Geography Class 15
Extrusive Volcanic landforms (continued)
- Volcanic cones:
- Diagramatic representation of Volcanic cones:
- Shield volcano:
- It is formed from eruptions of very fluid basaltic magma.
- It is formed along hotspots due to mantle plumes.
- They are the largest of all volcanoes.
- They are not very steep.
- Examples Mauna Leo and Mauna Kea.
- Ash-cinder volcano:
- They are formed due to the accumulation of loose particles around the vent.
- They are dominated by ash, debris, and other volcanic material with less lava.
- An example includes the Taal volcano in the Philippines.
- Composite volcano:
- They are formed due to the accumulation of viscous lava which is of lower fluidity.
- The alternating layers of ash and lava provide for composite structure.
- They are one of the steepest of all types of volcanoes.
- For Example Mount Fuji in Japan, Krakatoa, etc.
- Crater:
- It is a funnel-shaped depression formed at the mouth of the volcano.
- The crater filled with water results in the formation of a crater lake.
- Caldera:
- It is a greatly enlarged depression resulting from the violent eruption volcano resulting in the subsidence of much of the Volcano.
- When water is filled it results in the caldera lake.
- Flood basalt province:
- When a highly fluid basaltic magma erupts over a plateau region it flows for a long distance covering large areas and creating a flood basalt province
- For example, the Deccan province and the Columbian plateau.
- Hot springs/thermal springs:
- When water sinks deep enough beneath the surface to be heated by a hot spot or a magma chamber or a geothermal belt it rises to the surface continuously without any explosion.
- Water from hot springs contains dissolved minerals with medicinal value.
- For example, the hot springs in USA, Iceland, and India (Rajgir, Manikaran, Manali, etc).
- Geysers:
- They are the fountains of hot water and superheated steam, ejected at regular intervals with explosions.
- For example Geysers of Iceland, New Zealand, USA(Old faithful Geysers)
- Fumarole:
- It involved continuous jet-like emission of steam and other gases.
- For example Fumarole in Iceland.
- Mud volcano:
- It involves the eruption of mud mixed with water and gases.
- They may not contain magma.
- For example Baratang island of Andaman and Nicobar.
Intrusive features of Volcanism
- These are the landforms that are formed inside the earth's surface as manga cools down below the surface.
- Diagrammatic representation of Extrusive volcanic landforms:
- Batholiths:
- It is a long irregular dome-shaped structure.
- They are large bodies formed by the cooling of magma along deeper layers of the lithosphere.
- Laccoliths:
- It is a mushroom-shaped feature formed due to the intrusion of magma.
- It maintains contact with the magma chamber.
- Lopoliths:
- When the magma solidifies along a saucer-shaped depression it results in lopoliths.
- Sill:
- These are formed due to the cooling of magma along horizontal bedding planes.
- Dykes:
- These are vertical wall-like structures formed by the cooling of magma.
Geomagnetism
- The magnetic field associated with the earth is called geomagnetism.
- Earth has an outer rocky mantle, below which there is the liquid outer core that surrounds the solid inner core.
- It is considered that the motion of iron charges in the liquid parts of the earth's core generates a Magnetic field.
- The motion of iron-charged particles is caused:
- Rotation of earth.
- A convection current of molten material is generated in the outer core due to heat released from the earth's inner core.
- The motion of ions in this molten material produces an electric current through the earth's core that results in a magnetic field around the earth called geomagnetism.
- Palaeomagnetism and Polar wandering:
- It is the historical study of earth magnetism through rock called Paleomagnetism.
- When the ingenious manga crystallizes, the crystal of ferromagnetic minerals such as iron, titanium, etc acquires stable magnetism which becomes frozen as the magma cools down.
- This acquired magnetism is called fossil magnetism.
- Such rocks will have ferromagnetic minerals aligned in the same direction as that of the geomagnetic field at the time of its consolidation.
- When paleomagnetic pieces of evidence for a given region were checked over a long period a gradual change in direction was detected.
- It shows that the position of magnetic poles has moved over of period, this movement is called polar wandering.
- During the study of the oceanic surface, some of the rocks were found pointing toward the north and some toward the south.
- It is inferred that the rocks can not change the polarity but it is the earth's magnetic field that reveres its polarity.
- Such a reversal of magnetic field can be brought by the reversal of convection currents in the outer core.
- The magnetic reversal occurs every 2,00,000-300,000 years.
