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Sekhah Efiaty, S.Pd.

Materi berikut ini merupakan bahan ajar IPS SMP Kelas VII Semester 1 Bab 2 dengan judul  Life in The Preliterate Period in Indonesia


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Sekhah Efiaty, S.Pd.

Jika kalian menginginkan materi SMP kelas VII Semester 1 Bab 1 maka klik materi berikut yang berjudul Forms of The Earth’s Surface

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Sekhah Efiaty, S.Pd.

Perjanjian Versailles ditandatangani oleh German Reich yang diwakili oleh Hermann Müller and Johannes Bell, dan Allies (British Empire, France, Japan, Italy, US, dll) di mana Woodrow Wilson mewakili US, Loyd George mewakili Inggris, Clementeau mewakili Perancis, dan Orlando mewakili Italia.

Isi dari perjanjian Versailles, antara lain :

  1. Jerman menyerahkan daerah Elzas dan Lotharingen pada Perancis
  2. Jerman mengganti kerugian perang
  3. Jerman melepaskan semua daerah jajahan dan diserahkan pada sekutu
  4. Kapal-kapal dagang Jerman diserahkan kepada Inggris
  5. Angkatan perang Jerman diperkecil

Versailles’s Treaty Content :

Legal restrictions

* Article 227 charges former German Emperor, Wilhelm II with supreme offense against international morality. He is to be tried as a war criminal.
* Articles 228–230 tried many other Germans as war criminals.
* Article 231 (the “War Guilt Clause”) lays sole responsibility for the war on Germany, which is to be accountable for all damage to civilian populations of the Allies.

Military restrictions

Part V of the treaty begins with the preamble, “In order to render possible the initiation of a general limitation of the armaments of all nations, Germany undertakes strictly to observe the military, naval and air clauses which follow.” Germany was also forbidden to unite with Austria to form a larger Nation to make up for the lost land

* The Rhineland will become a demilitarized zone administered by Great Britain and France jointly.
* German armed forces will number no more than 100,000 troops, and conscription will be abolished.
* Enlisted men will be retained for at least 12 years; officers to be retained for at least 25 years.
* German naval forces will be limited to 15,000 men, 6 battleships (no more than 10,000 tons displacement each), 6 cruisers (no more than 6,000 tons displacement each), 6 destroyers (no more than 800 tons displacement each) and 12 torpedo boats (no more than 200 tons displacement each). No submarines are to be included.
* The manufacture, import, and export of weapons and poison gas is prohibited.
* Armed aircraft, tanks and armoured cars are prohibited.
* Blockades on ships are prohibited.
* Restrictions on the manufacture of machine guns (e.g. the Maxim machine gun) and rifles (e.g. Gewehr 98 rifles).

Territorial changes

Germany’s borders in 1919 had been established nearly a half-century earlier, at the country’s official establishment in 1871. Territory and cities in the region had changed hands repeatedly for centuries, including at various times being owned by the Austro-Hungarian Empire, Kingdom of Sweden, Kingdom of Poland, and Kingdom of Lithuania. However, Germany laid claim to lands and cities that it viewed as historically “Germanic” centuries before Germany’s establishment as a country in 1871. Other countries disputed Germany’s claim to this territory. In the peace treaty, Germany agreed to return disputed lands and cities to various countries.

Germany was compelled to yield control of its colonies, and would also lose a number of European territories. The province of West Prussia would be ceded to the restored Poland, thereby granting it access to the Baltic Sea via the “Polish Corridor” which Prussia had annexed in the Partitions of Poland. This turned East Prussia into an exclave, separated from mainland Germany.

In Africa, Britain and France divided German Kamerun (Cameroons) and Togoland. Belgium gained Ruanda-Urundi in northwestern German East Africa, Great Britain obtained by far the greater landmass of this colony, thus gaining the ‘missing link’ in the chain of British possessions stretching from South Africa to Egypt (Cape to Cairo), Portugal received the Kionga Triangle, a sliver of German East Africa. German South West Africa was mandated to the Union of South Africa.

