Rock Formation: Sedimentary Rocks

• Compaction occurs when accumulating material squeezes grains together
• Cementation is the that process cements minerals coating sediment grains, gluing them into fused rock
• Metamorphism changes rock composition through intense heat and/or pressure
• Solidification is a phase change of matter into a solid
• Weathering is the process that breaks rocks into smaller particles
• Erosion transports sediment from the place of weathering
• Magmatic sources include parts of lava/magma/volcanoes
• The #1 characteristic is silica content which determines how eruptive a volcano is
• Felsic rocks are high in silica content and light, reactive minerals like feldspar
• Mafic rocks are low in silica content and heavy, nonreactive elements like magnesium
• Extrusive rocks have small grains because lava cools rapidly on Earth's surface
• Intrusive (Plutonic) rocks are large grained because magma cools slowly below Earth's surface

Classifying Sedimentary Rocks

• Clastic rocks are formed from mechanical weathering debris, like Conglomerate, Sandstone, and Shale
• Chemical rocks precipitate from solution or settle from a suspension due to evaporation
• Examples include Gypsum, halite, and rock salt
• Organic rocks form from the remains of plants or animals
• Examples include Coal and limestone

Classifying Metamorphic Rocks

• Foliated rocks have a layered or banded appearance from exposure to heat and direct pressure
• Examples include Slate, Schist, and Gneiss
• Non-foliated rocks have no bands or aligned minerals
• Examples include Quartzite and Marble
• Contact Metamorphism occurs when magma is in contact with surrounding solid rock
• Regional Metamorphism changes over large areas of rock
• Other types include burial metamorphism, subduction zone metamorphism, fault metamorphism, hydrothermal metamorphism, and shock metamorphism

Mechanical Weathering

• Mechanical weathering breaks rock down into smaller pieces by physical means
• Common agents include ice, plants and animals, gravity, running water, and wind
• Less pressure on uplifted rock causes Granite exfoliation

Chemical Weathering

• Chemical weathering breaks rocks down through chemical reactions
• Chemical reactions act on the minerals in a rock
• Reactions commonly occur between rock, water, CO2, O2, and acids
• This changes the structure of minerals which leads to the formation of new minerals

Oxidation

• This reaction is with Oxygen
• Oxidation is a process by which elements combine with oxygen
• Oxidation commonly occurs in rock that has iron-bearing minerals
• hematite and magnetite
• Iron combines with oxygen dissolved in water to form iron oxide (rust): 4Fe + 3O2 → 2Fe2O3
• Arches National Park, Utah

Acid Precipitation

• This reaction is with Acid
• Natural rainwater is slightly acidic with a pH of 6.5 due to water + CO2 from air
• Pollution, plus emissions from combustion of fossil fuels, releases nitrogen oxides and sulfur dioxides Reacts with water to form nitric acid, nitrous acid, and sulfuric acid
• Acid precipitation has a pH of 4–5
• Stone lion outside Leeds Town Hall in England was damaged by acid precipitation

Organic Acids

• This reaction is by organisms
• Acids are produced naturally by living organisms
• Examples include Lichens and mosses
• Acids seep into the rock and produce cracks that eventually cause the rock to break apart

Differential Weathering

• Rock composition greatly affects the rate at which rock weathers
• Differential weathering – softer, less weather-resistant rock wears away and leaves harder, more resistant rock behind

Rock Composition

• Limestone, marble, and other rocks that contain calcite weather more rapidly

Amount of Exposure

• More exposure causes faster weathering
• Surface area
• Small pieces have more surface area
• Fractures and joints
• These are natural zones of weakness in rock that increase surface area
• Water can flow through

Climate

• Alternating hot and cold climates increase weathering
• Including ice wedging
• Increased temperature speeds up chemical reactions
• Humid climates increase chemical weathering
• Cleopatra's Needle is an example in Egypt vs NYC central park

Humans, Plants, and Animals

• Plant roots and animals burrow
• Bat guano attracts insects
• Insects and bat guano speed up mechanical/chemical weathering

Erosion

• Erosion is the process by which Earth's surface materials are loosened, dissolved, or worn away and transported by a natural agent like wind, water, ice, or gravity

Gravity and Erosion: Mass Movement Erosion

• Gravity causes rock fragments to move down inclines: Mass movement
• Rock fragments may slowly or rapidly move
• Examples:
• Rockfall , Landslide, Mudflow, Solifluction, Creep

Wind Erosion

• Wind contains energy
• Saltation is movement of sand by short jumps and bounces
• Wind erosion happens everywhere there is wind, but more dramatic in deserts and coastlines
• Fewer plant roots to anchor the sand/soil

Wave Erosion

• Wind produces waves and currents that erode the coastline
• The force of waves can break off pieces of rock
• Includes mechanical and chemical weathering
• Waves force salt water and air into small cracks in the rock
• Beaches form from the deposition of sediments by waves

Glacial Erosion

• Glaciers are sheets of solidly packed ice and snow
• Glaciers are always moving forward
• May recede if melting faster than snow being added
• As a glacier moves, it picks up and carries rocks from the bedrock
• Travels slowly (few cm to km/year)
• Glacial erosion forms:
• U-shaped valleys and grooves in rock

Streamflow

• Streamflow is influenced by gravity

• Erosion and transport of materials depends on velocity

• Gradient/slope and channel characteristics play a role

• Discharge is the volume of water flowing past a certain point in a given unit of time

Channel Characteristics

• Stream encounters friction from the sides and the bottom of its channel
• Friction slows movement
• Shape, size, and roughness of the channel affect the amount of friction

Changes from Upstream to Downstream

• Gradient decreases BUT average velocity increases
• Channel roughness decreases AND water discharge increases
• Includes tributaries (stream that empties into another stream)
• Channel characteristics are smooth, wide, and deep

Base Level

• Base level is the lowest point to which a stream can erode its channel
• Two types:
• Ultimate (sea level) and temporary (local)

Effects of Streams (Transport)

• Dissolved load is in solution
• Suspended load is in suspension
• Bed load is rolling at the bottom
• Determined by competence (largest particles) and capacity (maximum load)

Santa Ana River

• The Santa Ana River has the largest watershed drainage south of the Sierra
• Is highly urbanized and highly regulated
• Is 100 miles long, with 50 tributaries
• Includes a small flow except during winter season

Deposition

• As velocity decreases, competence decreases, and sediment begins to drop out
• Deltas form around lakes and oceans
• Delta = accumulation of sediment formed where a stream enters a lake or ocean

Side note about Deposition

• Deposition is the settling of sediment and accumulation of layers of sediment in one location
• Natural agents that generate most landscapes are water, wind, and ice
• Human activities impact Earth's surface through: Mountains and Valleys, Changing slopes of hills/mountainsides, Concrete river basins, Pavement sealing, Deforestation

Types of Stream Valleys

• Narrow are rapids and waterfalls with a V-shaped valley
• Wide- meanders (side-to-side erosion), cutoffs, and oxbow lakes