ACTUAL GEOLOGY EXAM 2

• Three main processes that generate magma (why does it work and think of relationship of the phase diagram), also where this happens tectonically

• decrease pressure

  • as pressure decreases, melting point of rocks also decrease 

  • where this happens: mid-ocean ridges, rifts

  • the mantle is typically solid at high pressures, but when it upwells due to convection, it experiences a drop in pressure. if this drop occurs faster than heat can escape, this leads to magma generation

• increase heat

  • adding heat can raise temperature of rocks beyond melting point, generating magma

  • where this happens: hotspots

  • heat increase shifts temperature of rock towards the melting line, allowing for partial or complete melting

• addition of water

  • water helps break apart Si-O bonds, lowering the energy needed to melt

  • where this happens: subduction zones

  • water disrupts crystal structure of minerals, shifts solidus to lower temperatures

• Silicate magma and role of polymerization

• magma primarily consists of silicate minerals

• more silica → more viscous

• high polymerization → more silica

• low polymerization → silica-poor, mafic, low-viscosity 

• more fluid lava flows and less explosive eruptions

• Bowen’s Reaction Series – what does it look like, what does it tell, overall importance

• illustrates the crystallization sequence of minerals from a cooling silicate magma

• high temperatures → olivine first mineral to form from silicate melts before pyroxene crystallization started and olivine growth slowed and stopped

• At the same time olivine and pyroxene grew, a calcium-rich plagioclase feldspar crystallized. as temperature dropped, the composition of the plagioclase became more Na-rich

• after a period of time, pyroxene growth slowed and stopped while hornblende amphibole started crystallizing, and so forth

• when temperature drops low enough, K-feldspar, muscovite, and quartz may form

• Viscosity and factors affecting it

• silica content → controls most of the physicochemical properties like density, viscosity, etc. 

• composition of the melt 

• higher polymerization = higher viscosity 

• temperature decreases, viscosity increases

• concentrations of volatiles are the most important factor (other than magma composition) for controlling magmatic viscosity

• Different shapes of plutonic intrusions

• dikes, dike swarms, radial dike swarms, sills, stocks, batholiths

• shield volcano characteristics (size, rock composition, slope, vent(s), magma comp) 

• size ranges from a few km to hundreds of km

• mostly basaltic

• low slope <10°

• usually one primary central vent but other flank eruptions are common

• magma is “runny” and will flow for long distances

• what are shield volcanoes a result of? 

• low viscosity magma (runny)

• low volatile content magma → causes things to explode

• good example of a shield volcano: 

1. hotspot volcanoes

• characteristics of stratovolcanoes / composite volcanoes: (size, rock composition, slope, vent(s)

• size up to a few kms across

• mostly andesitic but span a wide range of compositions

• steep slope (15-26°) 

• multiple vents

• viscosity, volatile, other events that are involved in strato / composite volcanoes: 

• high viscosity magma

• medium-high volatile content

• composed of lava flows, pyroclastic deposits, and plutonic bodies

• classic example of caldera on stratovolcano: 

1. Crater Lake in Oregon

• what are cinder cones? 

• collection of ash, lapilli, and blocks from a central vent during weakly explosive eruptions

• characteristics of cinder cones: (size, rock composition, slope, shape, vent(s))

• size up to a few hundred meters tall and a couple of km wide

• mostly basaltic

• slope is usually 33°, the angle of repose, which is the angle substance will form as it piles up and gravity tears down to a certain angle. scoria (vesicular volcanic rock) angle of repose is 33°

• central bowl crater that flattens over time

• one central vent

• cinder cones often form in groups

• what is a caldera volcano? 

• bowl-like structure

• major collapse features that form as a result of magma drainage

• geologic possibilities of calderas:

• in basaltic shields, the caldera may fill to form a lava lake 

• in more silica volcanoes the caldera collapse can lead to catastrophic eruption

• what events do caldera eruptions typically involve? 

• pyroclastic flows

• pyroclastic falls

•  two geographic places there are calderas

• Nyiragongo, Zaire

• Mauna Loa, HI

• characteristics of caldera forming / Ultraplinian eruptions: (explosivity, composition, location)

• extreme explosivity

• mostly rhyolitic 

• stratovolcanoes ONLY

• what do Ultraplinian eruptions form? 

calderas

• two major areas in the US that have experienced fairly recent caldera activity: 

• Yellowstone

  • Long Valley, CA

• two caldera-forming events, what do they compare to? 

