Geology Exam 3

magma

all eruptions involve

Mafic basaltic lava

low silica and gas, erupt at high temp

Felsic rhyolitic lava

high silica and gas, erupt at lower temp

Andesitic lava

intermediate lava

Viscosity

measure of fluids mobility

Effusive eruption

non violent, fluid mafic lavas, caused by dissolved gases, lava fountains common, can last weeks, months, years

Explosive eruption

highly viscous magma, gas bubbles get trapped, eruption columns

Eruption column

particles of fragmented lava and gas expelled at supersonic speed

90%

__ of lava is mafic basaltic

<10%

__ of lava is intermediate

1%

__ of lava is felsic rhyolitic

Aa flows

surfaces of rough jagged blocks

Pahoehoe flows

smooth surface, resemble twisted braids of rope

Lava tube

cave-like tunnels, often form in pahoehoe flows, previous conduits for lava

Block lavas

andesitic, rhyolitic, short prominent flow, massive detached blocks on upper surface

Pillow lavas

form from outpourings of basaltic lava underwater, outer skin freezes quickly, interior lava breaks through and squeezes out, composed of tube-like structures stacked on top of each other

pyroclastic materials

pulverized rock and lava fragments ejected from volcanoes, also called tephra

lapilli or cinders

walnut sized pyroclastic materials

blocks

hardened cooled lava, >2.5 inches in diameter

bombs

ejected as hot lava, >2.5 inches in diameter, streamlined shape from hurtling through air

Pumice

light grey or pink porous rock from frothy andesitic and rhyolitic lava

Scoria

reddish brown porous rock from frothy basaltic lava

fissure

crack developed in Earths crust as magma moves forcefully toward the surface

conduit

a somewhat pipe-shaped tunnel

vent

the surface opening of a conduit

volcanic cone

the cone-shaped structure created by successive eruptions of lava and pyroclastic material

crater

funnel shaped depression at summit of most volcanic cones, generally <1km in diameter

caldera

large circular depression >1km in diameter, produced when summit area collapses

parasitic cones

flank vent that emits lava and pyroclastic materials

fumaroles

a flank vent that emits gas

shield volcanoes

broad, slightly dome shaped, large area, begin on seafloors as seamounts, ex. Hawaiian Islands, Canary Islands, Galapagos, Easter Island

cinder cones

eject basaltic lava fragments, steep slope angle, 30-300m tall, frequently in groups, extensive lava fields - final stages of volcano’s life, ex. Paracutin, in Mexico

composite volcano

large, classic shaped volcano, composed of interbedded (generally andesitic) lava flows and layers of pyroclastic materials, many are located adjacent to the Pacific Ocean in the Ring of Fire, ex. Mt St Helens, Fujiyama

pyroclastic flows

mixture of hot gases infused with incandescent ash and larger lava fragments, also called nuee ardente, propelled by gravity, move like snow avalanche, material propelled from vent at high speeds (can exceed 100kmph or 60 mph), typically generated by the collapse of tall eruption columns

surge

small amount of ash separates from main body of pyroclastic flow, can knock over buildings and move cars, ex. St. Pierre-Mt. Pelee, and Pompeii-Mt. Vesuvius

Lahars

mudflow on active or inactive volcano, volcanic debris become saturated with water and rapidly moves down volcanic slope, can be triggered when magma nears surface causing snow and ice to melt, ex. Mt. St. Helens and Nevado del Ruiz

volcano-related tsunamis

sea waves after collapse of volcanic cone

airplanes

What is volcanic ash a hazard to?

respiratory health

What are volcanic gases a hazard to?

effects of volcanic ash and gases on weather and climate

ash particles reflect solar energy back into space causing cooling

Crater-Lake Caldera

collapse of summit of large composite volcano following eruption, fill with rainwater

Yellowstone-type caldera

collapse of large area after discharge of large volumes of silica-rich pumice and ash, exhibit complex history

Basalt Plateau

fluid basaltic lava extruded from fissures blanket a large area, also called large igneous province, flood basalts appropriately describe these eruptions, ex. Colombia Plateau and Deccan Traps

Lava dome

small dome-shaped mass composed of rhyolitic lava, thick lava is squeezed out of a vent, produced dome shaped mass, collapse of a lava dome often produce powerful pyroclastic flows

Volcanic neck

remains of magma solidified in volcanic conduit, ex. Shiprock, New Mexico

Volcanic Pipe

conduit originated in mantle at depths exceeding 150km, very rare, ex. Kimberlite pipes

Divergent plate boundary

greatest volume of magma erupts along divergent boundaries, associated with seafloor spreading, vast outpouring of fluid, basaltic lavas

Convergent plate boundary

subduction zones, lithosphere descend into mantle, volcanic arcs, more violent than at divergent boundaries

Intraplate Volcanism

1000s of kilometers from plate boundaries, mantle plume ascends, surface manifestation of mantle plume is hot spot, superplumes are thought to be responsible for large basalt plateaus, ex. Hawaiian Islands, Yellowstone, Siberian Traps

hazard assessment

Why is volcanic monitoring critical?

