Geology Exam 2

Tectonic Activity and Volcanoes, Earth and Time

Pyroclastic Debris

block, bombs, lapilli (tiny rock particles), ash

Pyroclastic Flows

mixing of pyroclastic debris and water (dangerous)

Volcanic Gases

most magma contains dissolved gases which come out of the solution when the magma reaches the surface

Two Results of Volcanic Gases

gas bubbles leave magma and create steam OR gas bubbles don’t leave magma (vesticles, scoria, pumice)

Two Reasons volcanic gas comes out as magma

Release of Pressure and Mineral Crystallization

Mafic Magma

low viscosity, flowy/thin lava flow

Intermediate Magma

medium viscosity, thick but spreadable flow

Felsic Magma

high viscosity, thick and pileup flow

Cinder Cone Volcano

small in size, made up of primarily solid ejecta

Shield Volcano

very wide, primarily basaltic flow (low viscosity and flowy therefore gentle slopes)

Composite Volcano

very wide and tall, different types of material (layers of liquid lava and solid tephra), felsic (clumps lava in layers, forming steep slopes)

Caldera

magma provides stability for the volcanic structure and therefore may collapse when it is gone

Effusive

small, explosive eruptions (lava can erupt out of a conduit or a fissure)

Explosive

immense eruptions

Hawaiian

predominantly effusive lava

Strombolian

periodically erupts lava, lapilli, and ash

Vulcanian

erupts lava, lapilli, and tall plumes of ash

Plinean

huge explosion that sends a convective cloud to high altitudes, produces pyroclastic flows, and may destroy the volcanic edifice

Ocean-Continent Convergent Boundary

volatiles to magma, intermediate to felsic volcanism

Ocean-Ocean Convergent Boundary

volatiles to magma, mafic to intermediate volcanism

Mid-Ocean-Ridge Divergent Boundary

decompression melting to magma, mafic volcanism

Rift Divergent Boundary

decompression melting to magma, mafic to felsic volcanism

Hot Spot

heat to magma, mafic to intermediate volcanism

Volcanic Hazards

lava flow and ash fall

Distance of Hazards (least to most)

lava flow, mud flow, pyroclastic flow, ash fall

Predicting Volcanic Eruptions

tracking gas composition and earthquakes, changes in volcano shape, heat, or temperature

Areas Earthquakes Occur

along mid ocean ridges (divergent) and near costal zones (convergent)

Causes of earthquakes

fault generation and stick-slip behavior

Fault Generation

solid piece of rock fractures from elastic bending, slip vibrates and vibrational energy causes the earthquake

Stick-slip Behavior

rock faces “slip” across each other and angular rock “teeth” get caught and stuck, friction makes them want to move, the stored energy gets too great and slips, releasing the energy and causing the earthquake

Focus

where the earthquake physically happens along the fault

Epicenter

‘where” the earthquake happens on the surface

Primary (P) Waves

compressional, travel fastest, vibrate directly parallel to the direction of wave movement

Secondary (S) Waves

shear waves, second fastest, vibrational direction is perpendicular to direction of wave movement

Love (L) Waves

slowest, travel back and forth like a snake

Rayleigh (R) Waves

slowest, go up and down through circular paths

Seismometers

can detect different seismic wave motions depending on their orientation

Fault

a fracture that separates 2 blocks of rock and along which shifting occurs

Dip-slip Faults

movement occurs along the dip of the fault with a component of vertical offset

Normal Fault

head wall down and foot wall up

Reverse Fault

head wall up and foot wall down

Strike-slip Fault

slip is along strike only (meaning only horizontal movement) with no vertical offsetW

Strike-slip faults occur at…

transformation boundaries

Normal faults occur at…

rifting zones and divergent boundaries (tensional forces)

Reverse faults occur at…

convergent boundaries (compressional forces)

Thrust Fault

type of reverse fault with lower angle where head wall is thrust on top of foot wall

Continent-Ocean Thrust Fault

the continental plate is thrust upon the ocean plate with some continental material, forming thrust and reverse faults

Continent-Continent Thrust Fault

the compressing continental plates form thrust and reverse faults

Steps to make a fossil

1. Creature dies

2. Hard parts remain

3. Bones get rapidly buried

4. Thick sequence of sediments accumulate over bones

5. Bones fossilize

6. Erosion occurs, exposing bones

Body Fossils

derived by fossilization of the body, or part of the body, of an organism

Body Fossils ex.