• in the Campi Flegrei area in Naples, Italy

• close to the scale of Long Valley Caldera 39,000 years ago and 12,000 years ago

• describe pahoehoe flows: (viscosity, flow, volatile content)

• lava flow that flows because it has very low viscosity

• smooth flow

• low volatile content → no gases

• describe A’a flows:

• lava flow that forms at top and sometimes bottom of flow → oftentimes a “crust”

• material is solidifying and tumbling

• describe basaltic lava flows: 

• can make thin and extremely extensive flows (can flow hundreds of km)

• why are basaltic lava flows important? 

there is a bunch of carbon dioxide in these areas, which can be released into the atmosphere and impact climate

• describe blocky lava flows:

• forms from higher viscosity and thicker flows

• characterized by irregular but smoother surfaces and decimeter to meter size blocks

• describe lava tubes (where, flow, heat)

• natural tunnels where molten lava flows beneath the surface 

• form that allow lava to flow rapidly without using heat

• doesn’t solidify, stays at higher heat

• Six Eruptive Styles – products, differences and where do they occur?

• Icelandic / fissure → mid-ocean ridges and rift zones

• Hawaiian → hot spots and shield volcanoes

• Stombolian → cinder cone volcanoes and stratovolcanoes

• Vulcanian → stratovolcanoes

• Plinian → subduction zone stratovolcanoes

• Ultraplinian → stratovolcanoes ONLY

• Origins of calderas and their effects

• formed by volcanic collapses, major eruptions, or magma drainage

• super powerful; climate change, create volcanic lakes, create lava domes

• aside from lava flows and pyroclastic material, what other problems do volcanoes cause? 

• lahars

• landslides

• poisonous gas clouds

• climate change

• effects of lahars

• killed almost 25,000 people in 1985 in Columbia by a small eruption 

• can occur from very small eruption, and  also be caused by lots of precipitation weathering volcanic material

• the Cascades are also worrisome

• what occurred around Long Valley (Mammoth Mt.)?

• poisonous gas flow that caused die-offs

• what happened in Lake Nyos? 

• turnover of CO₂ that killed 1700 people

• danger of vog

• high acidity

• what is laze

• HCl vapor and micro-shards resulting from interaction of lava and seawater

• causes health issues

• eruption of Laki caused: 

• released lots of sulfur dioxide and hydrogen fluoride

• killed lots of animals, crops, and people in Iceland, as well as in Europe and probably other places too

• what did the Eruption of Tambora in 1815 cause? 

• climate change

• caused the “Year Without a Summer” 

• massive crop failures and famine

• what kind of eruptions cause climate change and how?

• major plinian eruptions

• cause acid rain in troposphere

• increase amount of solar radiation that goes back to space (albedo) of earth’s stratosphere

• what did Mt. Pinatubo in the Philippines produce? 

• sulfur dioxide cloud that increased acid rain in the tropics

• long-term effects of aerosols (particles in atmosphere) decreased temperatures for a little over a year

• talk about supervolcano eruption of Toba (Lake) 75,000 years ago!

• may be why modern humans exist

• The Toba Tuff is found in meter size deposits in southeast Asia (meters of volcanic deposit)

• different climate models suggest massive global temperature drops

• types of physical weathering: 

• abrasion 

• ice wedging

• temperature changes → causes columnar joints

• pressure → causes joints and exfoliation joints

• root wedging

• burrowing creatures

• what does physical weathering do? 

• break a rock down into smaller pieces of the same rock, creates more surface area on a rock sample 

• what does chemical weathering do? 

• breaks down a rock’s minerals into their basic components or changes a rock’s minerals into new minerals that are more stable at Earth’s surface

• types of chemical weathering: 

• dissolution → minerals break down to ions in solution

• hydrolysis → anhydrous minerals are changed into hydrous minerals (H₂O or OH^- bearing)

• oxidation → minerals add oxygen through interaction with air

• Relevance of Bowen’s Reaction Series in weathering?

• everything wants to be at its most stable, so the new minerals from old rocks will slowly change to new minerals, typically quartz, clay minerals, and oxides / hydroxides. 

• Bowen’s Reaction Series in weathering predicts how resistant minerals are to weathering at Earth’s surface

  • minerals that crystallize first, at high temperatures, like olivine and pyroxene, are least stable at the surface, and are more susceptible to breakdown when exposed to water, oxygen, and cooler temperatures. Minerals that crystallize last, like quartz, muscovite, and K-spar, are more stable and resistant to weathering

• what factors control how and how quickly a rock weathers? 

