test 2 Flashcards
how many volcanos erupt a year
50-60
how people live in the vicinity of volcanos and what are the locations
500 million ppl
Japan, Mexico, philippines, indonesia, western north america
Is the distribution of volcanos random or not random?
Not
Occur in well defined zones or belts
2/3 of all active volcanos on land are located along _____
the ring of fire
tectonic setting determines:
The type of volcano
-mid ocean ridges, subduction zones, and hot spots
magma
molten rock below earth surface
becomes lava when reaches surface
viscosity of magma is controlled by
composition, mainly through silica content
silica affects ___
viscosity
how does silica rich magma flow ?
not easily
what does viscosity effect?
the flow of lava, the shape of the resulting volcano
high silica content
70-75%
High viscocity
intermediate silica content
60 - 65 %
intermediate viscosity
low silica content
50-55%
low V
limited silica content
below 40%
very low V
Lava Flows: Pahoehoe
Average flow rates - 30 km/h
Most flows travel between 10 and 50 km from the source
Kilimanjaro hasnt erupted in how many years?
2.5 billion
What are the shape and eruptive style of a volcano related to?
The chemistry and viscosity of their magmas
Types of Volcanos: Stravolocano / composite cone
Composition : andensite
Volatile Content: high
Shape: coned, steep sides, built of lava flows, and protoclastic cones
ex: mount Shasta California, mount helens, Washington
Types of Volcanos: Lava Dome
Comp: andesite to rhyolite
Volatile Content: low to moderate
Shape: dome shaped, steep sides
Eruption Type: effusive w/ lava piling up near the vent, can be explosive
ex: mount lassen, California
types of volcano: shield
Comp: basalt
V.C: low
Shape: gentle arch, shield shape, shallow slopes, built up of mainly lava flows
eruption type: traveling lava flows
Ex. Mount loa - hawaii
Types of Volcanos: Cinder Cone
Comp: basalt
V.C: low to moderate
shape: steep sides, coned, summit crater
Eruption type: mostly tephra ejection (nut to fist sized) lava flows
ex. SP Crater, Arizona
Types of Volcanos: continental calderas
Comp - rhyolite
VC: high
Shape: broad uplift w/ large summit depression
ET: tephra
ex: Yellowstone caldera , mount Manama
pyroclasts
magma fragments that are explosively ejected by volcanos and are mostly solid
pyroclastic materials
Ash : less than 2 mm diameter
Lapili : 2-64 mm diameter
bombs: part molten, less than 64 mm d
blocks: solid, less than 64 mm d
volcanic gases
mostly water vapor
erupted sulfur can have significant effects on climate
erupted sulfur effects on climate leads to lesser amounts of ………
carbon dioxide
nitrogen
sulfure dioxide
hydrogen sulfide
caldera
- the summit of a volcano collapse into its magma chamber following voluminous eruptions
-can be 1000s of meters across and 100s of meters deep
-can host lakes or become sites for new volcanic activity
hot springs
-geothermal activity
-hot rocks heat groundwater discharged at surface
gysers
-groundwater builds, erupting steam at a surface
what are pyroclastic flows?
huge sheet like eruptions of pyroclastic materials
ice contact volcanos
volcanos that erupt beneath or against glaciers
when they erupt the heat from the lava can melt the surrounding ice causing unique volcanic features and hazards
primary effects of volcanos
lava flows, ash fall, volcanic bombs, pyroclastic flows and surges, lateral blasts, poisonous gases.
secondary effects of volcanos
lahars, debris avalanches, landslides, groundwater and surface contamination, floods, fires, tsunamis.
how can the size of an eruption be quantified ?
by using the volcanic explosivity index
volcanic hazards - lava flows
Occurs when magma reaches surface
-moves fast or slow depending on viscosity and temp
-high viscosity moves slower
ways to divert lava flows
Barriers
Hydraulic chilling
diversion walls
volcanic hazards - pyroclastic flows
Avalanches of hot rock, ash, volcanic rock fragments
-hot and race down at 400km/h
volcanic hazards - pyroclastic surges
Dense clouds of hot gases and rock debris produced by explosive interaction of water and magma
Volcanic hazards : lateral blasts/explosive eruptions
Rock frag, gas, ash, are blown from side of volcano
ex.mount st helens 1980
volcanic hazards: lahars
Large amounts of loose volcanic ash and other pyroclastic material becomes saturated with water and rapidly move down slope
Links between volcanos and other ND’s
fires
landslides
earthquakes
climate change
why do people live near volcanos
fertile soils
source of power (geothermal energy)
mineral resources
recreational oppurtunities
creation of new land
red river flood 1997 Winnipeg
heavy snow pack - warming weather and rain
covered 2560km 2 (southern Manitoba, parts of North Dakota)
3 ppl dead
815 mil in damage
hydrologic cycle
Streams and rivers are part of this cycle
Evaporation of water from earths surface
water returns to ocean underground or across the land
gradient
Slope of the land which the river flows
Steepest at high elevations
Levels off as river approaches its base
Shown on longitudinal profile
cross sectional profile
Steeper side and deeper valley near headwaters
Wide floodplain usually present at base level
Differences due to higher flow velocity at higher elevations
As longitudinal profiles gown down a river….
