Natural Disasters Exam 2

what are the 3 types of magma?

basaltic (dark colored), andesitic (medium colored), rhyolitic (light colored)

which type of magma has the highest Silica content?

rhyolite

which type of magma is more viscous?

rhyolite

how do igneous rocks form?

molten rock cools and solidifies

what processes are responsible for changing a magma’s composition?

assimilation, magma mixing, crystallization and settling 

what is assimilation?

changing a magma’s composition by the incorporation of foreign matter (surrounding rock bodies)

what is magma mixing?

two bodies of magma intrude one another and produce a composition different from either original 

what is crystallization and settling?

as magma cools it crystallizes and forms solid rock

what are volatiles?

compounds that evaporate readily at normal temperatures and pressures (ex: water)

what are characteristics of basaltic magma?

• form by melting of asthenosphere

• most common magma type

• low silica content (45-55%)

• mafic composition 

• lithifies into basalt

• dark in color

what are characterisitcs of andesitic magma?

• intermediate composition

• 55-65% silica content

• lithifies into andesite

what are characteristics of rhyolitic magma?

• felsic composition

• >65% silica content

• lithifies into rhyolite

• light in color

what factors determine the violence of a volcanic eruption?

composition of magma, temperature of magma, dissolved gases in magma

what is viscosity?

measure of a material’s resistance to flow

what is the relationship between viscosity and temperature?

hotter magmas are less viscous (ex: honey)

what is the relationship between viscosity and dissolved gases?

gases expand within magma as it nears the Earth’s surface due to decreasing pressure (ex: bubbles in soda)

what is the relationship between viscosity and silica content?

greater amounts of silica make it more difficult for magma to flow

what are characteristics of a stratovolcano?

• large, classic shaped 

• composed of interbedded lava flows and layers of pyroclastic debris

• ex: volcanoes at Cascade Range, Ring of Fire

• high viscosity and high volatility

what are characteristics of a lava dome volcano?

• often form in vent of stratovolcano after an explosion

• much smaller than a stratovolcano

• high viscosity magma (forms plug that traps gas)

• form as a separate isolated volcano

what are characteristics of a shield volcano?

• broad, slightly dome shaped

• composed of mostly basaltic lava

• largest volcanoes in the world

• produced by mild eruptions of large volumes of lava that flows great distances

• common in Hawaii, Iceland, African Rift

what are characterisitcs of a cinder cone volcano?

• built from ejected lava fragments near vent

• associated with basaltic eruptions (low to intermediate explosivity)

• steep slope angle

• rather small size

• frequently occur in groups

where are most volcanoes located?

within or near ocean basins, subduction zones

what are primary effects of volcanoes?

lava flows, ash fall, pyroclastic flows, lateral blasts, release of volcanic gases

what are secondary effects of volcanoes?

debris flows, mudflows, landslides, floods, fires, tsunamis

how many volcanoes erupt each year worldwide?

50 to 60

how many people live close to volcanoes?

500 million (Japan, Mexico, Phillipines, Indonesia, US)

what processes are part of the hydrologic cycle?

precipitation, evaporation, infiltration, runoff, transpiration

what are streams?

any body of water that flows through a channel, small rivers

what is the drainage basin?

the land area that contributes water to a stream

what is the equation for stream discharge?

discharge = velocity x cross-sectional area

what is abrasion?

bedrock channels and individual sediment grains are bombarded by particles carried by the stream which erodes the bedrock and rounds the particles

what is limestone made of?

calcite

what are the two types of stream valleys?

narrow and wide

what are characteristics of narrow stream valleys?

• V-shaped

• downcutting towards base level

• rapids and waterfalls

what are characteristics of wide stream valleys?

