landforms. Distribution of mid-ocean rift zones on the margins of the continents

Landform classifications

There are several classifications of landforms of the Earth, which have different bases. According to one of them, two groups of landforms are distinguished:

positive - convex in relation to the plane of the horizon (continents, mountains, hills, hills, etc.);
negative - concave (oceans, basins, river valleys, ravines, beams, etc.).

The classification of the forms of the Earth's relief by size is presented in Table. 1 and in fig. one.

Table 1. Landforms of the Earth by size

Rice. 1. Classification of the largest landforms

We will separately consider the relief forms characteristic of the land and the bottom of the World Ocean.

The relief of the Earth on the map of the World

Ocean floor landforms

The bottom of the World Ocean is divided by depth into the following components: continental shelf (shelf), continental (coastal) slope, bed, deep-water (abyssal) basins (troughs) (Fig. 2).

continental shelf- the coastal part of the seas and lying between the coast and the continental slope. This former coastal plain in the topography of the ocean floor is expressed as a shallow, slightly hilly plain. Its formation is mainly associated with the subsidence of individual land areas. This is confirmed by the presence of underwater valleys, coastal terraces, fossil ice, permafrost, remnants of terrestrial organisms, etc. within the continental shallows. Continental shallows are usually distinguished by a slight bottom slope, which is practically horizontal. On average, they drop from 0 to 200 m, but depths of more than 500 m can occur within their limits. The relief of the continental shoal is closely related to the relief of the adjacent land. On mountainous coasts, as a rule, the continental shelf is narrow, and on flat coasts it is wide. The continental shelf reaches its greatest width off the coast of North America - 1400 km, in the Barents and South China Seas - 1200-1300 km. Typically, the shelf is covered with clastic rocks brought by rivers from land or formed during the destruction of the coast.

Rice. 2. Landforms of the ocean floor

Continental slope - the inclined surface of the bottom of the seas and oceans, connecting the outer edge of the continental shoal with the ocean floor, extending to a depth of 2-3 thousand m. It has rather large angles of inclination (on average 4-7 °). The average width of the continental slope is 65 km. Off the coast of coral and volcanic islands, these angles reach 20-40°, and near the coral islands there are angles of greater magnitude, almost vertical slopes - cliffs. Steep continental slopes lead to the fact that in the areas of maximum inclination of the bottom, masses of loose sediments slide down to the depths under the action of gravity. In these areas, a bare sloping bottom can be found.

The relief of the continental slope is complex. Often the bottom of the continental slope is indented by narrow deep canyon gorges. They often visit steep rocky shores. But there are no canyons on continental slopes with a gentle slope of the bottom, and also where there are islands or underwater reefs on the outer side of the continental shelf. The tops of many canyons adjoin the mouths of existing or ancient rivers. Therefore, canyons are considered as an underwater continuation of flooded riverbeds.

Another characteristic element of the relief of the continental slope are underwater terraces. These are the underwater terraces of the Sea of Japan, located at a depth of 700 to 1200 m.

Ocean bed- the main expanse of the bottom of the World Ocean with prevailing depths of more than 3000 m, extending from the underwater margin of the mainland into the depths of the ocean. The area of the ocean floor is about 255 million km 2, i.e., more than 50% of the bottom of the World Ocean. The bed is distinguished by insignificant angles of inclination, on average they are 20-40 °.

The relief of the ocean floor is no less complex than that of the land. The most important elements of its relief are abyssal plains, oceanic basins, deep-sea ridges, mid-ocean ridges, uplands and underwater plateaus.

In the central parts of the oceans are located mid-ocean ridges, rising to a height of 1-2 km and forming a continuous ring of uplifts in the Southern Hemisphere at 40-60 ° S. sh. Three ridges extend northward from it, extending meridianally, in each ocean: the Mid-Atlantic, Mid-Indian and East Pacific. The total length of the Middle Oceanic Ranges is more than 60,000 km.

Between the mid-ocean ridges are deep-sea (abyssal) plains.

abyssal plains- smooth surfaces of the bottom of the World Ocean, which lie at depths of 2.5-5.5 km. It is the abyssal plains that occupy approximately 40% of the ocean floor area. Some of them are flat, others are wavy with a height amplitude of up to 1000 m. One plain is separated from the other by ridges.