Discharge ___
river width _____
river velocity _____
sediment size ____
sediment amount ___ and river slope ______
Increases
Increases
stays the same or slightly increases
decreasees
increases and decreases
discharge
The water volume flowing through a cross section
drainage baisin
Land that slops towards the sea separated by topographic ridges
4 major drainage baisins
Atlantic basins
Hudson Bay
arctic baisin
pacific baisin
River model stages
Youthful
Mature
old age
Youthful river stage
V shaped
Upper parts where there is steeper topography and more precipitation
water velocity is fast, down cutting, and erosion occur
coarse material in river
river often flowing over rock
river dominates bbottom of valley
Meandering patterns
Channel bends called meanders that migrate back and forth across the floodplains
floodplains
area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.
River flow and sediment transport process
1 river flow
2 sediment transport
3 erosion and deposition
The wide, flat region adjacent to a river
Sediment frequently deposited in river bars or on floodplain
areas that are able to be flooded periodically by the rivers
broad valley bottom
sediment loss and depositional landforms
Where river loses its load
May have fans or deltas as depositional landforms
sediment can be swept away into lakes or seas
Total load consists of:
Bed load
suspension load
dissolved load
Materials that roll, slide, bounce along bottom
bed load
Slit and clay particles that are carried into the water
suspension load
Materials carried as a chemical solution
dissolved load
Magnitude and duration of a flood are determined by:
Amount and distribution of a precipitation in drainage basin
Rate at which the precipitation soaks into earth
how fast a surface runoff reaches river
amount of moisture in soil
primary effects of flooding
Drainage caused by currents, debris, sediment to farms, homes, buildings, roads, etc..
Erosion and deposition of sediment related to loss of soil and vegetation
Secondary effects of flooding
short term pollution of rivers
Hunger and disease
homelessness
Service functions : fertilize lands
Service functions : fertilize lands
Service functions : aquatic ecosystems
Flooding clears rivers of debris and sweep nutrients
Service functions: sediment supply
Periodically flooding builds up elevation
Dam construction : upstream
As water enters reservoir, it slows, deposits sediment, and forms a delta
Dam construction : downstream
As water leaves dam, it is devoid of sediment and can erode sediment to transport instead of depositing
Slopes of the stream will decrease until equilibrium is reached
Human interactions : urbanization
ncreases magnitude and frequency of floods
Urban areas have impervious and greater storm servers
Bridges block debris, creating dams
Urban runoff can be 5x more than pre-urban conditions
levees
Barriers to keep flood waters contained
Breaks cause higher energy flows
can produce bottlenecks in upstream areas
need to be maintained
channelization
Straightening, deepening, widening, cleaning, or lining existing stream channels
Have adverse affects on fish and wetland wildlife
can cause benefits to some urban and rural areas and improves navigation
Minimizing flood hazards - channelization
Create a natural channel by allowing the stream to meander and reconstruct variable water flow conditions by:
Clearing urban waste to allow free flow
Producing existing channel banks by not removing trees
planting additional trees or vegetation
adjustments - flood insurance
Maps of 100 yr floodplain where created to determine risk
New property owners are required to buy flood insurance
building codes limit new construction on floodplain
codes prohibit building on 20yr floodplain
flood proofing
Raise foundation of buildings above flood hazard level
Constructing flood walls or mounds
using waterproofing construction
installing improved drains and pumps
landslide
is slow or rapid nearly vertical downward
movement of Earth’s surface
karst
Landscape resulting from ,
dolostone, marble, gypsum or rock sal
Soil expansion and contraction
- Changes in water content of soil
- Freezing and thawing
- Not usually life threatening, but are some of the most
widespread and costly natural hazards.
sinkhole
A depression or hole in the ground caused by the collapse of a surface layer, which can range from a few meters to several hundred meters in diameter.
subsidence
the gradual settling or sudden sinking of the ground surface, which can also create depressions that may vary in size.
permafrost
Soil or underwater sediment that stays completely frozen for 2 years or more
refreezes in winter,
thaws in summer
- When thawed, it can
create land subsidence - Extensive thawing creates
uneven soil called thermokarst - Frost-susceptible sediments
expand when they freeze - Causes frost heaving
permanently frozen ground that remains frozen all year round, found mainly in very cold regions
Continuous
permafrost
ground that has patches of permanently frozen soil, but some areas thaw during the summer.
discontinous permafrost
when permafrost exists in small, isolated patches that are surrounded by thawed ground.
sporadic permafrost
Climate controls the amount and timing of …..
rainfall and
duration of freezing temperatures
Sinkholes are common in…
humid climates
Expansive soils are common in areas with…..
wet and dry
seasons.
Collapsible soils are found in….
arid and semi-arid climates
Areas with extensive, below-freezing temperatures can host…..
frost heaving
Effects of Subsidence and Soil Volume Change
Sinkhole formation
Damage highways,
homes, sewage facilities,
etc.
* Probably triggered by
fluctuations in water table
Effects of Subsidence and Soil Volume Change
Groundwater Use and
Contamination
Caves create direct
access between surface
and groundwater.
- This access can make
water vulnerable to
pollution, especially
during drought and when
sinkholes are used as
landfills.
Effects of Subsidence and Soil Volume Change
soil volume changes
Causes billions of dollars is
damage annually to
highways, buildings, and
structures.
- Swelling of expansive soils
and frost heaving - Damage caused by soil volume
change exceeds the cost of all
other natural hazards
combined.
Effects of Subsidence and Soil Volume Change
salt mining
- Coal mine structures have
collapsed. - Water is used to dissolve
and pump out salt, leaving
behind cavities. - Flooding in salt mines can
also cause sinkholes.
Best solution is to avoid
building in vulnerable areas
through:
- Geologic and soil mapping
- Surface features
- Subsurface surveys
Subsidence and Sediments
