-Hazardous Earth
1. What is the evidence for continental drift and plate tectonics?
Theories of continental drift and plate tectonics including:
• the basic structure of the Earth including the lithosphere,
asthenosphere and the role of convection currents
Thickness (km) Density Mineral
(km/m^3) composition
Crust Continental Continental Continental
Mean: 35 2.6- 2.7 Granitic, Sial
Min <30 Oceanic 3 Oceanic
Max: 70 Basaltic Sima
Oceanic
5-10
mantle To a depth of 3.3 at moho Rich in
2900km 5.6 at core magnesium
and iron
Moho- boundary between the Earth’s crust and its mantle (35km
continental) (7 km oceanic). In geology, the word "discontinuity" is
used for a surface at which seismic waves change velocity.
Lithosphere- between crust and asthenosphere, this is rigid. Difficult
to understand the difference between this and asthenosphere. This
and crust make the plates.
Asthenosphere- 100 km- 300 km down, solid but flows under
pressure
Convection currents- In the mantle, heat from Earth’s core drives
convection currents, causing magma to rise, solidify at the crust,
and sink back into the mantle. It drives the movement of tectonic
plates, leading to processes like seafloor spreading, subduction, and
continental drift.
• evidence for seafloor spreading; palaeomagnetism; the age
of sea floor rocks
In 1801 German geographer Alexander von Humboldt wrote about
the fit of south America and west Africa, however this idea was not
developed until later.
In 1912 Alfred Wegener a meteorologist talked that 250 million
years ago a single continent Pangea existed which slowly broke into
two, this continued to the look today. However, this was rejected as
he was not a geologist.
Palaeomagnetism- Echo sounders discovered a pattern of repeating
stripes as you moved away from the mid-Atlantic ridge. This has iron
, filings that showed the polarity at the time of creation (changes
every 400,000-500,00 years). The age of the rocks became older as
you went away, proof of this process. Sea floor spreading is the
mechanism that occurs to create this. Fresh molten rock is pushed
from the asthenosphere and the older rock is pushed away in a
conveyer belt, eventually this is subducted into the asthenosphere
and becomes semi molten.
• evidence from ancient glaciations
Evidence of ice sheets in the tropics (Africa, South America, India,
Australia), even though during earths coldest period it was
impossible for ice to be formed there unless closer to the poles.
Tropical plant remains of coal deposits in Antarctica.
• fossil records
Rocks that have the same characteristics found thousands of miles
away from each other (same structure and composition in Wales and
east US)
Mesosaurus- prehistoric water amphibian with fossils found in south
America and south Africa
Lystrosaurus- larger mammal with fossils found in Africa, India and
Antarctica (cannot swim nor fly)
Glossopteris- fossils of this fern found in all southern continents (too
heavy to be carried by wind nor water)
Earth’s crustal features and processes, including:
• the global pattern of plates and plate boundaries
seismometers from military purposes showed that most earthquakes
were concentrated in narrow bands, this suggested that ridged
lithosphere and crust were broken into tectonic plates and not
static, some places moving apart and others converging.
• the features and processes associated with divergent
(constructive) plate boundaries
moving apart has magma rising through the asthenosphere and
forcing its way to the surface, most notable at mid ocean ridges.
Consist of long chains of mountains that are broken into transform
faults. Eruptions here cause pillow lava (magma rises and pressure
reduces and liquefies and fractures) (Iceland). Mid ocean ridges
cause superheated jets of water (black smokers).
Rift away from mid oceanic ridges:
Boundary type Rate of spread Landforms Example
(cm)
Fast 16.5 Broad East pacific
mountains, no rise
rift valleys
, Medium 5- 10 Poorly defined Galapagos
rift valleys and ridge
smooth
mountains
Slow 2-3 Steep Mid Atlantic
mountains and ridge
clear rift
valleys
Rift zones are not confined to the ocean floor, occurs with thin
continental crust (red sea towards turkey- graben, eventually sank).
• the features and processes associated with convergent plate
boundaries including oceanic-continental, oceanic-oceanic
(destructive) and continental-continental (collision)
boundaries
oceanic-continental- subduction causes ocean trench, volcanoes,
fold mountains. Slab pull occurs at 30 to 70 degrees, due to the
pressure faulting and fracturing occur in the Benioff zone, causes
earthquakes. (Andes) due to the amount of water, when
temperatures increase dehydration occurs which partially melt the
overlying plate causing plutons of magma therefore fold mountains
and volcanoes.
Oceanic-oceanic- older and denser one subducts therefore a trench,
dehydration occurs and causes island arcs (central Atlantic and
north American cause Antilles) large earthquakes common.
Continental-continental- little subduction due to similar densities
(African and Eurasian caused alps)
• the features and processes associated with conservative
plate boundaries
slide past each other with no volcanic activity however build-up of
pressure cause earthquakes when released. No landforms, however,
cause giant tear, strata may be visible, drainage may be modified as
rivers are deflected (north American and pacific, California)
2. What are the main hazards generated by volcanic activity?
Lava can be classified into basaltic (fluid, low SiO2), andesitic (med SiO2),
and rhyolitic (thick, high SiO2).
