Types of Mountains: Fold Mountains - Simple Notes
- Fold Mountains - Most Common &
Important: These are the most widespread and
most important type of mountain.
- How Fold Mountains are Formed:
- Large-scale Earth Movements:
Created by massive forces within the Earth.
- Stresses in Earth's Crust:
These forces cause stress in the Earth's outer layer (crust).
- Causes of Stress:
Stress can come from:
- Weight of rocks above.
- Movement of hot rock in the Mantle
(below the crust).
- Magma (molten rock) pushing into the
crust.
- Expansion or shrinking of parts of the
Earth.
- Compressive Forces:
These stresses lead to pushing or squeezing forces (compression)
on rocks.
- Folding and Wrinkling:
Rocks are forced to fold and wrinkle along weak areas. Think of
pushing a tablecloth from the sides - it wrinkles up! (See Fig. 18 a
& b in your text).
- Upfolds and Downfolds:
- Anticlines:
Upward folds (like arches).
- Synclines:
Downward folds (like troughs or valleys).
- Complex Folding in Big Mountain Ranges:
- Himalayas, Rockies, Andes, Alps:
Major fold mountain ranges.
- Complex Forces:
Forces that created these were very complicated, leading to more complex
folds.
- Types of Complex Folds (See Fig. 19 in
your text):
- Simple Fold:
Basic upfold (anticline) and downfold (syncline).
- Asymmetric Fold:
Folds are not even on both sides.
- Overfold:
Top of the fold gets pushed over a bit.
- Recumbent Fold:
Fold gets pushed over really far, lying down.
- Overthrust Fold (Nappe):
Extreme case - rock layers fracture (break), and the top part of a
recumbent fold slides over the lower part along a thrust plane (fault
line). The overhanging part is called a nappe.
- Mountains of Elevation:
Fold mountains are raised very high, sometimes miles up, so they are
called "mountains of elevation".
- Volcanic Activity:
Fold mountains are often found in areas with volcanoes. Especially
in the Circum-Pacific region (ring around the Pacific Ocean).
- Mineral Resources:
Fold mountains are rich in minerals like tin, copper, gold, and
petroleum (oil).
In Simple Words: Fold
mountains are like wrinkles on the Earth's surface, made when huge forces push
and squeeze the Earth's crust. Imagine pushing a rug from both ends – it folds
up! The upfolds are mountains, and the downfolds are valleys. Big mountain
ranges like the Himalayas are made of very complex folds. Fold mountains are
tall, often have volcanoes, and are important sources of minerals.