Some of the solitary mountains located on the abyssal plains protrude above the surface of the water in the form of islands. Most of these mountains are extinct or active volcanoes.

Strings of volcanic islands above a subduction zone, where one oceanic plate subducts under another, are called island arcs.

In shallow waters in tropical seas (mainly in the Pacific and Indian Oceans), coral reefs are formed - calcareous geological structures formed by colonial coral polyps and some types of algae that can extract lime from sea water.

About 2% of the ocean floor is deep-water (over 6000m) depressions - gutters. They are located where the oceanic crust subducts under the continents. These are the deepest parts of the oceans. More than 22 deep-sea basins are known, 17 of them are in the Pacific Ocean.

landforms

The main landforms on land are mountains and plains.

The mountains - isolated peaks, massifs, ridges (usually more than 500 m above sea level) of various origins.

In general, 24% of the earth's surface is covered by mountains.

The highest point of the mountain is called mountain top. The highest mountain peak of the Earth is Mount Chomolungma - 8848 m.

Depending on the height, the mountains are low, medium, high and highest (Fig. 3).

Rice. 3. Classification of mountains by height

The highest mountains of our planet are the Himalayas, the Cordilleras, the Andes, the Caucasus, the Pamirs can serve as an example of high mountains, the Scandinavian Mountains and the Carpathians are medium, and the Ural Mountains are low.

In addition to the mountains mentioned above, there are many others on the globe. You can get acquainted with them on the maps of the atlas.

According to the method of formation, the following types of mountains are distinguished:

folded - formed as a result of crushing into folds of a thick layer of sedimentary rocks (mainly formed in the Alpine era of mountain building, therefore they are called young mountains) (Fig. 4);
blocky - formed as a result of raising to a great height of hard blocks of the earth's crust; characteristic of ancient platforms: the internal forces of the Earth split the rigid foundation of the platforms into separate blocks and raise them to a considerable height; as a rule, ancient or revived) (Fig. 5);
folded-blocky - these are old folded mountains that have largely collapsed, and then, in new periods of mountain building, their individual blocks were again raised to a great height (Fig. 6).

Rice. 4. Formation of folded mountains

Rice. 5. Formation of old (blocky) mountains

According to the location, epigeosynclinal and epiplatform mountains are distinguished.

By origin, mountains are divided into tectonic, erosional, volcanic.

Rice. 6. Formation of fold-block renewed mountains

tectonic mountains- these are mountains that were formed as a result of complex tectonic disturbances of the earth's crust (folds, thrusts and various kinds of faults).

Erosive mountains - high plateau-like areas of the earth's surface with a horizontal geological structure, strongly and deeply dissected by erosion valleys.

Volcanic mountains - these are volcanic cones, lava flows and tuff covers, distributed over a large area and usually superimposed on a tectonic base (on a young mountainous country or on ancient platform structures, such as volcanoes in Africa). Volcanic cones formed by accumulations of lava and rock fragments erupted through long cylindrical vents. These are the Maoin mountains in the Philippines, Mount Fuji in Japan, Popocatepetl in Mexico, Misty in Peru, Shasta in California, etc. Thermal cones have a structure similar to volcanic cones, but are not so high and are composed mainly of volcanic slag - a porous volcanic rock that looks like ash.

Depending on the areas occupied by mountains, their structure and age, mountain belts, mountain systems, mountainous countries, mountain prices, mountain ranges and uplifts of a smaller rank are distinguished.

mountain range called a linearly elongated positive landform, formed by large folds and having a significant length, mostly in the form of a single watershed line, along which the most
significant heights, with clearly defined ridges and slopes facing in opposite directions.

Mountain chain- a long mountain range, elongated in the direction of the general strike of the folds and separated from adjacent parallel chains by longitudinal valleys.

mountain system- formed during one geotectonic epoch and having spatial unity and a similar structure, a set of mountain ranges, chains, highlands(large area of mountain uplifts, which are a combination of high plains, mountain ranges and massifs, sometimes alternating with wide intermountain basins) and intermountain depressions.

Mountain country- a set of mountain systems formed in one geotectonic epoch, but having a different structure and appearance.

mountain belt- the largest unit in the classification of mountain relief, corresponding to the largest mountain structures, combined spatially and according to the history of development. Usually the mountain belt stretches for many thousands of kilometers. An example is the Alpine-Himalayan mountain belt.

