Hazardous Earth Flashcards
What is a moho ?
mantle - crust boundary is marked by this
what two layers is the upper mantle made from ?
asthenosphere
lithosphere
what is the asthenosphere ?
layer that extends from 100km to 300 km solid but flows under a pressure
what is the lithsophere ?
lies immediately above the asthenosphere
rigid layer sandwiched between crust and astenosphere
what is the thickness of the crust ?
continental =
mean = 35km
min= <30 km
max = 70km
oceanic - 5-10km
what is the thickness of the mantle ?
to a depth of 2900km
what is the density of the crust ?
continental = 2.6-2.7
oceanic = 3.0
what is the density of the matle ?
3.3 @moho
5.6 @core
what is the mineral composition of continental crust ?
mainly granatic, silicon , aluminium
what is the mineral composition of the oceanuc crust ?
mainly basaltic, silicon and magenisum
what is the mineral composition of the mantle ?
rich in magnesium and iron
who invented the continental drift theory ?
Alfred Wegener
when did Alfred Wegener invent the continental drift theory ?
1912
what is the continental drift theory ?
carboniferous period, 250 million years ago, large single continent , pangaea existed
slowly broke apart into two land masses
moevemtn continued to the present day as the continents seperated and spread across globe.
why was wegener’s theory rejected ?
rejected by academic geologists who dismissed the evidence , preffering their own dominant ‘fixed earth’ paradigm
what is the geological evidence of the continental drift theory ?
fit of continents like S america and africa
evidence from about 290 million years ago of the effects of contemporaneous galciation in S Africa, Australia, S America, India and Antartica . Suggesting that these land masses were joined at this time, located close to south pole
- mountain chains and some rock sequences on either side of oceans show great similarity e.g. NE Canada and N Scotland
what is the biological evidence of continental drift theory ?
-similar fossil brachiopods (marine shellfish) found in Australian and Indian limestones
- similar fossil animals found in S America and Aystralia , especially marsupials
- fossil from rocks younger than the carboniferous period, in places such as Australia and Inidia, showingfewer similarities, suggesting that they followed different evolutionary patterns
what is another word for a divergent boundary ?
constructive
what is another name for a convergent boundary ?
destructive
where do divergent plate boundaries occur ?
locations where plates diverging (moving apart) are rising through the asthenosphere and forcing its way to the surface
what is especially notable at a mid ocean ridge ?
plumes of rising material
what is a mid ocean ridge ?
most spectacular relief feature on the planet but remain hidden at an average of 2.5km below ocean surface
very long chains of mountains - in places 3000m above the sea bed
added together these submarien mountain chains have a comibned length of 60,000 km
are mid ocean ridges contionuos or non-continuous ?
not continuous
how are frequent intervals of mid ocean ridges broken into segments ?
by transform faults
what is palaeomognatism ?
ancient record of changes in Earth’s polarity is known as this
echo sounders used to locate submariens for the first time, the existence of the Mid -atlantic ridge
what is sea floor spreading
moves material across the ocean floors as a ‘conveyor belt’ operating on each side of the mid -ocean ridge
what is the prediction of the ageof sea floor rocks ?
ocean - rocks would get older the further one was from the mid-ocean ridge
what was the actuality of the age of sea floor rocks ?
cores also sjwed that nowehere i the oceans was rock older than 200 million years, this confirmed that the ocean crust was constantly recycles over this period
what is a transform fault ?
displace mid ocean ridge laterally
- tens or hundreds of km
- as they slip - energy is released in form of earthquakes
- volcanoes = absent
why are volcanoes absent at mid ocean ridge ?
bocs conservative margin
what is the rate of spread of a fast spreading boundary ?
up to 16.5 cm/yr
what is the rate of spread of a medium spreading boundary type ?
5-10 cm per year
what is the rate of spread of slow spreading boundary type ?
