While walking along the beach today we came across this rock that is a good example of different types of mechanical weathering. We learnt about this in Geography last year so was good to see it in real life.
Let's first figure out what weathering is! Weathering is the disintegration or alteration of a rock in its natural or original position on the Earth's surface through mechanical, chemical, and biological processes.So, if a rock is changed or broken but stays where it is, it is called weathering.
Now we need to learn about mechanical weathering! Mechanical Weathering is also known as physical weathering, and happens when a large rock is disintegrated into smaller pieces of rock without experiencing any change in its chemical composition. There are five types of mechanical weathering:
- Freeze-thaw weathering happens when water seeps into cracks of the rocks, freezes and expands, gradually breaking the rock apart into pieces. This expansion leads to the cracking of the rocks from inside and eventually after repeated cycles breaks them apart.
- Exfoliation weathering is the term used to describe the peeling away of sheets of rock millimeters to meters in thickness from a rock's surface and occurs when cracks develop parallel to a rock's outer surface.
- Thermal Expansion weathering is when rocks are repeatedly heated and cooled resulting in the expansion and contraction of the rock. This continual expansion and contraction cause the rocks to weaken and eventually break into pieces.
- Abrasion weathering can be caused by either moving water as particles in the water collide against the rock or by winds which carry pieces of sand that collide against the rock and have the capacity to break the rock when they sandblast its surface.
- Salt weathering happens when a saline solution enter the cracks in a rock and evaporate, leaving behind salt crystals. When the temperatures rise, the salt crystals get heated and start to expand and release pressure on the rock, causing it to break.
- Anthropogenic weathering - this is man made weathering and it can be physical or even chemical (if there is man made chemicals washing over the rock)
Now that you've learnt what weathering, mechanical weathering and the different types of mechanical weathering are you should be able to look at the rock in front of you at the GZ and answer these questions:
1) Facing the sea, name the two main types of mechanical weathering that have occured on this rock and state where on the rock they are.
2) Based on your answers above, which one of these two forms of weathering is having a greater impact on this rock and why do you say so?
3) Have a look at the right hand side of the rock. There are two deep holes, do you think these are as a result of mecahnical weathering? Is so which type? How, in your opinion, do you think these were formed?
4) Optional: Write your geocaching name in the sand in front of the rock and upload a pic with your log.
Please submit your answers via the geocaching app within 14 days of logging. If no answers are sent your log will be deleted.