• time

• mineralogy

• solubility

• climate / temperature

• precipitation

• topography

• soil

• Agents of erosion & energy

• wind, water, ice

• wind has not a lot of energy

• water can carry any size

• ice sheets has most energy, can literally carry anything and keep it in there as long as its frozen

• clastic sedimentary rocks: 

• deposition of pieces of rocks or minerals

• (bio)chemical sedimentary rocks: 

• deposition of ions that come out of solution either by biological or physicochemical processes

• What is the CCD and why is it important?

• calcium carbonate compensation depth 

• depth at which calcium carbonate is no longer stable but will instead break down into dissolved CO₂

• determines marine sediment composition, above CCD you find shells, carbonate sediments, certain organisms, etc.

• plays a role in the marine carbon cycle, affecting how much carbon is locked away in sediments vs. returned to the water / atmosphere

11 main depositional environments

1. continental: rivers (alluvial), beaches, deltas, tidal flats, lakes, deserts, glaciers

2. oceanic: continental shelf, reefs, continental slope, deep sea

• when ocean water is trapped in enclosed basins and evaporates, what happens? 

• leaves behind minerals formed from the major ions of seawater, resulting in the deposition of evaporite minerals such as halite and gypsum

• what is evaporite crystallization?

• sequential precipitation of evaporite minerals as seawater evaporates

• follows a predictable order based on the solubility of different ions

• geographical example of continental evaporite site: 

• Aral Sea in Central Asia

• marine vs. continental evaporite sites: 

• marine → formed from seawater evaporation in restricted basins, ex. Persian Gulf. seawater flows in but can’t flow out easily

• continental → formed from evaporation of inland water bodies like lakes, occurs at arid or semi-arid regions, ex. Aral Sea in Central Asia

• examples of evaporite deposits (minerals): 

• rock salts

• rock gypsum

• carbonates

• Formation of coal – how, when, and where

• when plant lignin is accumulated in an environment that does not allow significant decomposition to take place

• environments that are low in oxygen, like swamps and estuaries

• when were Eastern coal deposits formed? 

• Carboniferous period (Pennsylvanian and Mississippian)

• when were Western coal deposits formed? 

• Cretaceous period 

• Ranks and Grade of coal

ranks → peat, lignite, sub-bituminous, bituminous, anthracite, and potentially to graphite

• grades → low grade are lower energy and include peat, lignite, and sub-bituminous; high grade include bituminous and anthracite

• increasing coal grade does what to the volatility? 

decreases

• Where coal distributed and how evenly

• major deposits are found in North America, Russia, China, and India

• Environmental Problems with coal

• coal mining leads to acid mine drainage

• burning coal contains toxic heavy metals, airborne particles that cause health issues, and improper disposal = pollution

• what are oil and natural gas? 

• hydrocarbons made up of carbon, hydrogen, and oxygen

• most oil is formed by:

• death and accumulation of phytoplankton on the seafloor where sediments accumulate rapidly and little biological activity or oxidation can occur

• where must oil / natural gas come from? 

• a source rock that is organic rich

• process of producing oil: 

• entering the heating window (50-100℃)

• organic molecules break down to form large heavy hydrocarbons or heavy oils

• large molecules break down under additional heating by the process of cracking to smaller, lighter molecules like methane

• what is a trap in oil formation? 

• geological structure that prevents oil and gas from escaping and allows them to accumulate in one place

• where are most oil fields primarily found? 

recently active convergent plate boundaries because they have high sedimentation rates and are more likely to have low oxygen conditions

middle East, North America, Russia

• what continent has never had oil or natural gas? 

• Africa → doesn’t have the proper geology

• Four types of oil traps:

• anticline, fault, stratigraphic, salt dome

• what are sedimentary rocks composed of? 

• grains (sediments / clasts), cement and / or matrix (fine grained material that fills space between larger grains), and porosity

• what does cementation depend on and what kinds are there? 

• largely driven by what chemical constituents are around

• silica (quartz or amorphous), calcite, Fe oxides / hydroxides, clay minerals

• what is porosity? 

• space with no mineral matter, commonly filled with water

• what does porosity depend on? 