Plain- one of the most important elements of the relief of the land surface, the bottom of the seas and oceans, characterized by small fluctuations in heights and slight slopes.

The scheme of formation of plains is shown in fig. 7.

Rice. 7. Formation of plains

Depending on the height, among the land plains, there are:

lowlands - having an absolute height from 0 to 200 m;
elevations - not higher than 500 m;
plateaus.

Plateau- a vast area of relief with a height of 500 to 1000 m or more, with a predominance of flat or slightly undulating watershed surfaces, sometimes separated by narrow, deeply incised valleys.

The surface of the plains can be horizontal and inclined. Depending on the nature of the mesorelief that complicates the surface of the plain, flat, stepped, terraced, undulating, ridged, hilly, hilly, and other plains are distinguished.

According to the principle of the predominance of existing exogenous processes, the plains are divided into denudation, formed as a result of the destruction and demolition of previously existing uneven terrain, and accumulative resulting from the accumulation of loose sediments.

Denudation plains, the surface of which is close to the structural surfaces of a slightly disturbed cover, are called reservoir.

Accumulative plains are usually subdivided into volcanic, marine, alluvial, lacustrine, glacial, etc. Accumulative plains of complex origin are also common: lacustrine-alluvial, delta-marine, alluvial-proluvial.

The general features of the relief of the planet Earth are the following:

Land occupies only 29% of the Earth's surface, which is 149 million km2. The bulk of the land mass is concentrated in the Northern Hemisphere.

The average land height of the Earth is 970 m.

On land, plains and low mountains up to 1000 m high prevail. Mountain elevations above 4000 m occupy an insignificant area.

The average depth of the ocean is 3704 m. The relief of the bottom of the World Ocean is dominated by plains. The share of deep-sea depressions and trenches accounts for only about 1.5% of the ocean area.

Back forward

Attention! The slide preview is for informational purposes only and may not represent the full extent of the presentation. If you are interested in this work, please download the full version.

Target:

educational:

the formation of students' understanding of the relief of the bottom of the World Ocean, the main forms of relief (shelf, continental slope, island arcs, deep-sea trenches, oceanic basins, mid-ocean islands), factors affecting the formation of relief;

Educational:

development of skills in working with a geographical map;

Educational:

the formation of cognitive interest in the study of geography and the development of curiosity;

Lesson type: combined

Educational and visual material

6th grade textbook, 6th grade atlas, task cards, wall-mounted physical map of the hemispheres, multimedia presentation “Relief of the bottom of the oceans”.

I Introduction

Class organization.

II Checking homework on the topic “Plains and mountains of land” (Slides 1-10)

1. Individually written task (for weak students).

Card #1

1 What is the difference between a mountain and a hill?

2 What is the name of the highest peak on Earth?

Card #2

1 Using a physical map of Russia, give examples of mountain ranges and mountain systems.

2 What is the significance of the plains in human life?

Card #3

1 All irregularities of the earth's surface form:

a) mountains b) plains; c) relief; d) hollows.

2 If in the Caucasus it is Mount Elbrus, then in the Urals it is:

a) Beluga whale; b) Victory; c) Folk; d) Kazbek.

3 Mountains arranged in a row form:

Card number 4

1 High mountains do not include:

a) Ural; b) the Himalayas; c) Andes; d) Caucasian; e) Tien Shan.

2 Mountains arranged in a row form:

a) mountain valley b) mountain system; c) a mountain peak d) mountain range.

3 “In the middle of our country, like a patterned belt, a ridge stretches. A thousand years ago it was called that - the Stone Belt. Rivers flow down from the ridge and to the west - to Europe, and to the east - to Asia. What spine are you talking about?

a) Verkhoyansky; b) the Caucasus; c) the Ural Mountains; d) Tien Shan.

Card number 5

1 Select three elevations from the listed geographical features:

d) Volga; e) Tien Shan;

f) Valdai; g) Sugar.

2 Add.

Shocks and vibrations of the earth's surface caused by ruptures and displacements in the lithosphere are called ......

3 Select three lowlands from the listed geographical features:

a) Central Russian; b) Caspian; c) Amazonian;

d) Volga; e) Baraba; e) Valdai.

