1969-03-22 — Page 23

育教僑華頁三第張六第

CITY

HALL

BIVA=#B2BWAH KIU YAT PARLA

郭日僑華

CC數中學會考試題預習

1969

地理科

(=+)

劉玉領。

GEOGRAPHY (20)

36. (a) The following features ara associated with

rivers: ox-bow lake, levees. For each describe

method of formation.

Explain the term 'river capture".

With reference to one local example descr river capture has taken place.

how

Ox-bow lake:

In the lower course of a raver, the action of running water is almost entirely constructive, Owing to the negligible gradient of the land it passes through and the heavy load of silts it carries, deposition takes place. The valley becomes so open that its sides are barely dis. cernible and the river meanders through the flat land. However, erosion occurs, though on & small scale, in the form of side-cutting rather thân down-cutting. The river begins to swing from side to side in wide loops as it progresses across the flat country. The meander is continually being accentuated by the rivar itsel since on the concave side of a curve the bank Is worn away by the current, whereas on the convex side solid material is deposited. Ultimate. ly the meander may form almost a complete circle, and the river will cut across the narrow strip of land and straighten this part of the course again, leaving an x-bow lake which has a 100se-shoe shape.

Stage

Levees)

erosion

deposi

deposito

ox-bow lake

In the lower course of a river, the current is slowest at the sides and the bottom because of its retardation due to friction. This “ slackening of speed at onse results in silt deposition at the river bed as well as on the two banks. After a long time, the bed of the river raised. The river now flows at a leval higher than the surrounding plains on either side between raised banks or embankments which are known as levees,

Levees

River

deposition.

bigger particles

dropped first and fine particles carried further

(b) River capture rerers to the diversion of the

headwater of one river into the basin of a neighbour with greater erosional activity which is flowing at a lower level. In brief, ons river 1# beheaded by another,

River capture occurs when a powerful stream Guts back into the divide by headward erosion and ultimately reaches the upper course of a weaker adjacent stream, Water in the latter, seeking the lowest level possible, flows into tna

more powerful stream, leaving a sharp bend at the elbow of capture and a wind gap. The remaining part of the r fver that has been beheaded is now known as a miafit. The lan Touan drainage in Hong Kong provides one possible example of rivar

Before Capture

After Capture

Elbow of capture

Wind Gap

Tai

Ans.

Highland

Stream. flow.

How does ice erode the land surface?.

(b) How are hanging valleys ar cirques formmar

(a) Tell concisely the ways in which glaciated

regions can be of value to man, a

(a) What is loess? How does it affect man?

Locate the areas in the world where it occurs.

(a) Ice erosion is of two processes: plucking and abrasion. Plucking refers to the pulling away masses of rock on the valley floor or sides of glacier, by means of ice freezing on to protuberances and detaching them as it moves on. Plucking is particularly marked in the case of well jointed rocks. As a glacier moves along, pieces of rock broken off the valley sides fall onto the glacier and becomes embedded in it. These Function as an abrasive medius leading to the mechanical wearing-down of rocks that lie in their way. This process of wearing away is termed abrasion.

(b) Hanging Valleys.

A hanging valley is a high-lying tributary valley which leads with a marked steepening of slope into a main valley. The stream of this valley joins the main river via a waterfall. There are two entirely different explanations to its origin, One group attributes this to the unequal excavation by a major glacier and a more shallow and therefore leas effective tributary glacier. Consequent to this, the main valley i overdeepened whereas the tributary valley receives little deepening and remins' highly perched above the main valley. Another group holds that most of the deepening must be fluvial and that it has occurred during inter-glacial pariods. They suggest that in a period of ice- retreat, the main valley was unoccupied by ice Whilst the higher parts of the tributary vallays still carried an ice cover and could not be Broded by water. These tributary valleys there fore remained ungraded while the main valley wa3 undergoing active erosion

Before Gladiation

tributary

ley

Girques:

After Glaciation

hanging valleys,

River Valley

waterfall

Main U-shaped

valley

Cirques are steep-sided semi-circular basina of glacial origin high us on mountain slopes They appear to have acted as collecting grounds for the ice which flows down the slopes as valley glaciers. A shallow praglacial hollow his been progressively enlarged, first by alternate thaw-freeze of a anow-patch within it, which causes the rocks to disintegrate, Freeze-thaw eats both into the back wall of the cirque, thum maintaining its steepness, and also into th floor, thus emphasizing its basin shape. It also provides debris which freezes into the base of the ice and so acts as an abrasive. It is a common feature in glaciated mountain ranges, often. containing a corrie-lake known an à tarn,

Before Glaciation

shallow depressions.

