Assess the contribution of plate-tectonic theory to our knowledge of the Earth’s structure
The theory of plate tectonics has been pivotal in advancing our understanding of the Earth's internal
and surface structure. Building on the earlier hypothesis of continental drift, it offers a unifying
framework explaining the movement of lithospheric plates over the asthenosphere, driven by
mantle convection. It has clarified the distribution of geophysical phenomena such as earthquakes
and volcanic activity and it has deepened our insight into the Earth's internal layering.
The lithosphere is broken up into seven major and several minor parts – called tectonic plates – that
move relative to each other over the asthenosphere. It is this movement that causes earthquakes
and volcanic eruptions. Tectonic plates are large, irregularly shaped slabs of solid rock that vary
greatly in size and move slowly (about 2 cm to 5 cm a year) .The study of these plates is called plate-
tectonic theory, and their movement is driven by a number of different processes. The first process
is mantle convention which has long been thought responsible for plate movement, but this
argument is now less accepted. In mantle convection, heat produced by the decay of radioactive
elements in the Earth’s core heats the lower mantle – creating convection currents. These hot, liquid
magma currents are thought to move in circles in the asthenosphere – thus, causing the plates to
move. All of these factors show the importance of plate theory in explaining the knowledge of the
earth’s structure.
Additionally there is slab pull which is increasingly being seen as a major driving force for
plate movement. Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it
cools. This causes it to sink into the mantle under its own weight – pulling the rest of the plate
further down with it. Additionally, there is subduction where two oceanic plates (or an oceanic plate
and a continental plate) move towards each other, one slides under the other into the mantle –
where it melts in an area known as a subduction zone. Finally there is seafloor spreading where
in the middle of many oceans are huge mid-ocean ridges, or underwater mountain ranges. These are
formed when hot magma (molten rock) is forced up from the asthenosphere and hardens – forming
new oceanic crust. This new crust pushes the tectonic plates apart in a process called seafloor
spreading. All of these factors further demonstrate the importance of plate theory
Plate tectonic theory also helps further explain plate boundaries and how they work. At destructive
plate margins the plates move towards each other (converge). At constructive plate margins, two
plates are moving apart (diverging) which leads to the formation of new crust. In oceans, this
divergence forms mid ocean ridges (such as the mid-Atlantic ridge) and on continents It forms rift
valleys (such as the East African rift valley). Finaly the last plate boundary which plate tectonic theory
helps explain are conservative plate boundaries which is when along some boundaries, two plates
slide past each other forming the margin. This results in a major break in the crust between them as
they fault, and where it occurs on a transform fault, which affects a wider area. Although no crust is
made or destroyed here(and there is no volcanic activity), this type of plate margin is tectonically
very active and can be associated with powerful earthquakes. The two plates sometimes stick as
they move past each other, causing stress and pressure to build up, which is suddenly released as a
strong shallow focus earthquake. One of the most famous conservative plate margins is the San
Andreas Fault in California, which has generated significant earthquakes.
In conclusion, Plate theory is very important in helping us understand the earth’s structure through
mantle convection, slab pull, subduction, seafloor spreading and also the plate boundaries
themselves and how they work in relation to the earth’s structure.
, Assess the relative importance of physical factors and processes in explaining the impacts of volcanic eruptions. (12)
Volcanic eruptions are complex geological events which are shaped by various physical factors, characteristics
and processes. Different factors such as the location of the volcano, the type of plate boundary and the type of
volcano and magma can all explain the impacts of volcanoes and how impactful they are.
One of the most significant physical factors in explaining the impact of volcanic eruptions is the location of the
volcano, as it can determine the type and severity of secondary hazards, such as lahars, tsunamis, and
jökulhlaups. For example, Eyjafjallajökull (Iceland, 2010) is located beneath a glacier, which led to rapid
melting of ice during the eruption and triggered jökulhlaups—glacial outburst floods. These flooded large
areas, destroyed infrastructure, and made emergency response difficult. The eruption also ejected a massive
ash cloud into the jet stream, grounding over 100,000 flights and causing $1.7 billion in global airline losses—
highlighting how its high-latitude location influenced ash distribution across Europe. In contrast, Montserrat,
situated in the tropical Caribbean, suffers from intense rainfall which mixes with ash to form lahars. During the
eruption in Monserrat, lahars buried parts of the island including the capital Plymouth, which was covered in
up to 12 metres of volcanic material. Over 7,000 residents were permanently displaced, demonstrating how a
humid, mountainous island location exacerbated impacts long after the initial eruption. Additionally, volcanoes
closer to the sea are prone to tsunamis such as the Anak Krakatau eruption (2018) which caused a flank
collapse into the sea, triggering a tsunami that killed 430 people in Indonesia—showing how coastal settings
can transform eruptions into multi-hazard events. Therefore, these factors demonstrate how the location can
strongly explain the impacts of volcanic eruptions.