2-3 cm per year
what type of landforms are there at a fast spreading boundary ?
broad and smooth mountain shains , no centra rift valleys
what type of landforms are there at medium spreading boundary ?
poorly defined central rift valleys , relatively smooth mountain shains
what type of landfroms are there at slow spreading boundary ?
steep slopes to mountains chains , clearly defined central rift valleys
give an example of a fast spreading boundary ?
east pacific rise (pacific and Nazca
what is an example of a medium spreading boundary ?
galapagos ridge (just south of the Nazca and Cocos plate boundary )
what is an example of a slow spreading boundary ?
mid - atlantic ridge (N AMerica and Eurasia and S America and African plates )
what is pillow lavas ?
magma erupting directly on to the sea bed is cooled rapidly , forming rounded mounds.
how is pillow lava formed ?
magma rises - pressure reduces - liquifies
how are underwater rift valleys formed along mid-ocean ridges ?
overlying rocks are forced upwards as the lithopshere is plaes under stress and eventually fractures
how was iceland created ?
north atlantic - extrusion of magma has been so great is has created the world’s largest volcanic island -
what are black smokers ?
superheated jets of water somethimes re-emerge on the ocean floor containing metal sulphides
what is good about black smokers ?
support unique and highly specialised organisms and ecosystems
what are rift zones ?
not confined to the ocean floor also occur on land and in part explain how continents can break up
what must be a thin consistency for rifting to occur ?
continentla curst
give an exmaple of rift stretching ?
from Red Sea northwards to Turkey
what is a graben ?
here , crust has been uplifted and stretched causing faulting and forming a sunken valley known as a graben
how was the red sea formed ?
rift widened, magma erupted at the surface and eventually the rift valley sunk below sea level
What is the lowest point of the Dead Sea ?
-400m which is the lowest point on the continental surface
what are the three types of convergent boundaries ?
oceanic continental
oceanic oceanic
continental continental
what happens at the oceanic - continental boundary ?
different densiities - when oceanic and continental converge the denser oceanic plate is forced under continental = SUBDUCTION
what does subduction cause ?
a deepening of the ocean at the plate boundary and forms an ocean trench
what are some features of an ocean trench ?
depths of 6000- 11,000 m
long
narrow
asymmetric
steepest side twoards continent
depressions
what is slab pull ?
oceanic crust descends into te asthenosphere , pulling the rest of the ocean plate with it in a process called slab pull
how is an ocean trench formed ?
leading edge of the overiridng plate is buckled
how are mountain chains formed ?
layers of sediment and sedimentary rock develops on oceanic plates adjacent to continents
As oceanic plate converges on continental plate, these sediments and rocks crumple, fold and are uplifted along the leading edge of the continental plate
ALSO - Cntinental crust is buckled and uplifted , and significant amounts of molten material are injected into it.
what is an example of mountain chains ?
Andes, S America
what degrees is oceanic plate subducted at (oceanic - continental) ?
between 30 and 70 degrees
when can earthquakes occur (oceanic-continental ) ?
as it descends, comes under pressure and friction
faulting and fracturing occur in the Benioff zone , releases lots of energy = earthquakes
what happens in oceanic oceanic ?
slightly older and denser one subducts other , creating a trench
how are island arcs formed ?
dehudration takes place cause partial melting of the matle wedge . this magma rises 2 surface and forms chains of volcanic islands
how was the island arc of Antilles formed ?
central atlantic , N american plate subducted beneath the smaller caribbean plate forming antilles
are large earthqaukes common at oceanic-oceains ?
common
at pacific ocean how many of earthquales occur here (oceanic-oceanic) ?
largely rimmed by either convergent or conservative (transform) boundaries , about 80% of all earthquakes , and many volcanoes located here
what happens at continental continental ?
two plates converge - little, if any subduction takes place
bcos they have similar denisities
how was the alps created ?
collision of african and eurasian plates over the past 40 million years has created alps
what happens at conservative plate margins ?
at some places - tectonic plates neiuther diverge or converge but rather slide past each other
what is volcanic activity like at conservative plate margins
absent
cos no subduction takes place
do earthquales happen at conservative plate margins ?
