Landscape

Rainbows happen when the sun shines through a very fine spray of water, like rain in the air or the spray from a garden hose or even from a waterfall.
The rainbow is colourful because as sunlight travels through the water spray, it splits into a spectrum of colours. All the colours you see in a rainbow are there all the time in normal light, but they are mixed up together so you only see white light.
You can also see the colours of the rainbow by shining light through a prism.

A ridge is a group of mountains or hills that are joined together to make a line rather than being a series of separate peaks. A ridge might also be any other raised line, like the center of an animal's back.

A salt lake is a type of lake that has dried out and nothing remains but a very thick layer of salt. There are many lakes of this kind in the world, most in quite dry areas. When it rains and they fill up again, the water in them is very salty.

The sea, or the ocean, covers most of the world. The sea is a very large amount of salty water, home to many fish. People go sailing on the sea in boats.

The shore is where the land meets the sea.
There are lots of words you can use instead of shore, like coast or beach.

Stalactites are formed when water that has a lot of minerals dissolved in it drips through the roof of a cave and some of the minerals are left behind. Over a long time, the mineral deposits form into spikes hanging from the ceiling of the cave.
Where water drips from a stalactite, stalagmites form.

A strait is a narrow passage of water connecting two seas or two large areas of water.

A summit is the highest point of something, particularly a hill or mountain.
A similar word to summit is peak or apex.

A swimming pool is a place that people have made just for swimming in. They are usually made out of a hole dug in the ground, lined with concrete and tiled. Some swimming pools are above ground, or are inflatable so you have to pump them up with air before you fill them with water.
Swimming pools usually have very clear, pale blue water.

The tides are the rising and falling of the sea because of the pull of the moon and sun on the oceans.
The depth of the water near the coast can change by several metres between high tide and low tide. At low tide a beach may have much, much more sand exposed than at high tide.
The beach in the picture is at low tide. You can clearly see the dark mark on the jetty posts where the high tide comes to.