weathering, rocks, rivers

Weathering

The breaking down of rocks and other materials on the Earth's surface.

rock cycle

an idealized cycle of processes undergone by rocks in the earth's crust,

Igneous Rocks

Solidification of magma and lava. Either extrusive or intrusive. Extrusive forms on the outside of the earth's crust and intrusive form on the inside of the earth's crust.

characteristics of Igneous Rocks

- light or dark colored

- classified by texture or composition

- made of mineral crystals of different sizes

types of Igneous Rocks

- granite

- obsidian

- basalt

Metamorphic Rocks

Earth's movement heats rock and shapes and forms the. Igneous and sedimentary rocks heat up and cause a chemical change in their minerals and formation.

types of Metamorphic Rocks

- sandstone becoming quartize

- shale becoming slate

- limestone becoming marble

Sedimentary Rocks

Rock remains, minerals, plant and animal remains are all compacted to make sedimentary rocks. Weathering breaks down rocks and sediments are them transported by erosion. Then go through the rock process cementation which make sedimentary rocks.

Erosion

the removal of solids (sediment, soil, rock and other particles) in the natural environment.

characteristics of Sedimentary Rocks

- composed of pieces cemented together or pressed together

- color variety

- pores between pieces

types of Sedimentary Rocks

- sandstone

- limestone

- shale

TYPES OF WEATHERING

- Physical/ Mechanical Weathering

- Chemical Weathering

- Biological weathering

Physical/ Mechanical Weathering

Any process that breaks rock down into smaller pieces without changing the chemistry of the rock; typically wind and water.

types of physical weathering

- Freeze- thaw

- Exfoliation

- Salt crystallisation

- Pressure release

Freeze-thaw

occurs when water continually seeps into cracks, freezes and expands to about 9-10° in volume, eventually breaking the rock apart.

Exfoliation (heating and cooling)

bare rock is repeatedly heated and cooled. During the day as the rock heats up the outer layers expand and then at night the rock cools and the outer layers peel off like an onion

Salt crystallisation

the decomposition of rock by solutions of salt

Pressure release

overlying rocks are removed by erosion causing underlying rocks to expand and fracture

Chemical Weathering

caused by rain water reacting with the mineral grains in rocks to form new minerals and soluble salts. These reactions occur water is slightly acidic. it occurs in places with warm, moist climates

types of chemical weathering

- oxidation

- hydrolisis

- carbonation

- hydration

oxidation

breakdown of rock by oxygen and water, often giving iron-rich rocks a rusty-coloured weathered surface.

hydrolisis

the breakdown of rock by acidic water to produce new minerals and soluble salts.

carbonation

Carbon dioxide reacts with certain types of rocks forming a solution that can easily be carried away by water.

hydration

minerals absorb water, expand and change the rocks composition

Biological

occurs when tree roots penetrate and widen cracks in a rock or acid released by dying vegetation, attack the rock.

Factors that affect the rate of weathering

- CLIMATE

- SURFACE

- ROCK COMPOSITION

- Relief/topography

- Vegetation (affected by and closely related to climate)

- rock texture

- Rock structure

- Temperature

CLIMATE

The amount of water in the air and the temperature of an area are both part of an area's climate.Weathering occurs fastest in hot, wet climates. It occurs very slowly in hot and dry climates.

SURFACE area

weathering occurs on exposed surfaces of rocks and minerals. The more surface area a rock has, the more quickly it will weather. When a block is cut into smaller pieces, it has more surface area. So, therefore, the smaller pieces of a rock will weather faster than a large block of rock

ROCK COMPOSITION

refers to the proportions of different chemicals making up the rock, and thus the proportion chemicals affects the proportions of different minerals constituting the rock.

rock texture

- coarse grained -> individual minerals can undergo selective chemical attack

- fine grained -> crystals are more tightly bonded thus increasing their strength and coherence BUT crystal boundaries provide potential lines of weaknesses that may be exploited by weathering

- usually fine-grained rocks weather more quickly than coarse-grained ones

Rock structure

- refers to the presence of joints and cavities

- Provide agents of chemical and physical weathering access into rock masses

- Exposes the subsurface portions of rock to agents of weathering -> allowing weathering to take place not just on the surface/near the surface, but deep underground as well as in the Deep Weathering

River processes

- Surface runoff

- Throughflow

- Precipitation

- Groundwater

- Evapotranspiration

- Interception

- Groundwater flow

- Percolation

- Infiltration

- Surface storage

- Soil moisture

- River channel flow

- River runoff

rivers

a large natural stream of water flowing in a channel to the sea, a lake, or another such stream.

hydrological cycle

continuous movement of water on the Earth between the land, sea and air. It is powered by the Sun.

- it is a closed system

closed system

no water is added or lost

Drainage basin

the area of land drained by a river

Catchment area

the area within the drainage basin

Watershed

edge of highland surrounding a drainage basin. It marks the boundary between two drainage basins

Source

beginning or start of a river.

Confluence

point at which two rivers or streams join.

Tributary

stream or smaller river which joins a larger stream or river

Mouth

point where the river comes to the end, usually when entering a sea.

How does the water cycle work?

Water evaporates from oceans and rivers because of the heat from the sun, this process is called EVAPORATION. Water that exits the leaves of plants and trees also rise up into the atmosphere this process is called TRANSPIRaTTION. As the water goes higher in the atmosphere, it gets colder and the water CONDENSES and turns into clouds. As the water droplets gather and become heavier PRECIPITATION occurs. Water RUNS OFF the land and into oceans and rivers and the process repeats.

Precipitation

process by which water falls to the earths

surface.

Interception

process by which precipitation caught/stored by the trees and does not reach the ground

Throughflow

water that either falls through gaps in the in the vegetation or drops from the leaves, stem, twigs

Evaporation

process by which liquid or solid turns to gas /water vapour and rises after heating

Albedo

the reflectivity of a surface

Condensation

process by which water vapour turns back into water droplets after cooling

Transpiration

process by which water vapour is transferred from vegetation to the atmosphere

Evapotranspiration

process by which water is transferred from both water and trees

Surface runoff/ overland flow

water flowing over the surface of the land (streams, rivers etc).

- Occurs in 2 ways:

-When precipitation exceeds the infiltration

-When the soil is saturated

Infiltration

process by which water soaks into the soil layer/ ground.

- Infiltration capacity = is the maximum rate at which rain can enter the soil

Groundwater

water stored in the rocks below the soil layers, aquifers exists here.

Groundwater flow

water slowly making its way towards the sea thorugh the rock layers.

Percolation

process by which water seeps through the cracks in the rocks

Hydraulic Action

process involves the force of water pushing air into the cracks of the beds and banks which forces them apart

Abrasion

process by which the bed and banks are worn down by material in the river (load).

Attrition

Material (the load) carried by the river bump into each other and so are broken down and smoothed

Corrosion

chemical action of river water. The acids in the water slowly dissolve the bed and the banks.

meanders

A winding, looping curve in the course of a river on soft, flat flood plain

As the water flows through a meander the following things occur

- Most water is directed towards the outside of a bend

- This means it flows faster around the outside bend

- It therefore has more energy and erodes the outside bend

- This means it is deeper and has steeper banks called a river cliff

- As most of the water is directed to the outside bend, the inside bend has less water

- Less water means that it is shallower and slower and therefore has less energy

- It therefore deposits (drops) material on the inside bend

- This builds up to form a slip off slope

Ox Bow Lakes/C shaped lakes

formed when meanders continually erode.