In the Pacific, Japan gained Germany’s islands north of the equator (the Marshall Islands, the Carolines, the Marianas, the Palau Islands) and Kiautschou in China. German Samoa was assigned to New Zealand; German New Guinea, the Bismarck Archipelago and Nauru to Australia as mandatory.


Article 231 of the Treaty of Versailles assigned blame for the war to Germany; much of the rest of the Treaty set out the reparations that Germany would pay to the Allies.

The total sum of war reparations demanded from Germany—around 226 billion Reichsmarks—was decided by an Inter-Allied Reparations Commission. In 1921, it was reduced to 132 billion Reichsmarks (then $31.4 billion, or £6.6 billion).

It could be seen that the Versailles reparation impositions were partly a reply to the reparations placed upon France by Germany through the 1871 Treaty of Frankfurt signed after the Franco-Prussian War; critics of the Treaty argued that France had been able to pay the reparations (5,000,000,000 francs) within 3 years while the Young Plan of 1929 estimated that German reparations would be paid for a further 59 years, until 1988. Indemnities of the Treaty of Frankfurt were in turn calculated, on the basis of population, as the precise equivalent of the indemnities imposed by Napoleon I on Prussia in 1807.

The Versailles Reparations came in a variety of forms, including coal, steel, intellectual property (eg. the trademark for Aspirin) and agricultural products, in no small part because currency reparations of that order of magnitude would lead to hyperinflation, as actually occurred in post-war Germany (see 1920s German inflation), thus decreasing the benefits to France and the United Kingdom.

The reparations in the form of coal played a big part in punishing Germany. The Treaty of Versailles declared that Germany was responsible for the destruction of coal mines in Northern France, parts of Belgium, and parts of Italy. Therefore, France was awarded full possession of Germany’s coal-bearing Saar basin for a period. Also, Germany was forced to provide France, Belgium, and Italy with millions of tons of coal for ten years. However, under the control of Adolf Hitler Germany stopped outstanding deliveries of coal within a few years, thus violating the terms of the Treaty of Versailles.

A German author has expressed the view that Germany would not finish paying off its World War I reparations until 2020.

The creation of international organizations

Part I of the treaty was the Covenant of the League of Nations which provided for the creation of the League of Nations, an organization intended to arbitrate international disputes and thereby avoid future wars. Part XIII organized the establishment of the International Labour Organization, to promote “the regulation of the hours of work, including the establishment of a maximum working day and week; the regulation of the labour supply; the prevention of unemployment; the provision of an adequate living wage; the protection of the worker against sickness, disease and injury arising out of his employment; the protection of children, young persons and women; provision for old age and injury; protection of the interests of workers when employed in countries other than their own; recognition of the principle of freedom of association; the organization of vocational and technical education and other measures”[20] Further international commissions were to be set up, according to Part XII, to administer control over the Elbe, the Oder, the Niemen (Russstrom-Memel-Niemen) and the Danube rivers.



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A. Introduction

Valley, area of low-lying land flanked by higher ground. Valleys usually contain a stream or river flowing along the valley floor. Most valleys are connected to other valleys downstream, which ultimately lead down to the coast. The sides of large valleys in low-lying areas are usually gently sloping with an average slope of just a few degrees. In mountainous regions, however, valleys are typically deep and narrow, and the sides have slopes of 35° or more.

Every valley is separated from adjacent valleys by a ridge called a drainage divide. Rain falling on opposite sides of a drainage divide flows in opposite directions toward the bottoms of the adjacent valleys. The area bounded by a drainage divide is called a drainage basin, or, in the United States, a watershed, and it represents all of the land area drained by a valley.

One of the broadest and longest valleys in the world is the Mississippi River Valley, which crosses the United States from north to south. The Mississippi River winds down the center of this valley, and is joined at intervals by other major rivers flowing in their own valleys, such as the Missouri, Ohio, and Tennessee rivers. The deepest valley in the world is a section of the Indus River Valley in Kashmir. As it passes through the western end of the Himalayas, the difference in height between the valley bottom and the top of the drainage divide is about 7000 m (about 23,000 ft).

