PRELIMS REVISION QUIZ (DAY-19)

WHAT CAUSES TIDES ?

Tides are the rise and fall of sea levels caused by the combined effects of

➤ The moon's gravitational pull to a great extent

➤ The sun's gravitational pull to some extent are the major causes for the occurrence of tides.

➤ Another factor is centrifugal force of the earth, which is the force that acts to counter balance the gravity.

The 'tide generating' force is the difference between these two forces; i.e. the gravitational attraction of the moon (primary force) and the sun (secondary force) and the centrifugal force of the earth.

Why does the moon have a greater impact on tides than the sun ?

The ocean tides on earth are caused by both the moon's gravity and the sun's gravity. Even though the sun is much more massive and therefore has stronger overall gravity than the moon, the moon is closer to the earth so that its gravitational gradient is stronger than that of the sun.

BAY OF FUNDY - WORLD'S HIGHEST TIDES

Twice each day, 160 billion tonnes of seawater flow in and out of the Bay of Fundy — more than the combined flow of the world’s freshwater rivers!

Tides in the Bay of Fundy coastal zone reach a peak of around 16 m (50′) — the height of a 5-storey building.

The Bay of Fundy’s tides transform the shorelines, tidal flats and exposed sea bottom as they flood into the bay and its harbours and estuaries.

MONSOON CLIMATE

The word monsoon comes from the
Arabic word "mausim", meaning “season.”

A monsoon is a seasonal reversal in wind patterns over a region.

Monsoon, a major wind system that seasonally reverses its direction—such as one that blows for approximately six months from the northeast and six months from the southwest.

The seasonal wind shift is usually accompanied by a dramatic change in precipitation.

The most prominent monsoons occur in South Asia, Africa, Australia, and the Pacific coast of Central America.

MASCARENE HIGH HEAT SINK

We know that the southwest monsoon derives its name from winds which blow from a south-westerly direction in the Indian subcontinent.

But rarely do we think about the "source" of these winds.

They come from a powerhouse located more than 4,000 kilometres from India.

This powerhouse is known as the Mascarene High.

Mascarene High is a high-pressure region is located between 25°S-35°S and 40°E-90°E near the Mascarene Islands in the southern Indian Ocean.

Normally, this high-pressure region starts forming by mid-April and its position and intensity is closely linked to the strength of monsoon in the Indian subcontinent.

If there is a delay in the formation of Mascarene High, there is also the possibility of a delay in the onset of monsoon in India.

A stronger high pressure will produce stronger monsoon winds.

Winds from Mascarene High head in a north-westerly direction towards the east coast of Africa (Somalia).

Here, the topography of Somalia deflects the winds towards the east.

Also, after crossing the equator, these winds experience the Coriolis Force.

Coriolis Force is a pseudo force which exists only because of the Earth’s rotational effect.

Hence, these monsoon winds get deflected eastwards and now they blow from south-west to the north-east direction.

They split into two branches—the Arabian Sea branch and the Bay of Bengal branch.

In this way Mascarene high impacts the weather pattern in India by creating a way and safe passage for the arrival of monsoon winds in India.

DALMATIAN COAST

Dalmatian coasts are the formed by submergence of mountain ridges with alternating crests and troughs which run parallel to the sea coast.

The Dalmatian coast of Croatia is a typical example.

FJORD COAST

A Fjord is a long, narrow and deep inlet between two cliffs that is connected to the ocean.

Fjords were carved by glaciers, and revealed as the ice masses melted.

Fjord coasts are formed by the submergence of these U- shaped glacial troughs.

These are narrow inlets of the sea into the sea coast bounded by steep and high mountains.

Some of the extraordinarily deep fiords are found in Greenland, Norway and Chile where they are about 1300–1400 m deep.

WHAT IS THE DIFFERENCE BETWEEN A RIA COAST AND A FJORD COAST ?

A Ria Coast is a coast were a former river valley was inundated by the sea.

They occur worldwide, found in all latitudes.

A Fiord Coast is an inundated valley, too, but the valley had been carved by a glacier. These are found in formerly glaciated areas in Scandinavia, Canada etc.

Fjords are found only in high latitudes.

Mixing zones of Cold and Warm Ocean Currents (Grand Banks) and cold water upwelling zones (Peru coast) are the most productive fishing grounds on earth. Why?

Phytoplankton are the primary producers in the marine food chain and hence they are called the ‘grass of the sea’.

Phytoplankton are microscopic, single celled organisms which are able to photosynthesize to produce organic matter from inorganic nutrients.

However, there is a fundamental problem phytoplankton in the open ocean have to face. They need both sunlight and inorganic nutrients (such as nitrate and phosphate) to be able to photosynthesize.

Sunlight is only available in the uppermost layers.

During photosynthesis, the nutrients are quickly used up by phytoplankton so they are not available for long periods in the upper layers under normal circumstances.

To escape this problem the seawater needs to be mixed regularly to bring the nutrient rich deep waters up to the sunlight zone where the phytoplankton can grow.

This is one of the reasons why cold and warm currents convergence zones, where mixing happens by the collision of currents and cold water upwelling zones are very productive.

Furthermore, in surroundings where atmospheric temperatures are often colder than oceanic temperatures, the top layers of the ocean are cooled by the atmosphere.

This increases the density of the surface waters and causes them to sink and therefore causes mixing (nutrient deficient water sinks and nutrient rich water is upwelled).

DOGGER BANK

Dogger Bank is a large sandbank in a shallow area of the North Sea, off the east coast of England. For centuries it has been known as a very productive fishing bank. It was named after the doggers, Old Dutch fishing boats especially used for catching cod.

The Dogger Bank is managed by the United Kingdom, The Netherlands, Germany and Denmark.

GLACIAL EROSIONAL LANDFORMS

1⃣ Cirque/Corrie
2⃣ Glacial Trough
3⃣ Hanging Valley
4⃣ Arete
5⃣ Horn
6⃣ Fjord

HANGING VALLEY

It is a valley carved out by a small tributary glacier that joins with a valley carved out by a much larger glacier.

Hanging valleys are formed when smaller tributaries are unable to cut as deeply as bigger ones and remain ‘hanging’ at higher levels than the main valley as discordant tributaries.

RIBBON LAKE - https://t.me/iaspanti/1969?single

CIRQUE/CORRIE LAKE - https://t.me/iaspanti/1971

LACIAL DEPOSITIONAL LANDFORMS

1⃣ Outwash Plain
2⃣ Eskers
3⃣ Kame Terraces
4⃣ Drumlins
5⃣ Kettle Holes
6⃣ Moraines

OUTWASH PLAIN

When the glacier reaches its lowest point and melts, it leaves behind a stratified deposition material, consisting of rock debris, clay, sand, gravel etc. This layered surface is called till plain or an outwash plain.

DRUMLIN

Inverted boat-shaped deposition in a till plain caused by deposition.

KETTLE LAKES - https://t.me/iaspanti/1967

FINGER LAKES - https://t.me/iaspanti/1970

GRAND BANKS OF NEWFOUNDLAND

The cold Labrador Current mixes with the warm waters of the Gulf Stream here, often causing extreme foggy conditions.

The mixing of these waters and the shape of the ocean bottom lifts nutrients to the surface. These conditions helped to create one of the richest fishing grounds in the world.