2 Individual written task (strong student).

Card #6

1 The height of the highest mountain of Mars is more than 2 times the height of Chomolungma. Why?

2 Determine on which plains the points of the earth's surface are located with geographical coordinates: a) 55 ° N.W; 83°E, b) 15°S. sh.; 48°W

III. Frontal survey

1 What is relief?

(Relief is a set of irregularities of the earth's surface)

2 What are the landforms?

(plains, mountains)

3 Listen to the description and decide what landform the passage is talking about.

“Sharp peaks topped with snow caps shot up high in the sky. In the necklace of glaciers they kept silence for many millennia, broken only by snow storms and landslides...”

(The mountains)

4 What are mountains?

(Mountains are vast areas of the earth's surface, elevated above the plains and having large elevation differences)

5 What are the heights of mountains?

(Low - up to 1000 m, medium - from 1000 to 2000 m, high - from 2000 m)

6 Listen to the description and determine what form of relief A. Maikov's passage tells about.

“In a cart I go through the hills;
Sometimes there are no boundaries for the eyes...
And all the fields on the sides,
And flocks of birds over the fields...
I'm going for a day, I'm going for two -
And all the fields around, fields!”
(Plain)

7 What are plains? What types of plains do you know by the nature of the surface?

(Plains - vast areas of the earth's surface with a flat or slightly undulating surface)

8 Determine which plain is described in the verses:

“And there are fields, again fields.
Sometimes a stream, sometimes a ravine,
And there are fields, again fields,
And in golden waves again
I fly from hill to hill...
(hilly plain)

Plain. Plain.
Neither yar, nor fall,
Plains - to the north,
Plains to the south.
As if he smoothed the mountainous earth
Some kind of giant iron "...
(flat plain)

9 What are the heights of the plains.

(lowlands up to 200m, uplands - from 200-500m, plateaus - from 500m.)

IV Learning new material

Announcement of the topic and setting goals

1 A rebus is made on the slide. (Slide 11) Students solve the puzzle and write the topic in their notebooks. (Slide 12)

2 Lesson plan (Slide 13):

the history of the study of the topography of the bottom of the World Ocean;
landforms of the bottom of the World Ocean;
processes that form the topography of the bottom of the oceans

3 The history of the study of the relief of the bottom of the oceans

a) The first information about the ocean floor was obtained as a result of sounding the depths near the known islands, which was carried out with the help of LOTA (an ancient device consisting of a cable with a sinker at the end). F. Magellan tried - and of course, failed - to get the bottom of the Pacific Ocean using a rope 370 m long. (Slide 14)

b) Modern scientists use the ESOLOTER device to measure depths. This device operates using the effect of ordinary echo. If you shout in the forest, you can hear the scream coming back. So is the echo sounder. The echo sounder consists of a transmitter and a receiver. The emitter emits sound waves. The sound wave reaches the obstacle and returns back. This sound wave is picked up by the receiver. This sound wave is picked up by the receiver. Knowing the signal's travel time to the bottom and the speed of sound in water, you can determine the depth of the ocean at a given point. Knowing how the depths change along the route of the ship, we can conclude that the bottom topography is changing. (Slide 15)

c) The first map of the ocean floor appeared after the round-the-world expedition of the British ship Challenger in 1872-1876. The Challenger expedition disproved the notion that the ocean floor is a flat, sandy expanse dotted with islands. (Slide 16)

d) With the help of bathysphere submarines, bathyscaphes, scientists can study and photograph the topography of the ocean floor. In our time, it has become possible to study the bottom topography with the help of spacecraft. It turned out that in the images obtained from artificial satellites, an underwater relief is visible, “translucent” - through the water column from a depth of hundreds of meters. Data on the composition of the rocks that make up the ocean floor are obtained using deep-sea drilling. In 1968-1971, underwater drilling was carried out in the area of the Azores from the special vessel Gomar-Challenger.