Some valleys are totally enclosed by higher terrain, and rivers or streams within them may terminate in a lake. Examples of valleys that are wholly surrounded by higher ground and do not open to the ocean include Death Valley in California and the Jordan River Valley in the Middle East.

B. River Valleys

The major agent in forming and shaping most river valleys is the river that runs through it. Rivers shape their valleys by eroding and depositing sediments. The structure of the underlying rocks also plays a role, especially in determining the location of waterfalls and rapids.

1. River Valley Formation

Many early geologists gave little thought to how valleys formed. They assumed valleys formed simply as an accidental result of the uneven formation of the surrounding mountains and hills and that rivers simply flowed through valleys once the valleys had formed. However, this view was challenged at the end of the 18th century by James Hutton, a Scottish scientist. Hutton, who is considered by many to be the father of modern geology, argued that, through erosion, rivers produced the valleys through which they flowed. While erosion by rivers is the main valley-forming process, other processes, such as movement of the earth’s crust and glaciers, also play a role in some cases.

The rate at which a river deepens its valley depends on several factors. One factor is how fast the water flows down the river channel. This will generally reach a maximum where the volume of water flowing through the river is large and the slope of the river channel is steep. Another factor is the resistance of the material through which the river channel is cutting.

At the same time that a river channel cuts down into its valley floor, erosion carries soil and sediment down the valley slopes toward the channel. If a river can easily remove all the material being supplied from the slopes and from upstream, then it can continue to cut more deeply into its bed and increase the steepness of its sides. However, if material is being supplied to the channel faster than it can be carried away, then the excess material accumulates on the valley floor.

Steep-sided valleys are often found in young mountain ranges where the land is still being lifted to create mountains. The steep-sided valleys occur because the uplift tends to increase the channel slope, which in turn causes the river to cut more rapidly into its bed. The Indus River, for instance, maintains its course across the western end of the rapidly uplifting Himalayas by eroding its bed at a rate of up to 1 cm/year (up to 0.4 in/year). Across most of the world, however, uplift is slow or absent. As a result, slopes of most valley floors are low, the erosive power of most rivers is modest, and valley-side slopes tend to be relatively gentle.

2. Longitudinal Profile

A graph of the slope of a river channel at each point along its course is called a longitudinal profile. In most cases, the slope of a river becomes less steep as it flows from its headwaters to the ocean. Slopes as high as 200 m/km (1000 ft/mi) can be found in mountainous terrain, but slopes of about 2 m/km (10 ft/mi) are more typical in the middle section of such valleys. Slopes as low as 2 cm/km (1 in/mi) can be found in rivers close to the ocean.

In most rivers there is a complex adjustment between the amount of material supplied to a river channel and the ability of the river to remove it. A graded river is a river in which each section of its longitudinal profile is just steep enough to transport the load of sediment supplied to it and thereby maintain its slope. In such rivers, there is an equilibrium between the rates that sediments are being deposited and eroded. Rivers are very dynamic systems that respond instantly to changes that affect the equilibrium between deposition and erosion. For example, a mudslide may momentarily disrupt the equilibrium by depositing extra sediment into a river, or a thunderstorm may increase the flow of water, which increases erosion. The river responds to such changes with changes in channel depth, in channel slope, or in the speed of the water, which all act quickly to re-establish an equilibrium between deposition and erosion.

Through the dynamic interplay of erosion and deposition, most rivers develop a longitudinal profile that generally becomes less steep as the river flows from its headwaters to the sea. There are several reasons why the lower stretches of a river are usually less steep than the upper stretches and these reasons have to do with why the lower stretches of a river can still remove its sediment supply even with a shallower slope.

An important factor is that the amount of water flowing in the river increases with each successive tributary that contributes to the flow. As the flow increases, a river is able to transport the same quantity of sediment with a shallower slope. A further factor is the tendency for the size of material being carried by rivers to decrease downstream as particles are weathered and abraded. As the average size of the particles gets smaller, a river is able to transport the smaller particles of sediment with a shallower slope.

