Category Geology

People are shouting, “The water is rising. The river has reached the streets! Get to higher ground. It’s a flood!”

A flood happens when water runs over land that is usually dry. Rivers most often flood. Normally, much of the rain that falls on land runs into the nearest river. Water from melting ice and snow also runs into rivers. So, when there is a long, heavy rain, or lots of melting ice and snow, millions of tonnes of water may pour into a river.

Just as a bath will overflow if you keep running water into it, the river soon spills over its banks and floods the land around it.

Some rivers flood regularly. The people who live near them prepare for floods by piling bags of sand along the riverbanks. This keeps some of the water from spilling over the banks.

Sometimes lakes and seacoasts flood. Hurricanes and other bad storms can cause floods along the seacoast. Their strong winds push great waves far onto the land. Soon, much of the shore is underwater.

Picture Credit : Google

High on a mountain, snow melts. Some of the melted snow trickles down the mountainside, finding the easiest path. It is so narrow you could step across it.

Another trickle of water bubbles out from under a rock from underground water called a spring. This trickle joins the melted snow, making a wider, faster-moving stream. It flows down the mountain increasing speed. More streams or tributaries, come together to form a river.

Soil and stones, carried along by the rushing water year after year; cut a groove into the mountainside. The bottom of this groove is the bed of the river. The high sides of the groove are its banks.

The rushing river hurries to the edge of a cliff in the mountainside and falls in a roaring, tumbling, splashing waterfall.

In a steep place near the bottom of the mountain, the fast-moving river has worn away the soft rock. Only bumps of hard rock are left sticking up as the river swirls and foams around them. This part of the river is called the rapids.

Past the rapids, the land slopes gently, so the river moves more slowly. The river leaves the mountain and flows out onto a plain.

Other rivers from other mountains join the first river. Together they become a great, broad river that winds slowly across the plain on its journey to the ocean. If the river overflows its banks, it leaves behind mud, sand, and silt that form a flat area called a flood plain.

At the edge of the ocean, the river’s mouth is often a sort of dumping place. The river carries soil and sand. If the water is calm at the river’s mouth, the sand and soil sink to the bottom of the riverbed. Over time, they pile up and form tiny islands. The river flows around the islands and splits into branches.

Over time, a large piece of land shaped somewhat like a triangle has built up at the mouth of the river. This land is called a delta.

Those first trickles of melted snow have travelled far from the river’s head high on the mountain to its mouth in the ocean.

Picture Credit : Google

The ocean shapes the land

When water pokes its way into the land, it creates many different kinds of bodies of water and land areas. Here are some words used to describe such places.

A bay is a place where a part of the ocean or a lake pokes into the land. Seen from an aeroplane, a bay often looks as if a giant has taken a big bite out of the land and water has come in to fill the hole.

An inlet is a narrow body of water that pokes into a piece of land or runs between islands. An inlet tends to be finger-shaped.

An area of land that is almost completely surrounded by water is called a peninsula. One part of it connects to the mainland.

When waves knock pieces of rock into the water, sometimes they wash up on a beach or settle under the shallow water along a coast. When many pieces of rock collect, a new strip of land called a sand bar or spit rises from the ocean.

 

The ocean meets the land

Often where the ocean touches the land, whether it’s the edge of a tiny island or the coast of a continent, there is a beach.

A beach is a stretch of sand, pebbles, or rocks. The sea makes beaches. Waves crash into a rocky shore for thousands of years, tossing the rocks around and breaking them into pebbles. Then, for hundreds or thousands of years more, the waves grind the pebbles together. In time, the pebbles are ground into tiny grains of sand. Many lakes make beaches this way, too.

You could be out in the middle of the ocean – surrounded by thousands of kilometres of water – and not have any water to drink when you’re thirsty. Why? Because ocean water is full of salt. If you did drink it, it would simply make you more thirsty.

The ocean is salty because rivers dump salt into it. All the rivers that flow down mountainsides and over the land tear loose tonnes of minerals. Most of these minerals are different kinds of salts. The rivers carry these salts to the ocean.

There’s never enough salt in most rivers to make the river water taste salty. But rivers have been dumping salt into the ocean for millions of years. By now, there is enough salt in the ocean to cover all of the land on the earth with a layer of salt hundreds of metres deep!

Picture Credit : Google