Different types of volcanoes to investigate their causes and
features including:
• explosive eruptions (higher viscosity and gas magma)
located at convergent (destructive) plate boundaries
Strato-volcanoes made from layers of ash are concave and
symmetrical with sills and dykes. Due to it not flowing, vents are
often filled with solidified magma and blows its caps off when
1. What is the evidence for continental drift and plate tectonics?
Theories of continental drift and plate tectonics including:
• the basic structure of the Earth including the lithosphere,
asthenosphere and the role of convection currents
Thickness (km) Density Mineral
(km/m^3) composition
Crust Continental Continental Continental
Mean: 35 2.6- 2.7 Granitic, Sial
Min <30 Oceanic 3 Oceanic
Max: 70 Basaltic Sima
Oceanic
5-10
mantle To a depth of 3.3 at moho Rich in
2900km 5.6 at core magnesium
and iron
Moho- boundary between the Earth’s crust and its mantle (35km
continental) (7 km oceanic). In geology, the word "discontinuity" is
used for a surface at which seismic waves change velocity.
Lithosphere- between crust and asthenosphere, this is rigid. Difficult
to understand the difference between this and asthenosphere. This
and crust make the plates.
Asthenosphere- 100 km- 300 km down, solid but flows under
pressure
Convection currents- In the mantle, heat from Earth’s core drives
convection currents, causing magma to rise, solidify at the crust,
and sink back into the mantle. It drives the movement of tectonic
plates, leading to processes like seafloor spreading, subduction, and
continental drift.
• evidence for seafloor spreading; palaeomagnetism; the age
of sea floor rocks
In 1801 German geographer Alexander von Humboldt wrote about
the fit of south America and west Africa, however this idea was not
developed until later.
In 1912 Alfred Wegener a meteorologist talked that 250 million
years ago a single continent Pangea existed which slowly broke into
two, this continued to the look today. However, this was rejected as
he was not a geologist.
Palaeomagnetism- Echo sounders discovered a pattern of repeating
stripes as you moved away from the mid-Atlantic ridge. This has iron
, filings that showed the polarity at the time of creation (changes
every 400,000-500,00 years). The age of the rocks became older as
you went away, proof of this process. Sea floor spreading is the
mechanism that occurs to create this. Fresh molten rock is pushed
from the asthenosphere and the older rock is pushed away in a
conveyer belt, eventually this is subducted into the asthenosphere
and becomes semi molten.
• evidence from ancient glaciations
Evidence of ice sheets in the tropics (Africa, South America, India,
Australia), even though during earths coldest period it was
impossible for ice to be formed there unless closer to the poles.
Tropical plant remains of coal deposits in Antarctica.
• fossil records
Rocks that have the same characteristics found thousands of miles
away from each other (same structure and composition in Wales and
east US)
Mesosaurus- prehistoric water amphibian with fossils found in south
America and south Africa
Lystrosaurus- larger mammal with fossils found in Africa, India and
Antarctica (cannot swim nor fly)
Glossopteris- fossils of this fern found in all southern continents (too
heavy to be carried by wind nor water)
Earth’s crustal features and processes, including:
• the global pattern of plates and plate boundaries
seismometers from military purposes showed that most earthquakes
were concentrated in narrow bands, this suggested that ridged
lithosphere and crust were broken into tectonic plates and not
static, some places moving apart and others converging.
• the features and processes associated with divergent
(constructive) plate boundaries
moving apart has magma rising through the asthenosphere and
forcing its way to the surface, most notable at mid ocean ridges.
Consist of long chains of mountains that are broken into transform
faults. Eruptions here cause pillow lava (magma rises and pressure
reduces and liquefies and fractures) (Iceland). Mid ocean ridges
cause superheated jets of water (black smokers).
Rift away from mid oceanic ridges:
Boundary type Rate of spread Landforms Example
(cm)
Fast 16.5 Broad East pacific
mountains, no rise
rift valleys
, Medium 5- 10 Poorly defined Galapagos
rift valleys and ridge
smooth
mountains
Slow 2-3 Steep Mid Atlantic
mountains and ridge
clear rift
valleys
Rift zones are not confined to the ocean floor, occurs with thin
continental crust (red sea towards turkey- graben, eventually sank).
• the features and processes associated with convergent plate
boundaries including oceanic-continental, oceanic-oceanic
(destructive) and continental-continental (collision)
boundaries
oceanic-continental- subduction causes ocean trench, volcanoes,
fold mountains. Slab pull occurs at 30 to 70 degrees, due to the
pressure faulting and fracturing occur in the Benioff zone, causes
earthquakes. (Andes) due to the amount of water, when
temperatures increase dehydration occurs which partially melt the
overlying plate causing plutons of magma therefore fold mountains
and volcanoes.
Oceanic-oceanic- older and denser one subducts therefore a trench,
dehydration occurs and causes island arcs (central Atlantic and
north American cause Antilles) large earthquakes common.
Continental-continental- little subduction due to similar densities
(African and Eurasian caused alps)
• the features and processes associated with conservative
plate boundaries
slide past each other with no volcanic activity however build-up of
pressure cause earthquakes when released. No landforms, however,
cause giant tear, strata may be visible, drainage may be modified as
rivers are deflected (north American and pacific, California)
2. What are the main hazards generated by volcanic activity?
Lava can be classified into basaltic (fluid, low SiO2), andesitic (med SiO2),
and rhyolitic (thick, high SiO2).
Different types of volcanoes to investigate their causes and
features including:
• explosive eruptions (higher viscosity and gas magma)
located at convergent (destructive) plate boundaries
Strato-volcanoes made from layers of ash are concave and
symmetrical with sills and dykes. Due to it not flowing, vents are
often filled with solidified magma and blows its caps off when
