Rocks & Landforms I-3 Notes

Introduction

Physical Weathering Takes place over tens to hundreds of years Processes that take place in the surface environment of the Earth Causes solid rock to be broken down into loose pieces of minerals and rocks

Chemical Weathering Rocks from deep in the Earth (are at higher temperature and pressure) When these rocks are brought near the surface (different chemical environment). The change in conditions makes some of the minerals chemically unstable Some minerals may breakdown chemically

Physical weathering and chemical weathering act together Physical weathering and chemical weathering act together. However, they will be studied separately.

Physical Weathering Breaks rocks apart without changing their mineral composition

Ice Wedging Water seeps into cracks in rocks Temp. drops, water freezes & expands The expansion puts enormous pressure on the surrounding rocks Frozen water acts like a wedge, making cracks wider

After repeated freezing and thawing, the rocks break apart. Expansion and contraction of water also causes potholes in streets.

Plant Roots Plants take root in cracks of rocks Roots become larger and exert pressure Cracks in rocks become larger and rocks break apart

Chemical Weathering Minerals in the rock dissolve in water forming a weak acid (Acid Rain) Acidic water makes some rocks dissolve even faster Rocks made of the mineral calcite (for example, limestone, are most easily dissolved by acidic water Without water, chemical reactions that weather rocks happen slowly

Biological Processes in Weathering Lichens

Lichens (continued) Among the first organisms that establish themselves on bare rocks Produce a diluted acidic solution which break down the minerals in rocks slowly

Weathering of the mineral material in soil Microorganisms are present in the soil in amazingly large numbers

Larger animals, like earthworms and rodents also live in the soil

As plants and animals die, they add organic material to the soil

This organic material decays and is converted into carbon dioxide Carbon dioxide forms more weak acid (carbonic acid) promoting more weathering

The Earth Systems and Weathering

Formation of karst landform

Formed by chemical weathering Carbon dioxide is produced naturally by animals, the use of fossil fuels and the decay of organic matter in soil Some of this carbon dioxide is dissolved in surface waters forming an acid In areas where pure limestone bedrock and lots of rainfall, karst topography often develops

Happens both on rock surfaces and cracks and fractures in limestone, as acidic groundwater percolates downward

Leads to large underground networks of caverns

Sometimes whole blocks of homes will collapse, forming a sinkhole

Copy Chart The Atmosphere The Biosphere The Geosphere The Hydrosphere

In boxes, write how karst topography occurs in each of the four Earth Systems