Dynamic Earth Exam 3

volcanism, weathering + erosion, sedimentary rocks

Volcanic Activity

range from huge destructive eruptions to quiet splatters

Factor that detirmines eruption characteristics

viscosity of magma

The more viscous the magma…

the greater resistance to flow - sticky

The less viscous the magma…

very fluid - not sticky

Viscosity is detirmined by…

chemical composition, gas content, tempertaure

Chemical Composition

high silica = high viscosity, high silica produces granitic magmas, low silica produces basalt, intermediate produces andesites

Gas Content

dissolved gases increase fluidity + propulsion of magma from vent, fluid magma allows gas to escape easily (gentle eruptions) and high viscous magma traps sticky gases (explosion)

Temperature

high temperatures cause low viscosity

Ejected Material

brocken rock, ash, dust, gas, lava bombs, lava flows

Pyroclastic Materials

pulverized rock - ash, welded tuff, pumice, lapilli, blocks, bombs

Ash Fall

ash ejected into atmosphere that settles to suraface

Ash Flow

cloud of ash and gas that flows along or close to the surface

Lapilli

confined to immediate area of eruption, measures less than 2mm to 64mm, small stones of soldified lava

Bombs

measure more than 64mm, like footballs, twisted, streamline shape

Blocks

measures more than 64mm, large lapilli, angular pieces of rock

Lava Flows

associated with basalts, high temp, low silica

Pahoehoe Flows

smooth lava with twists and braids, low viscosity

aa Flows

jagged, rough, sharp, high viscosity with escaping gases

Gases

dissolved gases held in magma by pressure, release pressure and gases escape, comprises 1-5% of total magma weight, 70% water vapor, 15% CO2, 5% N2, 5% sulfur

Welded Tuff

glassy shards of hot ash fused together

Pumice

solidified lava with gas holes

Volcano

mountainous accumulation of material

Crater

steep walled depression at summit connected to a magma chamber via vent

Fumaroles

secondary vents that only emit gas

3 Types of Volcanoes

shield volcanoes, cinder cones, composite cones (strato)

Shield Volcanoes

broad slightly domed, low viscosity, high temps, low silica, high gas, flows in all directions, small % pyroclastics, slope does not exceed 15°, largest on earth + solar system (Mauna Loa and Kilauea)

Flows usually move slowly and rarely cause fatalities, with the exception of…

lava tubes

Lava Tubes

forms when margins and upper surface solidify, forming a conduit, lava can flow rapidly or for long distances, up to 50 km an hour, empty tunnel is left when eruption ceases and lava drains

Pillow Lava

lava formed when rapidly chilled underwater (upper part of oceanic crust)

Columnar Joints

lava flow ceases moving and contracts, joints are polygonal fractures that extend downwards and outline columns, forces caused by columns open up joints

Basalt Columns Contract When…

cooling

Cinder Cones

huge amounts of pyroclastics, steep slopes from 30-40°, loose materials, in groups or near large volcanoes, high viscosity, high gas, explosions, little damage (paricutin)

Composite Cones (Strato)

intermediate viscosity (andesite), alternating bands of lava flows and pyroclastics, very explosive, large size makes them deadly, not typicaly cone shaped, emits hot gas clouds (mount st helens, vesuvius, pele)

Lahar

killer danger that forms mudflows from melted ice and ash

Lava Domes

aka volcanic domes or plug domes, steep-sided bulbous mountains, form when visocus fesic or intermediate magma is forced toward surface, slow eruptions caused by high pressure, most violent, destrucitve eruptions

Nuee Ardente

mobile, dense cloud of pyroclastic materials, gases, and dust

Calderas

summit of volcano collapses into partially empty magma chamber (crater lake and wizard island)

Fissure Eruptions

flood basalts, lava flows out of rock fissures, no cone is built, lava sreads in all directions, may form columns, very low viscosity (columbia plateua)

Basalt Plateaus

formed by lava flows from long cracks during fissure eruptions, volcanos fail to develop, low viscosity basalt, cover vast areas, only occur in Iceland (columbia plateau, snake river plain)

Intrusive Igenous Features

dikes, sills, laccoliths, batholiths, volcanic necks

Weathering

physical breakdown and chemical alteration of earth materials

Parent Material

rocks and minerals acted on by weathering

Soil

modified weathered materials

Erosion

removal of weathered materials by running water, wind, glaciers, and gravity, deposited as sedimnets, the raw material for sdimentary rock

Sedimentary rock makes up only 5% of the earth’s crust, but covers…

2/3 of earths surface and most of the seafloor

Differental Weathering

occurs at different rates even in the same area and results in irregular surfaces