The study of the oceans with the help of modern research methods made it possible to obtain a complete picture of the topography of the bottom of the World Ocean and its structure. (Slide 17)

4 Landforms of the ocean floor

a) We said that the division of the earth's surface into continents and oceans is not accidental, it depends on the structure of the earth's crust. The continental crust consists of 3 layers. The oceanic crust consists of 2 layers. (Slide 18)

The boundary between the mainland and the ocean does not run along the coastline, but much deeper, under water. Part of the continental crust continues under the oceans and is called the underwater margin of the continents. At the base of the oceanic crust is the bed of the ocean. The place of contact between the continental and oceanic crust is called the transition zone. (Working with the diagram)

b) Shelf, or continental shelf, - (from the English. Shelf - the letters "shelf") - a shallow part of the underwater margin of the continents and islands, which has a relatively leveled surface and slight slopes. The lower boundary of the shelf is drawn along the 200 km isobath. On the continental shelf, one can see the continuation of land forms - riverbeds. Its surface is covered with sedimentary clastic rocks brought from the land by rivers or waves formed during the destruction of the coast. Minerals are mined on the shelf - oil, natural gas and some others. Here is the main zone of world fisheries. The shelf has a different width. (Slides 19-21)

The next form of topography of the ocean floor is the continental slope. (Slides 22,23)

Continental slope - part of the ocean floor, transitional from the shelf to the ocean floor. Average depths are from 200 to 3600 m. It has steep slopes, stepped, dissected by canyons (which are a continuation of the river valleys - Hudson, Indus, Congo, etc.) Continental slopes are characterized by increased seismicity, active landslides.

On the underwater outskirts of the continents there are islands, which are called mainland islands.

Task: work with a map of the hemispheres pp. 14-15 of the atlas.

1. Using the depth scale, determine from the map of the hemispheres in which oceans the shelf area is the largest. (In the Arctic - ...... and the Atlantic Oceans - .....).

2. Is the steep continental slope visible on the maps? How did you find it?

c) Between the underwater margin of the continents and the ocean floor there is a transition zone, which has a very complex dissected relief. It includes island arcs and special landforms - deep ocean trenches.

Island arcs - young mountain structures near the outskirts of the continents. Partially protrude above ocean level in the form of mountainous islands and volcanoes. (Slide 24)

Deep-sea trenches - deep (5-11 km) depressions of the ocean floor, stretched for several thousand km. with a width of up to several kilometers, with steep slopes and usually a flat and narrow bottom. They are located on the (oceanic) side of the island arc, repeating its outlines. The Mariana Trench in the Pacific Ocean has the greatest depth - 11022 m. (Slide 25)

Earthquakes often occur in the transition zone; it is here that many active volcanoes of our planet are located.

d) The ocean bed occupies the deep part of the bottom of the World Ocean, that is, more than 70% of its area. The oceanic crust is widespread here. On the bed of the ocean, as well as on land, there are mountains and plains. The plains of the ocean floor are called basins. The basins are separated from each other by underwater ridges and hills. (Slide 26)

The most important discovery in the late 1950s XX century become mid-ocean ridges. They form a single mountain system at the bottom of the World Ocean with a total length of over 60 thousand km, a width of about 2000 km and a relative height of 3-4 km. For example: Mid-Atlantic Ridge, Arabian-Indian, East Pacific Rise.

The highest parts of the mid-ocean ridges rise above the ocean level in the form of volcanic islands (Iceland, Tristan da Cunha, St. Helena, Easter, etc.). In the central part of the MOR there is a fault (divergence of lithospheric plates), which is a gorge with steep slopes. (Slide 27)

Black smokers(Slides 28-30)

(One of the surprises was the discovery of "black smokers" in the 70s of the 20th century. At the bottom of the gorge where magma pours out, the temperature is high. Therefore, the substances dissolved in it begin to interact with each other, forming sulfurous acid. This acid interacts with the erupted magma, as a result, rather high cone-shaped structures appear, inside which the interaction reaction continues.Black clouds form above the cones, rising to a height of up to 150 m

The most amazing thing is that in conditions of complete darkness, and temperatures of 40 o C, in a poisonous environment, various organisms live and feel great - hundreds of species of animals!)

Volcanoes(Slides 31,32)

There are at the bottom of the oceans and individual mountain ranges, and solitary mountains-cones of volcanoes. Volcanoes rising above the water form volcanic islands. Such islands are the Kuril, Canary, Azores (Find them on the map of the hemispheres).

