          water speed up the downslope movement

-          especially after trigger effect: thunderstorm, typhoon

In slope development

-          effects the types of weathering and the resultant materials to be transported downslope

n           more water will facilitate chem. Weathering (solution, hydrolysis…) → rapid decomposition → fine materials and deep regolith

n           water can create pressure to existing cracks and widen them by phy weathering & breaking down of bigger debris

-          affects the speed, magnitude of transport process

n           more water will fasten the speed of weathered / decomposed materials to slide / flow / fall to lower slope

TRF

-          heavy rainfall (convectional rainfall, typhoon, troughs) as the result of rapid rising air due to ITCZ & equatorial location

-          large interception as luxuriant vegetation under hot wet climate

-          runoff < infiltration as veg acts as obstacles (except under deforested areas)

→abundant water to affect the role of mass wasting and slope dev

TD

-          low R” as at sinking arm of Hadley cell but sudden short-lived heavy R”

-          low interception as little veg under such extreme climate

-          runoff > infiltration ∵ sudden heavy R” may lead to the formation of sheetwash and existence of hard pan in the soil

→the effects of water in affecting mass wasting and slope dev is more significant during sheet wash

Resultant mass wasting

-          landslides, soil creep, mudflow happen in TRF ∵ heavy rain, strong chem. Weathering results in thick regolith

-          worsen esp when the areas are deforested and over steep slopes

-          soil creep is common as alternate wet and dry condition is common which ↑ the instability of slope

-          rock fall takes place as strong phy weathering results in lots of debris and cracks. The presence of water in the cracks will exert more pressure to it

Resultant landform dev

-          steepness: gentler (slope decline)

-          regolith: thick (may > 60m)

-          slope form: roughly follows 9unit slope

-          related features: pediment may dissected to depth of up to 150m, rainsplash after deforestation will lead to rill erosion which eventually leads to the formation of gullies and badland

-          retain steepness (// retreat)

-          thin

-          roughly follows 4unit slope

-          during rainstorms, sheetwash will dissect the slope into gullies and then wadis, together w/ wind & water action, inselberg, mesa/butte is formed. Waterfall, alluvial fan are common at the bottom of dissected slopes

描述

7

比較 (塊體移動，坡面發育)

7, 7

(若無比較，最高7分)

例子 (熱帶雨林及熱帶沙漠)

4

在塊體移動中：

-          塊體移動 = 營力＞阻力

-          水作為潤滑劑，↑上部物料的重量 = 高營力

-          水 ↓土壤粒子的凝聚力 = 低阻力

-          水加速了向下移動

-          尤其是在誘發因素之後：暴雨，颱風

在坡面發育中：

-          影響風化種類及被運送下坡的物料

n           較多水分加促化學風化（溶解，水解…) → 較快的分解作用 → 物料較幼細及風化層深厚

n           水以物理風化形式對裂縫造成壓力並使之擴大並形成較大的岩屑石

-          影響運送的速度及強度

n           較多水分使風化及分解物的傾瀉／流動／崩陷速度增快

TRF

-          位於熱帶輻合帶及赤道位置而帶來暴雨(對流雨，颱風，低壓槽)

-          濕熱情況下豐富的植被帶來大量植物截流

-          表面徑流＜下滲作用，因為植物成為阻礙(除了在伐林地外)

→ 大量水分影響塊體移動及坡面發育的角色

TD

-          位於低緯環流圈的下降翼故降雨較少但有為時短暫的暴雨

-          氣候極端故只有少量植物，植物截留很少

-          表面徑流＞下滲作用，∵突然的暴雨形成表面沖刷，並在土中形成硬瞉

→表面沖刷形成時，水對塊體移動及坡面發育的影響尤為強烈

形成的塊體移動

-          山泥傾瀉，土蠕，泥流，∵暴雨，強烈化學風化形成深厚風化層

-          在伐林地及峭坡上情況更惡劣

-          土蠕因乾濕交替而普遍，↑坡面不穩定性

-          岩崩因強烈物理風化作用而形成，並產生大量岩屑及裂縫。裂縫中的水分對之產生壓力

形成的地形發展

-          坡度：平緩 (坡面遞減)

-          風化層：厚（＞ 60米)

-          坡面形態：9單位模式

-          相關特徵：山麓平原可至150米，伐林後的雨水濺擊作用可形成沖溝侵蝕及劣地

-          坡度保持 (平衡後退)

-          薄

-          4單位模式

-          雨暴時，表面沖刷將坡面切為沖溝，及後形成乾谷，加上風／水作用，會形成島山，孤丘及平頂山。瀑布，沖積扇在坡底普遍可見。