Day: August 5, 2019

Rivers

| Sharulatha Neru

Some rivers begin high up in mountains, where snow collects and melts. Some rivers begins where underground springs bubble up to the surface. All rivers run downhill, carrying fresh water to the sea.

river erosion

A river gradually erodes the land it crosses. It slowly carves a V-shaped valley as it travels, wearing down rock and earth and carrying the particles in the waters. One of the best examples of a river changing the landscape is the Grand Canyon in the Colorado, USA. It has taken around 17 million years for the Colorado River to carve the canyon from rocks.

Photo by David Ilécio on Pexels.com.

Creating new land

A river slows down as it gets nearer to the sea and the ground becomes flatter. When a river slows the particles of earth and rock it is carrying drop to the bottom as sediment, creating mudflats and islands. Sometimes these spread out at the river’s mouth in a wide area called a delta. The Ganges and the Brahmaputra rivers meet in India and Bangladesh to form the world’s largest delta, stretching over an area of 105 000km.

the world’s waterfalls

If a river reaches a very hard band of rock, it will wear down the softer rock on the other side and end up plunging down as a waterfall. The world’s highest waterfall is the Salto Angel Falls in Venezuela, which plunges 807m over a cliff. One of the world’s largest falls is Victoria Falls on the African Zambezi River. Over time the Zambezi has carved out a channel around, 1 007m wide.

FACTS…FACTS…FACTS!!!

Top five rivers in order of length

  1. Nile River, Africa (6 696km)
  2. Amazon River, South America (6 400km)
  3. Yangtze River, Asia (6 240km)
  4. Mississippi River, North America (6 192km)
  5. Ob River, Russia (5 534km)
Photo by Mads Thomsen on Pexels.com

EARTHQUAKES

| Sharulatha Neru

Earthquakes causes the ground to shake, and occur when there is a sudden movement in the Earth’s crust. They happen in areas where two of the Earth’s plates meet under the ground

Earthquakes closely follow the borders of the Earth’s plates.

earthquake areas

Most earthquakes occur around the edges of the Pacific Ocean or in mountainous areas such as the Himalayas. It is here that the plates under the Earth’s surface are pushing or sliding the most. Scientist monitor these areas to try to predict earthquakes, measuring for possible warning signs- such as minor tremors that might build up to a larger event.

measuring earthquakes

Instruments called seismographs measure earthquakes. A seismograph detects the shock waves produced and displays a line that records how strong each wave is.

FACTS…FACTS…FACTS!!!

The Richter Scale has 10 numbers representing the energy produced by an earthquake. Each number represent 10 times more energy than the previous number.

SCALE EFFECTSFREQUENCY
0 – 2.0 Not Felt 8 000 a day approx.
2.0 – 2.9 Not felt but recorded 1 000 a day approx.
3.0 – 3.9 Felt but no damage 49 000 a year approx.
4.0 – 4.9 Felt slightly indoors 6 200 a year approx.
5.0 – 5.9 Weak buildings might fall800 a year approx.
6.0 – 6.9 Destructive up to 160km away 120 a year approx.
7.0 – 7.9 Severe damage in large area 18 a year approx.
8.0 – 8.9 Severe damage over 1 000km 1 a year approx.
9.0 – 9.9 Devastation up to 10 000km 1 in 120 years approx.
10 Has never been recorded
Shows seismograph readout.