Occasionally, the slope of a river changes abruptly along its course. Faulting or a transition from hard rock to soft rock along a river course can cause a sharp increase in the river slope. These increases in slope can lead to the formation of rapids or waterfalls, such as the Victoria Falls on the Zambezi River in central Africa. Sharp decreases in river slope can also be caused by faulting. If a river slope decreases abruptly, sediment will tend to be deposited at this point, which may lead to the formation of a fan-shaped accumulation of sediment called an alluvial fan. These features are particularly common where valleys emerge along faulted mountain fronts, such as along the flanks of Death Valley in California.

3. Floodplains

Except in mountainous terrain, rivers are almost always flanked by floodplains. Floodplains are flat wide deposits of alluvium, river-deposited sediment, on either side of the river channel. During floods, a river overflows its banks and spreads out the sediment near the river to form a floodplain. Floodplains of large rivers, such as those of the Mississippi River, can be flat areas tens of kilometers across. River channels migrate back and forth across their floodplains as alluvium is repeatedly eroded and re-deposited a short distance downstream.

4. Terraces

If the erosive power of a river increases, due to an increase in water discharge or slope, then it will cut down into its floodplain and form a new floodplain lower down. Terraces are flat sections of old floodplains that are sometimes left attached to the side of the valley high above the current floodplain. Occasionally, a river can cut terraces into the underlying bedrock of the valley side.

5. Deltas

Many valleys end in a delta, a fan-shaped accumulation of sediment where the river reaches the sea. Deltas form because the river supplies alluvium more rapidly than it can be removed by the action of waves and coastal currents. Notable examples are the delta of the Nile River, on the Mediterranean coast of Egypt and the delta of the Mississippi River on the Gulf of Mexico.

C. Glacial Valleys

Although most valleys owe their origin to erosion by rivers, other mechanisms can carve valleys in the landscape. In regions cold enough for ice to accumulate, glaciers can be a powerful erosive force capable of excavating spectacular valleys. Such glacial valleys typically have very steep sides and broad flat floors, giving a ‘U’ shape cross-section compared with the ‘V’ shape characteristic of mountainous river valleys. Most of the mountainous areas of North America and northern Europe have glacial valleys that formed during the last Ice Age. Glaciers flowed down river valleys in these regions, leaving steepened valley sides. Yosemite Valley in California is an example of a glacial valley with near-vertical valley walls.

Glacial valleys include several distinctive features. Bowl-shaped valleys, called cirques, result from glaciers cutting into the high mountain peaks at the upper end of glacial valleys. Hanging valleys form where small tributary valleys join a main valley that has been undercut by the glacier. Outwash plains form at the lower end of glacial valleys where the debris eroded by the glacier and carried downstream by streams is deposited.

Glaciers are capable of cutting very deep valleys, in some cases resulting in the valley floor being below sea level. Glacially-deepened valleys near the coast can then become flooded when the ice melts, creating fjords. Norway has several examples of fjords along its coast, including the Sognafjorden and Hardangerfjorden , which extend more than 110 km (70 mi) inland.

D. Crustal Movement Valleys

Crustal movements can also play a direct role in creating valleys. When a crustal block is down-faulted below the blocks on either side, the valley that forms is called a graben. An example of a graben is the Rhine graben in Germany, through which the Rhine River flows. A large graben, or series of grabens, of regional extent is called a rift valley. The Great Rift Valley in Africa extends across the continent from Ethiopia to Mozambique. Rift valleys also run along the center of the mid-ocean ridges, a chain of underwater mountains that runs along the middle of most oceans and is the site of seafloor spreading (see Plate Tectonics; Mid-Atlantic Ridge). A large part of the southwestern United States consists of alternating down-faulted and uplifted crustal blocks. These produce a basin-and-range landscape composed of deep elongated valleys (basins) separated by mountain barriers (ranges) (see Basin: Basin and Range Region).