Furthermore, another factor which explains the impacts of volcanoes is the type of volcano which determines
the lava type, affecting how destructive it is. Shield volcanoes, such as those found in Iceland, have low-
viscosity basaltic lava that flows easily and results in effusive eruptions with lower explosivity. During the
Eyjafjallajökull eruption, although the lava itself wasn’t deadly, the explosive interaction between magma and
ice produced ash that disrupted international air travel (as already mentioned). However, impacts on life and
property in Iceland were relatively low due to the shield volcano’s structure. In contrast, composite volcanoes
like Mount Merapi (Indonesia) and Montserrat have steep sides and viscous andesitic lava, which traps gas,
building up pressure that often results in explosive eruptions and pyroclastic flows. At Mount Merapi (2010), a
VEI-4 eruption released pyroclastic flows that travelled 15 km from the summit, killing 353 people and
displacing over 350,000. Similarly, Montserrat's pyroclastic flows destroyed Plymouth and reshaped the
southern half of the island. The composite cone shape and thick lava not only produce more violent eruptions
but make evacuation more difficult due to steeper slopes and rapid flow speeds. Thus, the volcano type
directly affects the magnitude and kind of hazard produced demonstrating how the type of volcano and lava
composition are key physical factors in understanding volcanic impacts.
Finally the last physical factor are the tectonic boundary on which a volcano sits on as it influences its
explosiveness and hazard potential. Destructive plate boundaries, particularly subduction zones, often produce
highly viscous magma due to melting of oceanic crust in the Benioff Zone, which leads to gas-rich, explosive
eruptions. For example, Mount St Helens (USA, 1980) was on a destructive margin where the Juan de Fuca
plate subducts under the North American plate and it exploded laterally after a bulge collapse, releasing a
pyroclastic flow travelling at 500 km/h and killing 57 people. Similarly, Mount Merapi, on the subduction
boundary between the Indo-Australian and Eurasian plates, has a complex lava dome system that collapses,
causing repeated explosive events. In contrast, constructive boundaries, such as the Mid-Atlantic Ridge
running through Iceland, typically produce basaltic magma with low viscosity, leading to gentle lava flows
rather than catastrophic explosions and the Eyjafjallajökull had 0 causalities due to it’s gentler lava flows which
came about due to the constructive boundaries. All of these factors demonstrate how the plate boundaries
can heavily impact volcanic eruptions influencing the explosiveness of them.
In conclusion, physical factors and processes are very important in explaining the impacts of volcanic
eruptions. The most important physical factor in explaining the impact of volcanic eruptions is the location of
the volcano as it can drastically affect the destructiveness of a volcano, through the secondary hazards that it
influences (e.g. Lahars). However, all physical factors such as plate boundaries and the type of volcano help
explain the impacts of volcanic eruptions.
The theory of plate tectonics has been pivotal in advancing our understanding of the Earth's internal
and surface structure. Building on the earlier hypothesis of continental drift, it offers a unifying
framework explaining the movement of lithospheric plates over the asthenosphere, driven by
mantle convection. It has clarified the distribution of geophysical phenomena such as earthquakes
and volcanic activity and it has deepened our insight into the Earth's internal layering.
The lithosphere is broken up into seven major and several minor parts – called tectonic plates – that
move relative to each other over the asthenosphere. It is this movement that causes earthquakes
and volcanic eruptions. Tectonic plates are large, irregularly shaped slabs of solid rock that vary
greatly in size and move slowly (about 2 cm to 5 cm a year) .The study of these plates is called plate-
tectonic theory, and their movement is driven by a number of different processes. The first process
is mantle convention which has long been thought responsible for plate movement, but this
argument is now less accepted. In mantle convection, heat produced by the decay of radioactive
elements in the Earth’s core heats the lower mantle – creating convection currents. These hot, liquid
magma currents are thought to move in circles in the asthenosphere – thus, causing the plates to
move. All of these factors show the importance of plate theory in explaining the knowledge of the
earth’s structure.
Additionally there is slab pull which is increasingly being seen as a major driving force for
plate movement. Newly formed oceanic crust at mid-ocean ridges becomes denser and thicker as it
cools. This causes it to sink into the mantle under its own weight – pulling the rest of the plate
further down with it. Additionally, there is subduction where two oceanic plates (or an oceanic plate
and a continental plate) move towards each other, one slides under the other into the mantle –
where it melts in an area known as a subduction zone. Finally there is seafloor spreading where
in the middle of many oceans are huge mid-ocean ridges, or underwater mountain ranges. These are
formed when hot magma (molten rock) is forced up from the asthenosphere and hardens – forming
new oceanic crust. This new crust pushes the tectonic plates apart in a process called seafloor
spreading. All of these factors further demonstrate the importance of plate theory
Plate tectonic theory also helps further explain plate boundaries and how they work. At destructive
plate margins the plates move towards each other (converge). At constructive plate margins, two
plates are moving apart (diverging) which leads to the formation of new crust. In oceans, this
divergence forms mid ocean ridges (such as the mid-Atlantic ridge) and on continents It forms rift
valleys (such as the East African rift valley). Finaly the last plate boundary which plate tectonic theory
helps explain are conservative plate boundaries which is when along some boundaries, two plates
slide past each other forming the margin. This results in a major break in the crust between them as
they fault, and where it occurs on a transform fault, which affects a wider area. Although no crust is
made or destroyed here(and there is no volcanic activity), this type of plate margin is tectonically
very active and can be associated with powerful earthquakes. The two plates sometimes stick as
they move past each other, causing stress and pressure to build up, which is suddenly released as a
strong shallow focus earthquake. One of the most famous conservative plate margins is the San
Andreas Fault in California, which has generated significant earthquakes.