• amount of ductile mineral (clay matrix, lithic non-quartz grains) during compaction

• what is the most common type of sedimentary rock and why? 

• shales

• abundance of shale, siltstone, and mudstone accounts for 75% of sedimentary rocks

• **main reason → lots of different depositional environments 

• easily transported because of size, low energy → less likely to be eroded during formation

• what is the process of lithification or diagenesis and what is it driven by? 

• process of turning sediments into sedimentary rock

• driven by burial, compaction, and cementation

• what is Walther’s Law (1894)? give an example

• states that “facies sequences observed vertically are also found laterally” 

• means that vertical sequences will be the same as those elsewhere horizontally but at different heights

  • for example, the beach that is located near Stockton was somewhere else during the last ice age, and in another hundred years, Stockton will be underwater. point is, sea level changes, which changes beach location – this is just an example

• what are transgression and regression cycles of sea level rise / fall? 

• describe changes in sea level relative to land and shifting distribution of marine and terrestrial environments

• what do transgression and regression cycles of sea level rise / fall do sedimentary wise? 

• when sea level rises, shoreline moves inward, deeper water sediments deposit over shallow water sediments

• when sea level falls, shallower water sediments are deposited over deeper water sediments

• what are turbidites? 

• turbidity currents

• density driven currents as slope changes in a body of water that are water containing huge amounts of sediments 

• VERY VERY POWERFUL EVENTS

• what can turbidites be triggered by? 

• earthquakes and tsunamis

• slope failure

• storms

• volcanic eruptions

• what do turbidites typically produce? 

• special characteristic graded bedding called a Bouma sequence

• this represents the layered structure of sediments deposited by the currents

• what are mudcracks formed from? 

• cracks that form in sediments when mud dries out and contracts

• what environments are mudcracks found in? 

• shallow lakes, wetlands

• what do mudcracks tell us about the environment they are in and the climate? 

• suggest the environment went through periods of wetting and drying, indicating evaporation or seasonal fluctuations

• suggest air or semi-arid climate conditions

• what are ripple marks? 

• small, wave-like ridges formed by the movement of water over sand or silt

• what do ripple marks tell us?

• steeper side indicates the direction of flow

• small, symmetrical ripple marks typically form in low energy environments, larger, asymmetrical form in higher energy environments

• what environments do ripple marks form in? 

shallow marine, lake, or river environments, often in tidal or current-dominated settings

• what are dunes? 

• big piles of sand formed by wind in desert or coastal environmentsbig piles of sand formed by wind in desert or coastal environments

• what do dunes tell us? 

• indicate a significant influence of wind 

• indicate arid conditions

• direction of dune migration can help determine prevailing wind

• what is cross-bedding? 

layers of sediments that are at an angle to the horizontal bedding plane, formed by the migration of dunes

• where is cross-bedding found? 

• dunes

• common in high-energy environments

• what does cross-bedding tell us? 

• angle of cross-beds tell us direction of wind that formed them

·       Soil Horizons – what is where and what goes on there; subscript letters, what do they tell us

• O - organic dominated

• A - dark layer of minerals + organics that are starting to leach

• E - light colored leaching layer; resistant mineral rich

• B - zone of accumulation, layer enriched in dissolved components

• C - partially altered rock material 

• R - unaltered bedrock

• subscript letters are added to describe the characteristics of the layers

• the thickness of composition of the horizons defines differences between the twelve orders of soil taxonomy

·       Processes – Translocation, leaching, accumulation, and transformation

• translocation: stuff moving

• transformation: stuff changing, chemical weathering **

• accumulation: (illuviation), dissolved ions accumulating them in an area

• leaching: (eluviation), downward motion of dissolved ions

·       Factors controlling soil formation

1. bedrock composition (parent)

2. climate 

3. organisms - what organisms are dying and contribution to formation

4. time

5. topography - in the mountains, not a lot of soil present

·       12 Taxonomic soil types – good soils from bad soils and generalities of them

1. Good: Alfisols, Andisols, Inceptisols, Mollisols, Vertisols (with management)

Bad: Aridisols (without irrigation), Gelisols, Oxisols, Spodosols, Ultisols (unless managed).

Nutrients

• nitrogen, phosphorus, potassium

·       Soil Issues: erosion, desertification, pollution

• erosion causes the fertile top layer of soil to be the first to go, this is the nutrient-rich layer

• eroded soil can wash into rivers and lakes, contributing to water pollution