Extinct underwater volcanoes have flat tops. In warm waters, coral colonies settle on the peaks, forming atolls.

atolls(Slides 33-35)

(Atoll is a ring-shaped coral island. It consists of three parts: the outer slope of the reef, the reef platform and the lagoon. The height of the atoll usually does not exceed 3-4 meters above sea level. Atolls are usually formed by fouling a volcanic island with a coral reef that forms a ring belt. Often this is accompanied by subsidence of the volcanic base under water.Atolls can have a variety of configurations and sizes.One of the largest atolls on Earth - Menshikov in the Marshall Islands archipelago - reaches 2336 km 2, of which 92% is in the lagoon, elongated for 300 km. 92 islands of this atoll - 14.5 km ?. Another large atoll - Rangiroy in the Tuamotu archipelago - occupies 1639 km 2, and its 241 islets occupy 43 km 2.)

The relief of the bottom of the World Ocean is represented by three zones: the underwater margin of the continents, the transition zone, and the ocean floor. (Slide 36)

5 Processes that form the topography of the bottom of the oceans. (Slide 37)

The relief of the bottom of the World Ocean, as well as the land relief, is influenced by both internal and external processes. Internal processes - the movement of the earth's crust, earthquakes and volcanic eruptions - are especially pronounced in the transition zone and in the mid-ocean ridges. External processes in the ocean are different from external processes on land. Winds do not blow in the ocean, there are no sudden changes in temperature, animals and plants change little the bottom topography. The main external process that changes the ocean floor is the formation of sedimentary rocks: clastic - on the continental shelf and at the foot of the continental slope, and organic - mainly on the ocean floor (Slide 38).

V Fixing

Crossword "Relief of the bottom of the oceans". (Slides 39-53)

1- what was the name of the ship that explored the bottom of the oceans and mapped it (Challenger)

2 – instrument for studying the topography of the bottom of the World Ocean. The action is based on the principle of measuring the time it takes for sound to get from the side of the ship to the bottom and back.

3 - the underwater margin of the mainland, where you can see riverbeds, clastic rocks brought from land. (shelf)

4- the formation of detrital and organic rocks on the bottom of the ocean, all this ...............processes (external).

5- what is the name of the ocean floor plain (hollow)

6- cone-shaped buildings at the bottom of the gorge (black smokers)

7-old device, consisting of a cable with a sinker at the end (lot)

8-a set of irregularities of the earth's surface (relief)

9 - the largest area and the deepest part of the ocean (ocean bed)

10- which traveler tried to reach the bottom of the Pacific Ocean using a lot (Magellan)

11- ring-shaped coral island (atoll)

12- the ocean in which the deepest trench is located (Pacific)

13- what is the name of the deepest trench of the World Ocean (Marian).

VI Conclusion(Slide 54)

1 The bottom of the ocean, previously inaccessible to study, is now being explored with the help of special vessels, underwater and space vehicles.

2 The largest landforms of the ocean floor are the underwater margins of the continents, the transition zone and the ocean floor.

3 In the relief of the underwater margin of the mainland, a shelf and a continental slope are distinguished. In the transition zone - island arcs, deep-sea trenches. In the relief of the ocean floor - deep plains and mid-ocean ridges.

4 The most complex and dissected terrain is characterized by transitional areas between continents and oceans.

5 The mid-ocean ridges are the most grandiose mountain structure on the planet.

VII Reflection “Chamomile”

There are three daisies on the board: cheerful, neutral, sad. A cheerful daisy means “I am pleased with myself”, a neutral one means “I have questions”, a sad one means “I don’t understand”. Each of the students takes one petal and attaches it to “his” chamomile.

VIII Homework: Paragraph 22, answer questions 1-7. (Slide 55)

The relief of the bottom of the World Ocean is no less complex than on land, but its detailed study is due to the fact that it is hidden by the water column. Irregularities can only be distinguished by examining the depths of the ocean.

Ways to study the relief of the bottom of the oceans

Currently, there are several ways to determine the topography of the bottom of the oceans:

using an echo sounder- a special device that sends sound signals to the bottom; sound, reflected from the surface, rises back, knowing the speed of sound propagation in water, you can calculate the depth and find out the nature of the deep relief;
using underwater vehicles, which directly photograph the ocean floor;
using spacecraft, which are also capable of taking pictures of the underwater floor.

With the help of all these devices, maps of the reliefs of the bottom of the seas and oceans were compiled. The main unit of measurement on them is the depth scale. Such maps are necessary for everyone who is engaged in navigation.

