Water and Weathering

1
Water and Weathering
2
What effect does water have on rocks?

• Rocks get worn away. Look at the pictures of
  gravestones. They are both made from the same
  rock. One of them is about 80 years older than
  the other.

3
Which of the gravestones is older?
4
(No Transcript)
5
One of the things that causes rocks to wear away
is rainwater. Look at the picture of a cathedral.

• The rain has worn away the rock that it is made
  from

6
How does rainwater affect rock?

• Rainwater is acidic. As it falls through the
  air, gases dissolve in the water that make it
  acidic. Rainwater reacts with some minerals in
  rocks, but not others.

7
Look at the picture below

• Why do the rocks in the picture have such strange
  shapes? And who is the hot babe?

8
These shapes have happened because the acidic
rainwater has -

• Reacted with some of the minerals in the rock and
  not others. Some parts of the rock became weak
  and crumbled away.

9
How do we get caves?

• Limestone is a rock made from a mineral called
  calcium carbonate. Acidic rainwater reacts with
  calcium carbonate very easily. The rainwater
  seeps into cracks in the limestone. It reacts
  with the limestone, wearing it away until it
  leaves a cave.

10
Some of the best caves in the world are in areas
of limestone!
11
Rainwater reacts chemically with rocks in other
ways too.

• Rocks that contain iron can turn red when rain
  falls on them. This picture shows rusty rocks.

12
What is weathering?

• Weathering is a word that means rocks have
  changed. Rainwater causes chemical weathering.
  In chemical weathering, new substances are made.

13
Copy these sentences and fill in the spaces using
the words below

• minerals weathered acidic
• Rainwater is slightly______. It can react with
  the rock and dissolve some of the _______ in
  rock. Limestone is easily _____ by acidic
  rainwater.

14
Key Points

• Rainwater is slightly acidic. It can dissolve
  some of the minerals in rocks, and react with
  others.
• Rainwater causes chemical weathering.