In conclusion, Plate theory is very important in helping us understand the earth’s structure through
mantle convection, slab pull, subduction, seafloor spreading and also the plate boundaries
themselves and how they work in relation to the earth’s structure.
, Assess the relative importance of physical factors and processes in explaining the impacts of volcanic eruptions. (12)
Volcanic eruptions are complex geological events which are shaped by various physical factors, characteristics
and processes. Different factors such as the location of the volcano, the type of plate boundary and the type of
volcano and magma can all explain the impacts of volcanoes and how impactful they are.
One of the most significant physical factors in explaining the impact of volcanic eruptions is the location of the
volcano, as it can determine the type and severity of secondary hazards, such as lahars, tsunamis, and
jökulhlaups. For example, Eyjafjallajökull (Iceland, 2010) is located beneath a glacier, which led to rapid
melting of ice during the eruption and triggered jökulhlaups—glacial outburst floods. These flooded large
areas, destroyed infrastructure, and made emergency response difficult. The eruption also ejected a massive
ash cloud into the jet stream, grounding over 100,000 flights and causing $1.7 billion in global airline losses—
highlighting how its high-latitude location influenced ash distribution across Europe. In contrast, Montserrat,
situated in the tropical Caribbean, suffers from intense rainfall which mixes with ash to form lahars. During the
eruption in Monserrat, lahars buried parts of the island including the capital Plymouth, which was covered in
up to 12 metres of volcanic material. Over 7,000 residents were permanently displaced, demonstrating how a
humid, mountainous island location exacerbated impacts long after the initial eruption. Additionally, volcanoes
closer to the sea are prone to tsunamis such as the Anak Krakatau eruption (2018) which caused a flank
collapse into the sea, triggering a tsunami that killed 430 people in Indonesia—showing how coastal settings
can transform eruptions into multi-hazard events. Therefore, these factors demonstrate how the location can
strongly explain the impacts of volcanic eruptions.
Furthermore, another factor which explains the impacts of volcanoes is the type of volcano which determines
the lava type, affecting how destructive it is. Shield volcanoes, such as those found in Iceland, have low-
viscosity basaltic lava that flows easily and results in effusive eruptions with lower explosivity. During the
Eyjafjallajökull eruption, although the lava itself wasn’t deadly, the explosive interaction between magma and
ice produced ash that disrupted international air travel (as already mentioned). However, impacts on life and
property in Iceland were relatively low due to the shield volcano’s structure. In contrast, composite volcanoes
like Mount Merapi (Indonesia) and Montserrat have steep sides and viscous andesitic lava, which traps gas,
building up pressure that often results in explosive eruptions and pyroclastic flows. At Mount Merapi (2010), a
VEI-4 eruption released pyroclastic flows that travelled 15 km from the summit, killing 353 people and
displacing over 350,000. Similarly, Montserrat's pyroclastic flows destroyed Plymouth and reshaped the
southern half of the island. The composite cone shape and thick lava not only produce more violent eruptions
but make evacuation more difficult due to steeper slopes and rapid flow speeds. Thus, the volcano type
directly affects the magnitude and kind of hazard produced demonstrating how the type of volcano and lava
composition are key physical factors in understanding volcanic impacts.
Finally the last physical factor are the tectonic boundary on which a volcano sits on as it influences its
explosiveness and hazard potential. Destructive plate boundaries, particularly subduction zones, often produce
highly viscous magma due to melting of oceanic crust in the Benioff Zone, which leads to gas-rich, explosive
eruptions. For example, Mount St Helens (USA, 1980) was on a destructive margin where the Juan de Fuca
plate subducts under the North American plate and it exploded laterally after a bulge collapse, releasing a
pyroclastic flow travelling at 500 km/h and killing 57 people. Similarly, Mount Merapi, on the subduction
boundary between the Indo-Australian and Eurasian plates, has a complex lava dome system that collapses,
causing repeated explosive events. In contrast, constructive boundaries, such as the Mid-Atlantic Ridge
running through Iceland, typically produce basaltic magma with low viscosity, leading to gentle lava flows
rather than catastrophic explosions and the Eyjafjallajökull had 0 causalities due to it’s gentler lava flows which
came about due to the constructive boundaries. All of these factors demonstrate how the plate boundaries
can heavily impact volcanic eruptions influencing the explosiveness of them.
In conclusion, physical factors and processes are very important in explaining the impacts of volcanic
eruptions. The most important physical factor in explaining the impact of volcanic eruptions is the location of
the volcano as it can drastically affect the destructiveness of a volcano, through the secondary hazards that it
influences (e.g. Lahars). However, all physical factors such as plate boundaries and the type of volcano help
explain the impacts of volcanic eruptions.
