What is a dune?

Dune

A dune is a hill or mound of sand drifted by the wind.

A dune is a hill of sand.  Dunes are round along sandy shores of lakes and oceans and in sandy deserts.

They are built by the wind.  At the wind blows, it piles the sand into hills that often look like ocean waves in a vast sea of sand.  A rock or shrub may start a dune.  As the dry sand is carried by the wind it drifts along close to the ground.  When the wind strikes the rock or shrub, it drops some of its load of sand, forming a little hill.

In time the hill blocks more sand and grows into a high hill of sand called a dune.  A very large dune may grow to be 500 feet or more high.

Most of them, however, are much lower.

Dunes change and shift endlessly.

A traveling dune advances in front of the wind as it loses sand on one side and gains it on the other.  Grass and other plants that grow in sand help anchor dunes and keep them from drifting elsewhere.

Photo courtesy:  mccullagh

What causes waves?

Waves

Water waves are caused mainly by the wind.  On a windy or stormy day there are many waves in the water, and on a calm day there are fewer waves.  

This explains what makes most waves in the water.  Winds push up waves on seas, lakes and ponds.  The waves you see on a calm day were started far away.  Somewhere over the ocean winds blew against the water and set it in motion. 

When you watch the waves, the water seems to move forward.  But the water does not actually move forward in a wave at all.  A water wave is mostly the up-and-down motion of the water.  This may be compared to the waves made in a rope by shaking one end of it.  The waves un the length of the rope, but the rope does not move forward. 

When the wave motion of the water reaches the shoreline, the shallow bottom makes the water spill onto the beach.  Sometimes an earthquake or an undersea volcano causes a great, destructive wave to seep in from the ocean like a huge tide.  Most people call these tidal waves.  Scientist call them “tsunami” (su NA me), Japanese word that means “storm wave”.

Photo source:  maui

What is a timberline?

Timberline

Some mountains have trees growing clear to their tops, but on many high mountains there is a line above which trees stop growing.

The place where trees stop growing is called the “timberline”.  Trees don’t grow above it because they cannot survive the freezing temperatures there.

Above the timberline the mountainside is likely to be a cold desert with only patches of lichens, moss and stunted vegetation twisted by the strong winds of the mountain tops.

Here, the bitter cold keeps the water in the ground frozen for much of the year, and bigger plants cannot get enough water.

Just  below the timberline the tall pine forests stand alone.  There tough, needle-shaped leaves can withstand the icy winds and harsh living conditions on the cold mountainside better than the broad-leaf trees can.

The timberline is much higher on some mountains than on others.  It depends on the climate, and latitude. –Johnny Wonder

Photo courtesy:  geography.hunter.cuny

How was the grand canyon formed?

Grand Canyon

One of the great natural wonders of the world is Arizona’s Grand Canyon of the Colorado River.  The whole gorge is 217 miles long and, from rim to rim, 4 to 18 miles wide. 

One of the most amazing things about it is that it was made by a river!  Almost hidden between the canyon walls a mile below, the rushing waters of the Colorado River, with the help of many smaller rivers flowing into it, carved out this great chasm in the course of millions of years. 

Even now, the ceaseless cutting continues to carve deeper into the canyon floor.  Erosion from wind and rain have increased the size of the ever-widening, many-colored rock formations that resemble a fairyland of towering peaks and castles.

Color change with the shifting shadows and the changing light.  The Grand Canyon became a national park in 1919. -Johnny Wonder

Photo courtesy:  pinker.wjh.harvard