Valleys can also be produced by folding of the crust. When a section of crust is compressed, it folds up like an accordion into a series of arches and troughs. The arches are called anticlines and the troughs are called synclines (see Anticline and Syncline). Initially, the synclines form valleys, called synclinal valleys. Over the ages, however, the anticlines will tend to erode more than the synclines. Eventually, the anticlines will be lower than the synclines, forming anticlinal valleys. The reason that anticlines erode faster than synclines is that the folding of the crust stretched and cracked the rocks in the anticline, making them susceptible to erosion, whereas the folding of the crust compressed the rocks in the syncline, making them resistant to erosion. The Zagros Mountains in Iran provide examples of synclinal valleys formed in a young mountain belt, and the Appalachian Mountains in the United States provide examples of anticlinal valleys formed by erosion in an old mountain belt.

E. Submarine Valleys

Valleys are also found below sea level on the edge of continents. These features are usually called submarine canyons. Some submarine canyons were formed by river erosion when sea level was lower in the past. Between 5 and 6 millions years ago the Mediterranean Sea dried out several times and the Nile River in Egypt and the Rhône River in southern France cut deep canyons, which were then submerged when sea level rose again. Most submarine canyons, however, are carved by the action of turbidity currents. These are currents of dense, sediment-laden water that periodically cascade down the canyons, scouring as they go.

Contributed By:
Michael A. Summerfield

Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

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A. Introduction

Mountain, name usually applied to region of land that is raised rather steeply above the surrounding terrain. Mountains are distinguishable from plateaus by mountains’ usually limited summit area (mountains are generally much narrower at the top than at the base) and they are distinguishable from hills by mountains’ generally higher elevation. The elevation, or altitude, of a mountain is given as the height of the summit above sea level. Therefore, a mountain with an elevation of 4000 m (13,100 ft) may rise to a level of only 3000 m (9840 ft) above the surrounding land.

Mountains are normally found in groups or ranges consisting of peaks, ridges, and intermontane (between mountains) valleys. Except for certain mountains that occur singly, the smallest unit pertaining to mountains is the range, comprising either a single complex ridge or a series of ridges generally alike in origin, age, and form. Several closely related ranges in a parallel alignment or chainlike cluster are known as a mountain system; an elongated series of systems forms a mountain chain; and an extensive complex of ranges, systems, and chains is known as a belt, or cordillera.

B. Formation

Geologists believe that most mountains are formed by movements in the earth’s crust. The plate tectonics model has helped explain many of these processes. This model describes the crust of the earth as made up of a number of vast plates that move about at the rate of a few centimeters a year leading to the collision and separation of continents and the subsequent development of mountain belts.

Movements that result in collisions between plates tend to raise the crust by faulting, folding, or arching up layers of rock. Movements that result in separation, or rifting, of plates cause some blocks of crust to sink, leaving other blocks to tower above them. Volcanic eruptions also raise mountains, and much of the world’s volcanic activity is concentrated along the active margins of crustal plates. Finally, some ranges of low mountains are created by nontectonic processes, chief among these being the sculpturing effects of erosion, which wears away softer rock and leaves the harder rock.

C. Uplift

Collisions between plates of the earth’s crust trigger various geologic processes that result in crustal uplift. A common process, produced by horizontal compression, is the deformation of crustal strata into folds or wrinkles (see Geomorphology) or the thrusting of vast, thick sheets of rock over one another (see Fault). The Himalayas, for example, were raised by the compression that accompanied collision of the Indian plate with the Eurasian one. Europe’s Alps and Jura Mountains also formed because of horizontal compression, generated in their case by collision of the African plate with the Eurasian one. Similarly, the Appalachian Mountains rose in response to forces caused by repeated collisions between the North American plate and the African and European ones, and most of the Rocky Mountains rose because of the compressive effects generated by collisions between the North American and Pacific plates.