frictional reistance to movement along the plate boundaries often causes the build-up of pressure. From time to time , these pressures cause rocks to fracture releasing enormous amounts of energy as the pressure is released , causing earthquake s
what are examples of conservative plate margins ?
cali, N America and pacific plates
where are explosive volcanoes loacted ?
convergent plate boundaries
where are effusive volcanoes located ?
divergent plate boundaries
what type of lava do explosive volcanoes have ?
rhyolite (more acidic)
andesite (less acidic)
what type of lava do effusive volcanoes have?
basaltic
what are the lava characteristics of explosive volcanoes ?
acid (high % of silica ) , high visocity, lower temp at eruption
what are the lava characteristics of effusive volcanoes ?
basialtic (low % of silicon ), low visocity , higher temp at eruption
what is the style of eruption at an explosive volcano ?
violent bursting of gas bubbles when magma reaches surface , highly explosive, vent and top of cone often shattered
what is the style of eruption of effusive volcano ?
gas bubbles expand freely, limited explosive force
what materials are erupted in explosive volcano
gas, dust , ash , lavabombs , tephra
what materials are eruptes in effusive volcano ?
gas, lava flows
what are the frequency of explosive eruptions ?
tend to have long periods with no activity
what are the frequency of effusive eruptions ?
tend to be more requent, an eruption can continue or many months
what is the shaoe of an explosive volcano ?
steep sided strato volcano , caldera
what is the shape of effusive volcano ?
gently sloping sides , shield volcanoes, lava plateaux when eruption from multiple fissures
what is an icelandic lava eruption ?
characterised by persistent fissure eruption
large quantities of basaltic lava build up horizontal plains
what are Hawaiian eruptions ?
more noticeble central activity thsn icelandic . Runny, basaltic lava travels down the sides of the volcano in lava flows
gases escape easy , ocassional pyroclastics
what are strombolian eruptions ?
characterised by frequent gas explosions which blast fragments of runny lava into the air to form cones
Very explosive eruptions with large quantity of pyroclastic throughouts
what are vulcanian eruptions ?
violent gas explosions blast out plugs of sticky or cooled lava. Fragments build up into cones of ash and pumice . occurs when very viscous lava which solidifies rapidly.
often the eruption clears a blocked vent and spews large quantities of volcanic ash into atmosphere
what are vesuvian eruptions ?
very powerful blasts of gas creating ash clouds high into sky
- they are more violent tan vulcanian eruptions
ava flows occur
what are plinian eruptions ?
gas rushes up thru sticky lava and blasts ash and fragments into sky in huge explosion
violent eruptions - large clouds of gas and pyroclastic clouds can rush down slopes
part of volcano may be blasted away
what is another name for strato volcanoes ?
composite cone volcanoes
what are strato volcanoes made of ?
layers of ash and acid lava
what type of profiles do strato volcanoes have ?
concave symmetrical profiles
what do strato volcanoes contain ?
complex internal networks of lava flows which form minor igenous features such as skills and dykes
what happens with acid magma and tsrtao volcanoes ?
acid magma doesnt flow as easily
vents are often fielled with a mass of solidified magma - prevents magma from tising freely from depth -
so,,, enormous pressures can build up inside a volcano until it erupts
what is a caldera /?
volcanic craters more than 2km in diameter
how do calderas form ?
explosive eruption destroys much of the cone and underlying magma chamber is largely emptied
how large did the eruption of krakatoa in 1883 leave a caldera ?
7km wide
what are food basalts >?
when basic magma erupts from multiplw fissures, vast areas can be covered by free-flowing lava
what is an example of a lava plateaux ?
deccan plateau - central india , covers more than 500,000 km squared
what is another name for a hot spot ?
intre plate volcanoe
what is a hot spot ?
fixed area of intense volcanic activity where magma from a rising mantle plume reaches the Earth’s surface
how did hawaiian island chains form ?
they lie at centre of the pacific plate, thousands of kilometres from nearest plate boundary - so formed due to existence of hot spots
what is a super volcano ?
erupts more than 1000km cubed o material in a single eruption event
what is yellowstone supervolcano ?
wyoming
caldera = 75km diametre
what is the impact of supervolcanoes ?