GPS, InSAR

remote sensing devices

weathering

involves the physical breakdown and chemical alteration of rock at or near the Earth’s surface

mechanical weathering

disintegration, physical forces breaking rocks into smaller pieces

chemical weathering

decomposition, chemical transformation of rock into one or more new compounds

erosion

removal and transport of weathered rock by wind, water, or ice

surface area

mechanical weathering increases this which increases speed of weathering

frost wedging

water goes in cracks in rock and freezing enlarges the cracks

salt crystal growth

sea spray or salty groundwater penetrates crevices and pore spaces in rocks, as water evaporates, salt crystals form and enlarge the crevices

sheeting/unloading

large masses of igneous rock are exposed by erosion and concentric slabs break loose due to release of confining pressure

exfoliation dome

formed after continued weathering causes slabs to separate and peel off

joints

fractures formed by the contraction of magma during crystallization or produced by tectonic forces during mountain building

biological activity

plants grow into fractures in a rock and wedge the rock apart, burrowing animals breakdown rocks, enhancing physical and chemical weathering, decaying organisms also produce acids that contribute to chemical weathering

water

most important agent in chemical weathering

dissolution

process of dissolving into a homogenous solution, ex. Halite, small amount of acid in water increases corrosive force of water, causing dissolution, carbonic acid is created when carbon dioxide dissolves in raindrops, calcite is easily attacked by weakly acidic solutions, responsible for formation of limestone caverns

oxidation

process of iron-rich minerals rusting, oxygen combines with iron to form iron oxide, process is slow in dry environments, water increases speed of reaction, important in decomposing ferromagnesium minerals, like olivine, pyroxene, hornblende, and biotite, oxidation can only occur after iron had been freed from the silicate structure by hydrolysis

hydrolysis

reaction of any substance with water, hydrogen ion attacks and replaces another ion, silicates primarily decompose by hydrolysis, clay minerals are most abundant product of weathering, clay minerals are stable under surface conditions, acid greatly accelerates hydrolysis

spheroidal weathering

weathering attacks edges from two sides and corners from three sides, sharp edges gradually wear down and become rounded, eventually an angular block may evolve into a nearly spherical boulder

influences on rates of weathering

all of the chemical traits of rocks, including mineral composition and solubility, silicate materials weather in the same order as crystallization, temperature and precipitation are crucial, frequency of freeze-thaw, moisture available for dissolution, conditions favoring vegetation growth

differential weathering

rock masses do not weather uniformly

soil

the bridge between life and the inanimate world, portion of the regolith that supports the growth of plants

regolith

layer of rock and mineral fragments produced by weathering covering the earth’s land surface

humus

organic matter in soil that is produced from the decomposition of plants and animals

disintegrated rock and mineral matter and humus

about ½ of the total volume of good-quality surface soil is a mixture of ___

soil texture

refers to the proportions of different particle sizes, strongly influences the soil’s ability to transmit and retain air or water

platy, prismatic, blocky, and spheroidal

four basic soil structures

soil structure

influences how easily the soil can be cultivated, how susceptible it is to erosion, porosity, and permeability

loam

equal parts sand, silt, clay

parents material, climate, plants and animals, time, topography

five controls of soil formation

parent material

source of weathered materials that forms soil, influences soil by rate of weathering directly impacts rate of soil formation, chemical composition of parent material will affect soil fertility

residual soils

soils formed from bedrock

transported soils

soils develop from unconsolidated sediment

climate

most influential control of soil formation, key factors are temp and precipitation, determines degree and rate of mechanical and chemical weathering

plants, animals, microbes

influence the physical and chemical properties of soil , the primary source of organic matter in soil is plants, microorganisms play a role in the decay of plant and animal remains, end result is humus

bioturbation

earthworms and other burrowing animals mix mineral and organic portions of the soil

time

weathering over a short period of time forms thin soils that closely resemble the parent material, soils that have weathered for a long period of time are generally thick and do not resemble the parent material

horizons

soil is divided into layers called ___

soil profile

a vertical section through all the soil horizons

O soil horizon

organic matter, upper portion is primarily plan matter, water percolates downward carrying dissolved soluble inorganic soil into deeper zones, lower portion is made of partly decomposed organic matter, both portions are teeming with bacteria, fungi, algae, insects

A soil horizon

organic and mineral matter, high biological activity

topsoil

O and A horizons make up the ___

E horizon

little organic matter, light colored layer, eluviation, leaching

eluviation

washing out fine soil components to lower soil layers

leaching

soluble inorganic components washed to lower layers

B horizon

subsoil, zone of accumulation, material washed down from the E horizon accumulates in this layer

C horizon

partially altered parent material, parent material is difficult to identify in the O, A, E, and B horizons

impact of human activity on soils

agricultural productivity of soils can be improved through fertilization and irrigation, soils can be damaged or destroyed by careless activities, soils are crucial for providing food, fiber, and other basic materials, soils are one of the most abused resources

controlling soil erosion

when steep slopes are farmed, constructing terraces can help low runoff and decrease soil loss, strips of grass or cover crops parallel to slope also slow runoff and trap sediment, creating grassed drainage ways prevents the formation of gullies and traps soil

numerical dates

specify number of years that have passed since an event occurred

relative dates

place rocks in a sequence of formation

Principle of Superposition

Steno - 1669, in an undeformed sequence of sedimentary rocks, each bed is slightly older than the one above and younger than the one below