DOES THE SEA WEAR AWAY LAND?

Sea waves constantly crash into coasts, crushing rocks and pebbles. Rising waves hurl small rocks onto seaside cliffs, eroding them or tearing away at their base until they collapse. Waves and water currents carry sand and gravel that can alter coastlines. The sea and its waves can certainly wear away the land.

Coastal erosion is the wearing away of the land by the sea often involves destructive waves wearing away the coast (though constructive waves also contribute to coastal erosion).

There are four main processes of coastal erosion. These are corrasion, abrasion, hydraulic action and attrition.

Corrasion is when destructive waves pick up beach material (e.g. pebbles) and hurl them at the base of a cliff. Over time this can loosen cliff material forming a wave-cut notch.

Abrasion occurs as breaking waves, concentrated between the high and low watermarks, which contain sand and larger fragments wear away the base of a cliff or headland. It is commonly known as the sandpaper effect. This process is particularly common in high-energy storm conditions.

Waves hitting the base of a cliff causes air to be compressed in cracks, joints and folds in bedding planes causing repeated changes in air pressure. As air rushes out of the cliff when the wave retreats it leads to an explosive effect as pressure is released. This process is supported further by the weakening effect of weathering. The material breaks off cliffs, sometimes in huge chunks. This process is known as hydraulic action.

Attrition is when waves cause rocks and pebbles to bump into each other and break up.

Credit: internet geography

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HOW DID THE AMAZON RIVER GET ITS NAME?

The Spanish soldiers who explored the region for the first time in 1541 battled native female warriors who fought bravely. The name the invaders gave to the river came from the Persian hamazan, meaning ‘those who fight together’ - also used in Greek mythology for outstanding women warriors.

Before the conquest of South America, the Rio Amazonas had no general name; instead, indigenous peoples had names for the sections of the river they occupied, such as Paranaguazu, Guyerma, Solimões, and others.

In the year 1500, Vicente Yañez Pinzon, in command of a Spanish expedition, became the first European to explore the river, exploring its mouth when he discovered that the ocean off the shore was freshwater. Pinzon called the river the Rio Santa Maria de la Mar Dulce, which soon became abbreviated to Mar Dulce, and for some years, after 1502, it was known as the Rio Grande.

Pinzon's companions called the river El Río Marañón. The word Marañón is thought by some to be of indigenous origin. This idea was first stated in a letter from Peter Martyr to Lope Hurtado de Mendoza in 1513. However, the word may also be derived from the Spanish word maraña; meaning a tangle, a snarl, which well represents the bewildering difficulties that the earlier explorers met in navigating not only the entrance to the Amazon, but the whole island-bordered, river-cut, and indented coast of what is now the Brazilian state of Maranhão.

The name Amazon arises from a battle that Francisco de Orellana had with a tribe of Tapuyas where the women of the tribe fought alongside the men, as was the custom among the entire tribe. Orellana derived the name Amazonas from the ancient Amazons of Asia and Africa described by Herodotus and Diodorus.

Credit: New World Encyclopedia

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HOW MUCH WATER DOES THE AMAZON CARRY?

The Amazon River or River Amazon of South America has a greater total flow than the next six largest rivers combined. It is sometimes known as The River Sea. The Amazon is also regarded by most geographic authorities as the second longest river on Earth, the longest being the Nile in Africa.

The drainage area of the Amazon in Brazil, called the Amazon Basin, is the largest on Earth. If the Basin were an independent country, it would have more than twice the area of India.

The quantity of fresh water released by the Amazon to the Atlantic Ocean is enormous: up to 300,000 m³ per second in the rainy season. The Amazon is responsible for a fifth of the total volume of fresh water entering the oceans worldwide. It is said that offshore of the mouth of the Amazon potable water can be drawn from the ocean while still out of sight of the coastline, and the salinity of the ocean is notably lower a hundred miles out to sea. This mixture of fresh and salt water is known as brackish water.

This quantity of water causes the Amazon to have no clouds above the channel near its mouth. These are usually taken in the morning, when water is colder and land is beginning to be much warmer. Above big rivers (the Orinoco and Caura rivers in Venezuela and many more have the same characteristic), cold waters create a high pressure air mass which make rivers easy to see through clouds. On the contrary, during afternoons, clouds cover most river channels.

Credit: cs.mcgill.ca

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HOW OLD IS THE COLORADO RIVER?

Colorado River, major river of North America, rising in the Rocky Mountains of Colorado, U.S., and flowing generally west and south for 1,450 miles (2,330 kilometres) into the Gulf of California in northwestern Mexico. Its drainage basin covers 246,000 square miles (637,000 square kilometres) and includes parts of seven states—Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California. For 17 miles the river forms the international boundary between the U.S. state of Arizona and Mexico. The river drains a vast arid and semiarid sector of the North American continent, and because of its intensive development it is often referred to as the “Lifeline of the Southwest.”

For more than a thousand miles of its course, the Colorado has cut a deep gorge. Where the river system is joined by lateral streams—the Virgin, Kanab, Paria, Escalante, Dirty Devil, and Green rivers from the west, and the Little Colorado, San Juan, Dolores, and Gunnison from the east—a transverse system of narrow, winding deep canyons has been cut. Each entering river and each lateral creek has cut another canyon, and thus the upper and middle parts of the Colorado basin are traversed by a labyrinth of deep gorges. The longest of these unbroken trunk canyons through which the Colorado flows is the spectacular Grand Canyon, extending from the mouth of the Paria to the Grand Wash Stream. Other canyons cut by the river include Marble Canyon, Glen Canyon, and Cataract Canyon. Canyonlands National Park encompasses another of these regions at the juncture of the Green and Colorado rivers in southeastern Utah.

Credit: Britannica

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HOW OLD IS THE NILE RIVER?

The Nile River flowing through Egypt could be six times as old as previously thought, according to a study which estimated it to have originated at least 30 million years ago. The study, published in the journal Nature Geoscience, assessed the links between the geographical and physical features — or topography — of the Nile River to the flow of molten rocks in the Earth’s mantle.

The researchers, including those from the University of Texas (UT) at Austin in the US, connected the tilted nature of the Nile’s topography to a conveyor belt of mantle rock pushing up against the Ethiopian Highlands in the south, and pulling the surface down in the north. This gentle gradient, they said, keeps the Nile on a consistent northward course from its beginning to the end. The study said the Nile would have turned west long ago — probably changing the course of history along with it — if it weren’t for the mantle movement keeping the river on course.

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