Mechancial and Chemical Weathering proceed…

simultaneously

Mechanical Weathering

disaggregation of earth materials by physical forces into smaller pieces that retain the composition of parent material

Chemical Weathering

decomposition of rocks by chemical alteration of parent material

4 Main Types of Mechanial Weathering

frost wedging, unloading, thermal expansion, organic activity

Frost Wedging

water expands 9% when it freezes, mainly in mountains, daily freeze cycle, piles of talus build up at mountain base

Unloading (Exfoliation Sheeting)

mainly igenous rock, slabs break off in sheets due to a reduction overlying weight and pressure (half dome and Stone Mountain)

Thermal Expansion

expansion and contraction of rock due to diurnal thermal cycles

Organic Activity

plants, animals, humans, breaking rocks, etc

Chemical Weathering pt 2

dissolved oxygen (oxidation) - oxidized iron (rust), CO2 forms carbonic acid in water, most minerla chemcially weather easily except for quartz - results in quartz beaches only left in harsh environments

Spheroidial Weathering

also causes rocks to become rounded as chemicals attack the larger surface area of a rock with angles

Rates of Weathering Depend on…

particle size, mineral makeup of rock, temperature, moisture/climate

Particle Size

larger surface area = higher rate of weathering

Mineral Makeup of Rock

minerals which crystallize first in the bowen reaction series (olivine - first and quartz = last)

Moisture / Climate

warm and moist = high rate of weathering, cool and dry = low rate of weathering (limestone in acid regions is stable)

Soil Horizon Definition

well-weathered rock material, distinct layers of soil that differ in texture, structure, composition, and color

Layers of Soil Horizons

o - organic matter

a - topsoil

e - eluviation area

b - subsoil

c - regolith

bedrock

Composition of Soil - Mineral Particles

45%

Composition of Soil - Air

25%

Composition of Soil - Water

25%

Composition of Soil - Organic Matter

5% - humus, roots, organisms

Climate is the most important soil formation factor because it…

affects temperature and precipitation

Precipitation Affects…

leaching of soil

Soluble minerals are taken into solution and precipitated in…

horizon b as irregular masses of caliche

Laterite Soil

red soils tha are composed largely of aluminium hydroxides, iron oxides, and clay minerals (found mainly in tropics)

Vegetation depends mostly on…

the surface layer of organic matter

Climate Affecting Rock Type

same rocks yield different soils in different climates, different rocks in same climate yield same soils

Soil fertility depends on…

organisms

Relief

difference in elevation between high and low points in a region

2 ways slope influences soil formation

slope angle and slope direction

Slope Angle

steep slopes have little or no soil

Slope Direction

effects of tempertaure and sunlight on soil

Pedalfer

humid regions with high rainfall, rainfall leaches mineral leaving aluminum and iron at surface, dark and rich good for agriculture, tends to be acidic

Ped = ? Al = ? Fer = ?

soil, aluminum, iron

Pedocal

in semiarid and arid regions, tends to be whiteish, alkaline (grassland)

If you split the country in 2 halves, which side would be pedocal and which side would be pedalfer?

pedocals are western and pedalfers are eastern

Soil Structure Affects…

porosity and permeability

Porosity

the ability of soil to hold air and water in pore spaces

Permeability

ability of water and air to be transported through the soil pores

Both porosity and permebaility influence…

nutrient transport

Soil Conservation Practices

terracing, strip-cropping, crop rotation, contour plowing, no-till planting, windbreaks

Sedimentary Rocks

any rock made of sediment, weathering, erosion, and deposition are fundamental to the origin of sediments

Detrital Sediment

solid particles from other rocks

Chemical Sediment

comes from chemicals derived from rocks that were extracted from solution by inorganic chemical processes or by other activities or organisms

Chemical sediment forms in…

areas where it is deposited

Detrital sediment is transported by…

erosion agents like water, wind, ice some distance from its source

Rounding

sand and gravel particles collide and abrasian wears away sharp corners and edges

Sorting

size distribution of partciles - well sorted = same size and poorly sorted = wide ranges of sizes

Rounding and sorting influence…

how readily groundwater, petroleum, and gas move through sediments and sedimentary rock

Depositional Environment

sites where physical, biological and chemcial processes yield a distinctive sedimentary deposit (mainly coastal)

3 depositional Settings

continental, transitional, marine

There is a distinct relationship between sediment grain size, spatial, and temporal distance from source rocks.

true

Sand has good…

porosity and permeability

Silt has too much…

porosity

Clay has…

good porosity and horrible permeability