• stream is near base level

• downward erosion is less dominant

• stream energy is directed from side to side forming a floodplain

what are floodplains?

flat areas found on either side of a river channel, periodically occupied by the stream during flooding 

what is zone 1 of a river system?

zone of production (fast velocity, downcutting, erosion)

what is zone 2 of a river system?

zone of transport (braided or meandering)

what is zone 3 of a river system?

zone of deposition (alluvial fan, lake, delta)

what is mass wasting?

the downslope movement of rock and soil under the direct influence of gravity

what does the combo of mass wasting and running water produce?

stream valleys or canyons

what are triggers for a landslide?

saturation of material with water, oversteepening of slopes, removal of anchoring vegetation, ground vibrations from earthquakes

what is the angle of repose?

stable slope angle

what are the 4 variables that mass wasting events are classified into?

1. type of material (debris, mud, earth, rock)

2. mechanism of movement (slide, flow, fall)

3. amount of water present

4. rate of movement 

what is a creep?

gradual movement of soil downhill

what do driving forces do?

move materials downslope (weight of slope material)

what do resisting forces do?

oppose downslope movement (strength of material)

how is slope stability measured?

ratio of resisting forces to driving forces (stable when >1, unstable when <1)

what are ways to increase slope stability?

grading (material from upper slope moved to base), adding slope supports

what is soil?

solid earth material that has been altered by physical, chemical, and organic processes such that it supports life

what factors control soil formation?

parent material, time, climate, plants and animals, slope

what type of magma erupts from Hawaiian volcanoes?

basaltic

__ magma is the most viscous (sticky); therefore, it
produces ________ eruptions

rhyolitic; violent

Which type of magma has the highest silica content: basaltic, andesitic, rhyolitic?

rhyolitic

Name three geologic events associated with the eruption of Mount St. Helens

earthquake triggered a landslide, pyroclastic flow, lahar

how does a caldera form?

collapse of the volcano into the magma chamber after eruption

It would be unwise to build your house along the _______ of a stream because erosion is the dominant force there?

cut bank

What does the dissolved load in streams consist of?

dissolved ions (minerals)

What happens to the discharge of the Colorado as it reaches its mouth (Gulf of California)? Why?

Discharge decreases to near zero (no flow) because of all the big cities that use Colorado River water (Las Vegas, L.A.)

how does urbanization affect lag time?

Shortens the lag time (time between rainfall and flooding)

A river system consists of three zones. Which of the
following is characteristic of Zone 3?
•A) Broad floodplain
•B) Flash flooding
•C) Formation of a delta
•D) Erosion

C) formation of a delta

what 2 horizons make up the topsoil?

O and A

It takes 500 years for 2 _____ of soil to form. From this we see that time greatly affects soil development
•A) meters
•B) inches
•C) feet
•D) kilometers

B) inches

name 2 features associated with Karst topography

sink holes, caves

How have humans contributed to subsidence
along the Mississippi Delta? List three ways

• Restricting sedimentation by building dams and levees

• Withdrawal of oil and groundwater

• Canal building which allows salt water to invade and kill plants

A soil _________ is an arrangement of soils from youngest to oldest based on their relative development

chronosequence

what happens when driving forces overcome resisting forces?

landslide

Wildfires are a frequent occurrence in California. Which
mass wasting process typically follows the first rainstorm
after a fire?

debris flow

what causes soil to creep?

Expansion and contraction of the ground due to freeze/thaw cycles, causing soil particles to move downslope

Rocks do not weather uniformly which causes overhanging ledges of resistant rocks over eroded ones. What type of mass wasting event would this likely cause?

rock fall

List some factors responsible for causing the large Gros
Ventre landslide outside of Jackson, WY

Rain and snowmelt saturated a sandstone layer that rested on top of an impermeable (and slick when wet) layer of shale (clay)

When did Lake Bonneville reach its highest elevation?

17,000 years ago

What caused the lake level to drop precipitously over the
course of a few weeks/months from its highest level?

A catastrophic flood at Red Rock Pass in southern Idaho

What type of volcano typically occurs in clusters and has a life span of several years

cinder cone

What type of mass wasting event occurs as blocks of rock slide down a slope?

rock slide

what forms when a river abandons its meander?

oxbow lake

what is the difference between a rock slide, fall, and flow?

slide: downslope movement of a coherent mass

fall: free fall of rock/debris from a steep slope or cliff, material detaches and falls

flow: material moves downhill like a viscous fluid, often involved water saturated material