Rice. 1. Relief map of the ocean floor

Forms of underwater relief and components of the ocean floor

Under water, as well as on land, there are large landforms and small ones. You can see underwater plains and seamounts, as well as components of the ocean floor:

underwater margins of the continents;
bed of the ocean;
mid-ocean ridges.

Brief description of the underwater margin of the continents

The boundary between the mainland and the ocean is not on land, but under water. That is why that part of the mainland, which is located under water, is called the underwater margin of the mainland. It is divided into two large parts:

Brief description of the ocean floor

The ocean bed, with depths from 4 to 6 thousand meters, is the central part of the ocean floor, occupying up to 70% of its territory. There are landforms such as

basins - giant underwater plains;
seamounts and mountain ranges;
underwater volcanoes, both active and extinct.

Volcanoes, rising above the water, form entire islands and island systems. Vivid examples are the Kuril Islands and the Hawaiian Islands.

Brief description of mid-ocean ridges

Ridges are the results of the uplift of the earth's crust, which occurred as a result of the collision of lithospheric plates. Most often they are the boundaries of different plates. We can say that the mid-ocean ridge, as it were, divides the ocean bed in half, forming a continuous chain stretching for 70 thousand km.

A fault passes along the axis of the rise of the ridges, forming a gorge, which, as it were, divides the ridge in half. The steeper slopes face the gorge, the gentler slopes face the ocean floor.

The gorge has a depth of up to 3 km, hot springs beat at its bottom, an outpouring of basalt magma is visible. There are volcanoes along the slopes. The height of the ridges is 3-4 km, the width is up to 2 thousand km.

In those places where the tops of underwater ridges come to the surface, islands are formed. For example, Iceland.

There are separate ridges and mountains at the bottom of the ocean. For example, in the Arctic Ocean.

Changing the topography of the ocean floor

The topography of the ocean floor is still changing. This is primarily due to volcanic eruptions and earthquakes. You can learn more about the change in the topography of the ocean floor in the lessons in grade 6.

What have we learned?

The profile of the bottom of the World Ocean is complex, indented. Most of it is the bed of the ocean. The greatest depths are located in the trenches and at the bottom of the gorge of the mid-ocean ridge.

Topic quiz

Report Evaluation

Average rating: 4.2. Total ratings received: 167.

With the help of this video tutorial, everyone will be able to get an idea about the topic "The relief of the bottom of the oceans." You will learn how the relief of the bottom of the World Ocean is studied, who explored it, what it is like. Then the teacher will tell you what the topography of the ocean floor looks like, hidden from us by water.

The formation of the topography of the bottom of the World Ocean occurs under the influence of external and internal forces of the planet. At the bottom of the ocean there is an accumulation of various substances, volcanic eruptions, earthquakes. The relief of the ocean floor is quite diverse.

The main landforms of the bottom of the oceans:

1. Shelf (continental shallow). Its depth is up to 200 meters, this is a continuation of the mainland under water. The shelf areas are rich in fish and many minerals.

Rice. 3. Offshore oil production

2. Continental slope. It is a "cliff" of the mainland under water, here the depths and steepness of the slope change dramatically.

3. Deep sea trench. These are the deepest parts of the World Ocean, they are deep-sea "gorges" up to 11,000 meters deep. The deepest place is the Mariana Trench (more than 11 km).

4. Bed of the ocean. Its depth is from 2500 to 6000 meters. An ocean floor is a "plain" at the bottom of the ocean.

5. Mid-ocean ridge. They represent "mountains", "ridges" under water. Their length can be up to 60,000 km! Mid-ocean ridges can rise above the water to form islands.

Rice. 4. Mid-ocean ridges on the map ()

6. Seamounts. They are separate rises under water at the bottom of the oceans.

Rice. 5. Landforms of the ocean floor ()

Homework

Section 22.

1. List the main parts of the ocean floor.

Bibliography

Main literature

1. Initial course of geography: Proc. for 6 cells. general education institutions / T.P. Gerasimova, N.P. Neklyukov. - 10th ed., stereotype. - M.: Bustard, 2010. - 176 p.