- Aurora:
- The magnetosphere of the earth's atmosphere blocks the charged particles from solar winds.
- But some of these charged particles get trapped near polar regions where the magnetic lines are straight.
- Due to the interactions of charged particles in the earth's atmosphere near polar regions, colourful lights are released called aurora.
- It is called Aurora Borealis in the northern region and Aurora Australis in the southern region.
Earthquakes
- The vibration or oscillation felt near to the earth's surface due to transient disturbance of the elastic or gravitational equilibrium of the rocks at or beneath the surface of the earth.
- The various causes of earthquakes are:
- Plate movements.
- Minning.
- Reservoir-induced seismicity(RIS).
The topic of the next class: Earthquake to continue.
What type of magma forms a shield volcano?
Very fluid basaltic magma.
Where are shield volcanoes typically formed?
Along hotspots due to mantle plumes.
Which volcanoes are the largest of all?
Shield volcanoes.
Give an example of a shield volcano.
Mauna Loa and Mauna Kea.
What dominates the composition of ash-cinder
volcanoes?
Ash, debris, and other volcanic material with less
lava.
Give an example of an ash-cinder volcano.
Taal volcano in the Philippines.
How are composite volcanoes formed?
By the accumulation of viscous lava with
alternating layers of ash and lava.
What is one of the steepest types of volcanoes?
Composite volcanoes.
Give an example of a composite volcano.
Mount Fuji in Japan.
What is a crater in volcanic terms?
A funnel-shaped depression at the mouth of the
volcano.
What results when a crater is filled with water?
A crater lake.
What is a caldera?
A greatly enlarged depression formed by the violent
eruption and subsidence of a volcano.
What results when a caldera is filled with water?
A caldera lake.
What creates a flood basalt province?
Highly fluid basaltic magma erupting over a plateau
region and covering large areas.
Give an example of a flood basalt province.
The Deccan province and the Columbian plateau.
What causes hot springs or thermal springs?
Water sinking deep enough to be heated by a hot
spot, magma chamber, or geothermal belt and rising to the surface continuously.
What is the medicinal significance of water from
hot springs?
It contains dissolved minerals with medicinal
value.
Give an example of a hot spring.
Hot springs in USA, Iceland, and India (Rajgir,
Manikaran, Manali).
What are geysers?
Fountains of hot water and superheated steam ejected
at regular intervals with explosions.
Give an example of a geyser.
Old Faithful Geyser in the USA.
What is a fumarole?
Continuous jet-like emission of steam and other
gases.
Give an example of a fumarole.
Fumarole in Iceland.
What is a mud volcano?
An eruption of mud mixed with water and gases,
which may not contain magma.
Give an example of a mud volcano.
Baratang Island of Andaman and Nicobar.
What are intrusive features of volcanism?
Landforms formed inside the earth's surface as
magma cools down below the surface.
What is a batholith?
A long irregular dome-shaped structure formed by
the cooling of magma in deeper layers of the lithosphere.
What is a laccolith?
A mushroom-shaped feature formed due to the
intrusion of magma, maintaining contact with the magma chamber.
What is a lopolith?
A saucer-shaped depression formed by the
solidification of magma.
What is a sill?
A horizontal bedding plane formed by the cooling of
magma.
What is a dyke?
A vertical wall-like structure formed by the
cooling of magma.
What is geomagnetism?
The magnetic field associated with the earth.
What generates the magnetic field in geomagnetism?
The motion of iron charges in the liquid outer
core.
What causes the motion of iron-charged particles in
the earth's core?
Rotation of the earth and convection currents in
the outer core.
What is paleomagnetism?
The historical study of earth's magnetism through
rocks.
What is fossil magnetism?
Stable magnetism acquired by ferromagnetic minerals
in rocks as they cool down.
What is polar wandering?
The movement of the position of magnetic poles over
a period.
What is inferred from rocks pointing toward
different magnetic poles?
The earth's magnetic field reverses its polarity.
How often does magnetic reversal occur?
Every 200,000 to 300,000 years.
What is aurora?
Colorful lights released due to the interaction of
charged particles in the earth's atmosphere near polar regions.
What are the northern and southern auroras called?
Aurora Borealis (northern) and Aurora Australis
(southern).
1.Describe
the different types of volcanic cones and provide examples of each.