Formation of a basin-and-range structure, best exemplified by the basin-and-range areas in Nevada and Utah (see Great Basin), is the result of movement of rock along faults, or major deep cracks, in the crust of the earth. Occasionally, such movement, called faulting, causes rock bordering on faults to be lifted vertically in great blocks. The raised edges of the blocks then appear as mountains, the depressed edges as valleys. Such mountains are also widely known as fault-block mountains.

A third type of mountain formed by uplifting is called the dome. The dome structure is typified by the Henry and Abajo Mountains in Utah, and by the Adirondack Mountains in New York. These mountains are created by deep-seated intrusion of igneous, or molten, rock that arches the rocks at the surface.

D. Erosion

Rock on the surface of the earth is constantly exposed to erosion. Because rocks of different composition resist erosion differently, areas of relatively hard rock may stand high above areas of softer, more easily eroded rock. Mountains resulting from this erosive sculpturing of the land may be linear in appearance if the resistant rock is the upturned edge of a sedimentary rock unit, flat-topped buttes or mesas if the harder rock is a flat-lying unit, or complex and irregular ranges if the resistant rocks are an uncovered intrusive igneous mass. Portions of the Ozark Plateau (also known as the Ozark Mountains) in Arkansas and Missouri are good examples of mountains created by the forces of erosion.

E. Volcanism

Mountains formed by volcanic action are well known because of their usually isolated occurrence and periodically dangerous aspect. Most spectacular and probably most familiar are the conical peaks composed of lava and volcanic debris, such as Mount Rainier and Mount Saint Helens in the western United States, Mount Erebus in Antarctica, Mount Vesuvius in Italy, and Fuji in Japan. Many of these volcanic mountains have summit craters that still emit steam and debris; others no longer showing signs of volcanic activity may be only dormant, not extinct. Shield volcanoes, typified by Mauna Loa and Mauna Kea in Hawaii, are less spectacular even when quite high, since the physical properties of their formative material have shaped them into broad shieldlike masses that deemphasize their height.

F. Importance

Mountains affect life in many ways. Apart from their mineral, forest, agricultural, and recreational resource value, they exert a significant influence on climate and determine the course of economic or historical trends. Especially high mountain ranges, such as the Sierra Nevada in the U.S., the Andes in South America, and the Himalayas in Asia, markedly affect climate and weather patterns over vast areas of the earth because they stand as barriers to regularly circulating air masses. Moisture carried inland by winds from the Pacific Ocean, for example, is lost in the form of rain and snow on the windward sides of the Sierra Nevada and Andes; the leeward, or inland, side is drier, and the land beyond is frequently arid.

The importance of mountains with regard to the history and economy of various nations can be shown by their influence upon the development of the western United States. The first travelers and settlers, and then the earliest railroads, avoided mountain crossings because of the dangers and costs involved. Later, however, the vast deposits of minerals that became so vitally important to the development of several western states were found exposed principally in mountainous areas, and the lure of “striking it rich” drew people and railroads west despite the hardships encountered in traversing the passes. As a result, transportation routes and patterns, with large populations centered about them, were established; most of these remain today.

The political significance of mountains has been noticeable throughout human history. Mountain barriers with their relatively narrow and easily defendable passes have made various ranges throughout the world natural political boundaries, second in strategic importance only to oceans and seas.

Most of the world’s highest mountains lie in the great Himalayan system and the cordillera stretching through North and South America. The accompanying table includes the highest mountains found on each continent.

See ErosionGeologyVolcano. For additional information, see separate articles on most mountains and mountain systems mentioned.

Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

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A. Introduction

Geomorphology, scientific study of landforms and landscapes. The term usually applies to the origins and dynamic morphology (changing structure and form) of the earth’s land surfaces, but it can also include the morphology of the seafloor and the analysis of extraterrestrial terrains. Sometimes included in the field of physical geography, geomorphology is really the geological aspect of the visible landscape. The science has developed in two distinctive ways that must be integrated in order for the whole picture of landscapes to emerge.