Very high magnitude events is deduced from the extent and depth of ash alyers and their impact on plant , insect and animal species
what are the two key factors of measuring and assessing volcanic activity ?
magnitue
intensity
what is magnitude ?
amount of material erupted
what is intensity ?
speed at which material is erupted
what is VEI ?
volcanic explosivity index - combines magnitude and intensity into a single number on a scale of 0, the least explosive , to 8, the most explosive
Each increase in number represents nearly a ten-fold increase in explosivity
what type of lava flow is a basaltic lava flow ?
free flowing and can run considerable distances
what lava flow happened in Hawaii, july 2015 ?
lava flow extended for 20km before stopping in August the same year a flow was reported to have covered 800m in a day
what is an acidic lava flow like ?
rhyolite and thick and pasty so dont flow easily
what does lava flow destroy ?
eveyrthing in path will be burned, buried or bulldozed.
Destory infrastructure , property and crops, lava flows, rarely cause injuries or fatalities
what is a pyroclastic flow ?
combo of very hot gases (500 degrees plus) , ash and rock fragments travelling at high speed (100km/h)
Follows contours of ground and destroy everything in their path
what will happen if you inhale pyroclastic flow ?
instant death
what happened at pompeii (pyroclastic flow)?
Overhwelmed by pyroclastic flow from Mount vesuvius in AD 79
WHAT IS TEPHRA ?
describes any material ejected from a volcano in the air
Ranges in size from very fine ash to large volcanic bombs (>6cm across).
Also lighter debris = pumice
what does tephra destroy?
buries farmland in layers of ash and destroying crops
- transport distrupted both on ground and air
Buildings = collapse = weight of accumulated ash and people with respiratory diseases cant breath
how did tephra affect Eykafjallajokull ?
Apr 2010 - cancellation of 100,000 flights
what gases do volcanoes emit ?
CO2 , CO, SO2
WHAT is the impact of gases from volcanoes ?
deadly threat to human populations
so2 combines with atmospheric water, acid rain = produced
damage crops and pollute surface water and soils
what is a lahar ?
type of mudflow with consistency of wet concrete
Snow and ice on volcano summit melt during an eruption and flow rapidly down the cone
Rock fragments large and small, as well as ash and soil are mixed together
what speed do lahars travel at ?
up to 50km/h
what do lahars destory ?
everything in its path is destroyed or buried under thick layers of debris
what happened with lahars at eruption of nevado del ruiz ?
1984 - eruption of nevado del ruiz , colombian town of armero , overwhelmed by lahars, resulting in death of 23,000 people
what is volcano caused floods ?
volcanic eruptions beneath an ice field or glacier cause rapid melting
what is a jokulnlaup ?
ICELAND - several active volcanoes lie under the vasnajokull ice accumulate until they find an exit from under the ice.
resulting torrent of water is known as a jokulnlaup
what is a tsunami ?
violent eruptions of some island volcanoes can cause massive displacement of ocean water and tsunami waves capable of travelling at speeds of up to 600km/h.
Deep water = height that is usually less than 1m and very long wavelength up to 200km.
Approaching shore, tsunami waves increase rapidly in height AND WHEN THEY BREAK transfer vast amount of energy and water along the shore and island
what was the tsunami at krakatoa ?
1883 - drowned 36,000 people
how did the eruption of supervolcano toba , indonesia impact long term ?
climate change
led to reductions in global temp as ash blocked sunlight from reaching earth’s surface
how does eruptions impact climate chnage
?
emitt large quantaties of ash
release of so2 - added to cooling ‘mixed with water in atmos so2 forms sulphuric acid - which reflects insolation