2. Geography. Grade 6: atlas. - 3rd ed., stereotype. - M.: Bustard, DIK, 2011. - 32 p.

3. Geography. Grade 6: atlas. - 4th ed., stereotype. - M.: Bustard, DIK, 2013. - 32 p.

4. Geography. 6 cells: cont. cards. - M.: DIK, Bustard, 2012. - 16 p.

Encyclopedias, dictionaries, reference books and statistical collections

1. Geography. Modern illustrated encyclopedia / A.P. Gorkin. - M.: Rosmen-Press, 2006. - 624 p.

Literature for preparing for the GIA and the Unified State Examination

1. Geography: an initial course. Tests. Proc. allowance for students 6 cells. - M.: Humanit. ed. center VLADOS, 2011. - 144 p.

2. Tests. Geography. Grades 6-10: Teaching aid / A.A. Letyagin. - M .: LLC "Agency" KRPA "Olimp": "Astrel", "AST", 2001. - 284 p.

Additional-full-no-tel-nye re-ko-men-do-van-nye links to the re-sur-sy of the Inter-net network

1. Russian Geographical Society ().

Question 1. How are the irregularities of the earth's surface on a geographical map?

To indicate absolute heights on plans and maps, horizontal lines are used - conditional lines connecting points with the same absolute height. The direction of the slope decrease is shown by short dashes - bergstrokes. The absolute heights of the tops of hills or mountains are shown on plans and maps as a figure with a dot. On physical maps, for greater clarity, coloring of the intervals between contour lines is used to indicate heights and depths. For the heights of the land, shades of green, yellow and brown are used, for the depths of the ocean - shades of blue. The colors that indicate depths and heights are placed next to the frame of the map and are called the scale of heights and depths.

Question 2. What is the absolute height?

Absolute height - the height of any point on the earth's surface above sea level.

Question 3. What forces are involved in the formation of unevenness of the earth's surface?

The formation and development of landforms are actively influenced by two groups of forces: one is the internal forces of the Earth, the main cause of which is due to the deep processes of our planet, the other is external forces arising under the influence of the thermal energy of the Sun.

Question 4. Are all the irregularities of the earth's surface are landforms?

Yes. Landforms - specific irregularities of the earth's surface, which are a surface that encloses a three-dimensional volumetric body and consists of relief elements or simpler landforms. Landforms can be simple or complex, positive or negative, open or closed.

Question 5. What is relief?

The relief is all the irregularities of the earth's surface, which have different sizes, shapes, origins and are formed as a result of the simultaneous action of internal and external forces. Irregularities in the earth's surface are called landforms.

Question 6. Give definitions to the following concepts: mountains, plains, lowlands, uplands, plateaus.

Mountains are highly elevated landforms within which there are significant elevation changes. Plains are vast areas of the Earth's surface with small elevation differences (less than 200 m), that is, equal. They can differ in the nature of the surface, that is, they can be flat and hilly. The lowest plains are called lowlands. Higher plains are called uplands. Their height above sea level is from 200 to 500 m. The most elevated plains are called plateaus.

Question 7. What are the highest mountains on Earth?

The highest mountains on the planet are the Himalayas, located north of the Hindustan peninsula. In this huge mountain range, 13 peaks are more than 8 km high.

Question 8. What are mid-ocean ridges?

Mid-ocean ridges are huge and very complex mountain ranges stretching for tens of thousands of kilometers.

Question 9. How do internal and external forces influence the formation of the relief of our planet?

Internal and external forces are slowly but constantly transforming the planet's topography. Thanks to them, mountains, plains, lowlands, uplands, and plateaus are formed.

Question 10. How are mountains different from plains?

Mountains are huge, heavily rugged areas of the earth's surface that are elevated above the surrounding area. Plains are huge, fairly flat areas of the earth's surface, which are characterized by a slight fluctuation in relative heights.

Question 11. Why does the topography of the ocean floor differ from the topography of the land surface?

Because the ocean floor is less affected by external forces, its topography is affected mainly only by deep forces.

Question 12. How does a mid-ocean ridge differ from land mountains?

Mountain ranges do not have rift valleys like oceanic ones, because they were formed mainly as a result of the collision of plates, and not their separation. In such a collision, the sedimentary layers are compressed and in the form of huge folds bulge up or bend down, forming mountains and valleys. For the same reason, land mountain ranges are not dissected by transform faults, like oceanic ridges.

Question 13. Using a physical map of the world, write down the names of landforms by filling out the proposed table.

Portal for the student. Self-training