B. Historical Geomorphology

One approach to the science of landforms is by means of historical, cyclic geomorphology. The concepts involved were worked out at the turn of the 20th century by the American geologist William Morris Davis, who stated that every landform could be analyzed in terms of structure, process, and stage. The first two are also treated by process geomorphology, discussed below; but the third, by introducing the element of time, is subject to a far greater degree of interpretation. Davis argued that every landform underwent development through a predictable, cyclic sequence: youth, maturity, and old age.

Historical geomorphology relies on various chronological analyses, notably those provided by stratigraphic studies of the last 2 million years, known as the Quaternary period. The relative chronology usually may be worked out by observation of stratigraphic relationships, and the time intervals involved may then be established more precisely by dating methods such as historical records, radiocarbon analysis, tree-ring counting (dendrochronology), and paleomagnetic studies. By applying such methods to stratigraphic data, a quantitative chronology of events is constructed that furnishes a basis for calculating long-term rates of change.

C. Process Geomorphology

This second branch of geomorphology analyzes contemporary dynamic processes at work in landscapes. The mechanisms involved—weathering and erosion—combine processes that are in some respects destructive and in others constructive. The bedrock and soil provide the passive material, whereas the climatic regime and crustal dynamics together provide the principal active variables.

D. Underlying Dynamics

In geomorphological processes, gravity is an all-pervading, essentially invariable energy factor; a second variable, energy flow is provided by solar radiation. The latter is expressed either as a direct thermal variable or, indirectly, through the hydrologic cycle, which involves evaporation of water from the ocean, atmospheric transport of water, precipitation as rain or snow, and a return to the ocean by various processes. A third energy factor is heat flow from the earth’s interior. Although of a magnitude considerably less than solar energy, this heat flow ultimately is responsible for creating major geological structures such as faults, but rates of change tend to be quite low (usually less than 1 mm per year). Nonetheless, in particular zones—for example, along crustal-plate boundaries (see Plate Tectonics) such as the San Andreas fault—stress may build up until released catastrophically in violent displacements of up to 12 m (40 ft). Locally, heat flow from the interior is concentrated in eruptions of magma (molten rock), which produce a variety of volcanic landforms.

E. Weathering and Erosion

Weathering is often a combination of three processes: the mechanical process, as in the growth of ice or salt crystals or in thermal heating and cooling; the chemical process, as in acid-water solutions that tend to dissolve minerals such as calcite and feldspar; and the biological process, as in the effect of plant roots, which generate both mechanical and chemical energy. Erosion is the dislodging, removal, and transport of material, either in solution or in particle form. The energy to accomplish this may be provided in the form of raindrops, running water, wind, waves, or simply gravity (as in a landslide).

An eroding landmass tends to rise to compensate for the removal of the load, but it eventually stabilizes as land relief decreases and stream gradients decline. The resulting surface, almost flat, is called a peneplain. It may be interrupted, here and there, by isolated hills called monadnocks consisting of rocks especially resistant to erosion. The theoretical base level of such a surface—the ultimate grade of streams—is mean sea level. For a peneplain to form and not be destroyed by renewed erosion, sea level must remain stable for millions of years. However, since the end of the Quaternary Ice Age, 10,000 years ago, sea level has risen hundreds of feet.

Human-induced soil erosion is a feature of the present day and of the last few millennia, because clearing land of native vegetation or excessive grazing by domesticated animals exposes the soil to massive erosion. In this way some 3 billion metric tons of particulate material are washed from the surface of the U.S. alone each year. In undisturbed natural settings, on the other hand—notably in low-relief continental interiors—erosion rates are very slow (except in semiarid areas where thunderstorms produce flash floods). In structurally active belts such as in youthful mountains, which as a rule coincide with plate boundaries that recently collided or rifted, erosion rates may be enormous.

Of all the different processes acting on the earth’s surface, rain and rivers are the most vigorous erosive agents. By contrast, although wave action on a rocky coast is often impressive, the rate of retreat of the shoreline is generally very slow. Sand dunes in the Sahara are also impressive, but the sand is only a relatively thin veneer; and the moraines left by giant continental glaciers are likewise only superficial scrapings of ancient soils. In general, without human interference, the landscape is stable.