Frozen / dried fossils, fossils preserved in tar/amber, preserved hard parts, molds and casts, carbonized impressions of bodies, permineralized fossils

Trace Fossils

fossilized features formed from the action of an organism

Trace Fossils ex.

footprints, burrows, feeding traces, coprolites

Chemical Fossils

invisible fossils consisting of distinct chemicals or isotope ratios that form during the life activity of organisms (things organisms do that leaves a chemical trace)

Chemical Fossils ex.

Biomarkers (oil), C12 (evidence of photosynthetic organisms)

Sedimentation Rate

how fast sediments pile up to bury the organism

Fast sedimentation environments

desert, wind, tidal zone, mountain stream, floods, mudslides, volcanic events/ash burial

Low Energy Depositional Environment

keeps fossils in place but needs other processes to preserve

High Energy Depositional Environment

chaotic movement knocks things around, unable to preserve

Presence of Hard Parts

only hard parts (bones, shells) are generally fossilized with few rare exceptions 

Low Oxygen environment

nothing to decay or take away fossils

High Oxygen environment

lots of creatures to scavenge, likely to decay

Elements of Fossil preservation

Sedimentation rate, energy of the depositional environment, presence of hard parts, oxygen context of the depositional environment

Main Causes of Extinction

global climate change, tectonic activity, volcanoes, appears of new competitors, large asteroid/comet impact

Global Climate Change

species are adapted to a certain climate and when it changes they can go extinct

Tectonic Activity

tectonic plates shift around to regions where species cannot adapt

Volcanoes

giant volcanic eruptions put large volumes of ash and gasses into the atmosphere, changing the climate

Appearance of New Competitors

when a new competitor appears, it can outcompete and cause species to go extinct

Large Asteroid / Comet Impact

large enough impact occurs, debris go into the atmosphere, causing global cooling because the debris cloud blocks the sun

Relative Age

older or younger (order of events)

Absolute / numerical age

how many years ago (specific number / year)

Uniformitarianism

geologic processes that are currently happening have also happened in the past

Original Horizontality

through deposition, sediments accumulate first in horizontal sheets and stack on top of one another

Superposition

in a sequence of stacked rocks older rocks are near the bottom and youngest are near the top

Lateral Continuation

if there was some erosion, we can interpret the same sequence of oldest to youngest rock layers in other areas

Cross Cutting Relations

rocks that cut across other layers are interpreted as younger than the rocks they cut across

Inclusions

if pieces of a rock are embedded in another rock, that means the included rock is older than the rock it is embedded in

Baked Contacts

hot magma and lava intrude into rock layers and back the surrounding rocks they encounter

Fossil Succession

if known creatures are found as fossils the sequence of events can be determined from the time period they were alive

Unconformities

represent time intervals of non deposition and possibly erosion

Angular unconformity

occurs when something that has been deformed gets weathered and eroded, erosion happens on rocks that are at an angle

Nonconformity

occurs when sedimentary rocks overlie older intrusive igneous and/or metamorphic rocks, creating a large gap of missing geologic time

Disconformity

occurs when sedimentary rocks overlie older sedimentary rocks so it looks like a normal sequence but there is a gap of missing geologic time that can only be distinguished by using fossils

Radiogenic isotopic dating

Isotopic crystal clock stops ticking once the mineral has cooled below its closure temperature

Closure temperature

the temperature below which the isotopes in the mineral will stop decaying, “freezing” the mineral in time

Formation

interval of strata composed of a specific rock type or group of rock types that together can be traced over a broad region, representing the products of deposition during a definable interval of time

Geologic Contact

boundary surface between two formations

Stratigraphic Column

records sequence of rocks deposited or geologic events over time

Lithologic Correlation

similarities in rock type

Fossil Correlation

comparing fossil assemblages and matching them in strata