After Glaciatic

Cirques (corries)

c) Glaciated regions can be of value to man in my different ways. Firstly, boulder slay deposits are sometimes vary fertile, .g. Fast Anglia in Great Britain and parts of the Dairy Belt and Wheat Belt of North America. The degres of fertility depends largely on the source of origin of the glacial drift. Secunday, old glacial lake beds are invariably fertile, Extensive areas of the Canadian Praires owe their prosperity to the rich alluviume which once collected on the floors of the glacial lakes, Thirdly, waterfalls resulting from glaciation can be harnessed for the generation of hydro-

electric power. Fourthly, some glacial lakas, such as the Great Lakes of North america, help. to regulate the flow of streams and are of real value as natural waterways. Fifthly, many glaciated valleys have benches high up on their sides which provide good summer pasture for cattle so that transhumance is practised in mountainous countries as Norway and Switzerland, Lastly, glaciated mountain regions attract tourists and offer good skiing grounds in winter Tourism can be promoted in these areas.

Loess 18 Wand borne deposit accumulated outside the desert regions. Winds carry fine dust be- yond the desert margins and drop them on neighbouring land areas. In Eurage, loose is known as limon and in the United States as adobe.

六期星日二廿月三年九六九一公年八十五國民華中

1969

( 接第六張第二頁)

文中學話題預習

歷史科 (二十)

ware But the "apanese attack on Kiaochow Bay had violated her neutrality. After Kiäochow fell into Japanese bands, China tried unsuccessfully to limit Japanese military activity. But Japan made even MOTH atartling demenda upon Chine in 1915. She presented Chim with Twenty-One Demands. Japan was seeking the scononic exploitation of China, the expansion of her own territories, and control over China's affair is China would have been transformed into a virtual Japanese protectorate if these demands had been granted. China had no allies she could turn to for assistance, as Britain was engaged in the life-and des struggle with Germany, and the United States was concerned with the sinking of the lusitania by German U-boats. It was therefore natural, if not, inevitable, that she would accept the Demands. But it was said tha this step was a mistake in Japanese policy, as they did not reckon on the violent reaction these demands caused in China, The Chinese became anti-Japanese, and carried out a boycott of Japanese goods. The United States did protest, but mildly, and Japan was in the belief that the U.S. would not use force.

In 1917, China too was urawn labu par Kas vy conflict when the Allies promised to suspend Boxer Indemnity payments if she would join in on their sauc. Bat she was too weak to give the alies ary actun nilitary assistance, although her labourera did zoeful work digging tranches in northern France and Fazopotamia,

The war ended in 1918, and both China and Japan being on the winning side against Germany, were reprezented at the Peace Conference, China had three aims at the Conference: the ending of the unequal treaties, the return of Kisochow, and the release of the obligations imposed on her by Japan in 1915, which could not have been binding as they had been agreed under curess. China's claims were not accepted. bo powers were reluctant to offend Japan, and in any case they had secretly pledged their support in 1917. Besides, if Japas had to give up her privileges in Chins, then the powers, too, would have to relingular theirs. But much later, apan, under pressure, agreed to keep bar promise of returning Kisochow to China, However, the unequal treaties with Germany and Aurtria Wore abrogated. Germans and Austrians were no longer to enjoy extraterritorial rights in China. In future, any treaties signed by China with new nations created dur ding the Peace Conference gave, no such rights to foreigners. China also became a maber of the League. of Nations,

Japan gained much from the First World War. While other industrialized powera were engaged in tl War, apanese goods found an unrivalled market over seas, Industrialists made fortunes almost over- night. There was a tremendous increase in shipbuilding, and Japanese ships were seen at parts where they had not served before. There was a great economic boom in Japan. Her policy of agression in China met with almost no opposition, and she had acquired the strate- gically valuable north Pacific island colonies at little cost. At the Washington Conference in 1921, she had emerged as the third greatest naval power in the world, behind the United States, and Great Britain, No wonder the war years were referred to as Japan's golden years.

Questions for next week:

1. Scrape the circumstances that led to the formation

of the Alliances in Europe between 1870 to 1907.

Describe the part played by the United Stacos, u the main issues affecting the Far East from 18531921.

Losse is porous, friable and easily eroded by rivere. In North China, the loess deposita foach thicknesses of several hundred feet, obliterating the former relief and forming a a low plateau of buff-coloured, unconsolidates and highly porous deposits, in which the streame and rivers cut deep gorges. The soils can supe port heavy crops if adequately watered. But the Loess Plateau of North China is an area of erratic and scanty rainfall. Irrigation is difficult because the river flows at a much lower level than the neighbouring land. Never theless, many of the losse hills are terraced

Tor crops, Irrigation 18 difficult because the rivers flow at a much lower level than the neighbouring land, Roads are cut deep into the plateau surface and people live in houses carved out of the loese cliffe. There Mare loess deposits in Central Europe and parte of the North American Plains, and the Pampas of South America. They are, however, aft oft great thickness. They are generally fertile and as they do not suffer from lack of available water, can readily lead themselves to farming. or pastoral activities.

Loess Regions of the World