Contributed By:
Rhodes W. Fairbridge

Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

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Republic of Indonesia

Republic of Indonesia, island republic of Southeast Asia, constituting most of the Malay Archipelago. Indonesia is the world’s fourth most populous country after China, India, and the United States. More than half the people live on Java, where Jakarta, Indonesia’s capital and largest city, is located. Although the islands are home to more than 100 ethnic groups, most Indonesians are of mixed Malay origins and practice Islam.

Several of Indonesia’s islands hosted powerful trading kingdoms between the 5th and 16th centuries ad. The Dutch took control of the islands in the early 1600s and for three centuries profited from Indonesia’s economy, largely at the expense of the local population. Dutch authority over the islands peaked in the early 20th century. But growing Indonesian nationalism led to a declaration of independence in 1945, and the Dutch finally transferred sovereignty in 1949. The country enjoyed tremendous economic growth in the 1980s and much of the 1990s, partly due to Indonesia’s abundant natural resources and increases in the manufacturing and services sectors. As a result, Indonesia’s middle class grew considerably, but poverty remained widespread. Indonesia plunged into an economic crisis in 1997 that led to significant political changes, including the resignation of President Suharto, who had been in office for more than 30 years. Democratic elections held in 1999 installed a new government.

Indonesia is located south and east of mainland Asia and north and west of Australia. About half of Indonesia’s nearly 13,700 islands are inhabited; all are located in the Indian and Pacific oceans. The islands stretch across 5,100 km (3,200 mi) in the region of the equator, a distance nearly one-eighth of the Earth’s circumference. The main islands of Indonesia are Java (Jawa), Sumatra (Sumatera), and Sulawesi (Celebes). The republic shares the island of Borneo with Malaysia and Brunei; Indonesian Borneo makes up about 75 percent of the island and is called Kalimantan. Indonesia also shares the island of New Guinea with Papua New Guinea; Indonesia occupies the western half of the island, known as Papua (formerly Irian Jaya). The smaller islands of Indonesia include Madura, Lombok, Sumbawa, Flores, and Bali. Indonesia administers the western part of Timor Island. Indonesia controlled the eastern part, East Timor, from 1975 until 1999, when the East Timorese voted for independence. The territory was under the administration of the United Nations from 1999 until 2002, when it officially became an independent republic. Unless otherwise indicated, statistical information up to 1999 in this article includes East Timor.

Indonesia is surrounded by the South China Sea, the Celebes Sea, and the Pacific Ocean to the north, and by the Indian Ocean to the south and west. A stretch of mostly open water consisting of the Java, Flores, and Banda seas divides the major islands of Indonesia into two unequal strings: in the south, the long, narrow islands of Sumatra, Java, Timor, and others; and in the north, the islands of Sulawesi, the Moluccas (Spice Islands), and New Guinea. Each of the major northern islands has a central mountain mass, with plains around the coasts. Puncak Jaya (5,030 m/16,503 ft), in the Sudirman Mountains of Papua, is the highest point in the republic. On the southern islands, a chain of volcanic mountains rises to heights of more than 3,600 m (11,800 ft) and extends from Sumatra in the west to Timor in the east. The highest points are Kerinci (3,805 m/12,484 ft) on Sumatra and Semeru (3,676 m/12,060 ft) on Java.

The most extensive lowland areas are in Sumatra, Java, Kalimantan, and Papua. Over centuries, volcanic flows from the many active volcanoes have deposited rich soils on the lowlands, particularly in Java. Java’s fertile volcanic soils support a large agricultural population. The rest of Indonesia is more sparsely settled but contains most of the country’s mineral wealth, including oil in Kalimantan and Sumatra, timber in Kalimantan, and copper in Papua.

Indonesia’s greatest distance from north to south is about 1,900 km (about 1,200 mi) and from east to west about 5,100 km (about 3,200 mi). The country’s total area is 1,904,570 sq km (735,359 sq mi).

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