Answer:
Volcanic
cones are landforms created by the accumulation of volcanic materials around a
vent. They vary in shape, size, and composition, and include:
- Shield Volcanoes: These are formed by
eruptions of very fluid basaltic magma. The lava flows easily and spreads
out over large areas, resulting in broad, gently sloping sides. Shield
volcanoes are typically found along hotspots due to mantle plumes. They
are the largest of all volcanoes but have relatively gentle slopes.
Notable examples include Mauna Loa and Mauna Kea in Hawaii. Their broad,
shield-like shape is due to the low viscosity of basaltic lava, which
allows it to travel great distances before solidifying.
- Ash-Cinder Volcanoes: These volcanoes are
characterized by the accumulation of loose volcanic debris around the
vent, including ash, cinders, and volcanic rocks, with relatively less
lava flow. The resulting cone is steep-sided but generally smaller than
shield volcanoes. An example of an ash-cinder volcano is Taal Volcano in
the Philippines. These volcanoes often produce explosive eruptions that
throw ash and cinders into the air.
- Composite Volcanoes: Also known as
stratovolcanoes, these are formed from alternating layers of viscous lava
and volcanic ash. The lava has a higher viscosity, leading to steeper
slopes and more explosive eruptions. Composite volcanoes are often found
at convergent plate boundaries where an oceanic plate subducts beneath a
continental plate. Examples include Mount Fuji in Japan and Krakatoa in
Indonesia. Their layered structure results from the alternating eruptions
of lava flows and pyroclastic materials.
2.
Explain the formation of a caldera and provide examples of calderas around the
world.
Answer:
A caldera
is a large, bowl-shaped depression formed when a volcano erupts violently,
causing the summit or a large portion of the volcano to collapse into the
emptied magma chamber beneath. The process typically involves a massive
eruption that expels a substantial amount of magma and volcanic material,
leading to the structural collapse of the volcano. The resulting depression is
often filled with water, forming a caldera lake.
Notable
examples of calderas include:
- Yellowstone Caldera in the United States: This
caldera, located in Wyoming, is one of the largest active calderas in the
world. It was formed by several massive volcanic eruptions over the past 2
million years.
- Crater Lake in Oregon, USA: Formed by
the collapse of Mount Mazama, this caldera is now filled with water,
creating the deepest lake in the United States.
- Santorini Caldera in Greece: This caldera was
created by a massive eruption around 3,600 years ago, which led to the
collapse of the Minoan volcanic island. It is now partially submerged and
features a series of small islands within the caldera.
3.
Discuss the role and characteristics of geysers in volcanic regions. Provide
examples of notable geysers.
Answer:
Geysers
are a type of hot spring that periodically ejects bursts of hot water and
steam. This phenomenon occurs when groundwater is heated by underlying magma or
geothermal activity, causing it to build up pressure until it is expelled
through the surface. Geysers require specific geological conditions to form,
including an underground reservoir of water, a heat source, and a plumbing
system that allows for pressure build-up.
Characteristics
of geysers include:
- Periodic Eruptions: Geysers erupt at regular intervals,
which can range from minutes to hours or even days, depending on the
specific geyser's plumbing and geothermal conditions.
- Hot Water and Steam: The eruptions typically
involve a mix of superheated water and steam, which can shoot high into
the air.
Notable
examples of geysers include:
- Old Faithful in Yellowstone National
Park, USA: This is one of the most famous and predictable geysers, with
eruptions occurring approximately every 90 minutes.
- Geysers of Iceland: Iceland is home to several
notable geysers, including Strokkur, which erupts every few minutes,
shooting water up to 20 meters high.
- Waimangu Volcanic Valley in New Zealand: This area
features several geysers and geothermal features, including the active
geyser known as "Inferno Crater."
4.
Describe the features and formation of flood basalt provinces. Include examples
of such provinces.
Answer:
Flood
basalt provinces are extensive volcanic regions formed by the eruption of
highly fluid basaltic magma that spreads out over large areas, creating a thick
layer of basalt lava. These eruptions are characterized by the outpouring of
lava from fissures rather than central vents, which allows the lava to flow
across vast regions.
Characteristics
of flood basalt provinces include:
- Large Extent: The lava flows cover
thousands of square kilometers, creating a vast, relatively flat volcanic
plateau.
- Fluid Lava: The basaltic magma is very
fluid, allowing it to travel long distances from the eruption site before
solidifying.
Examples
of flood basalt provinces include:
- The Deccan Traps in India: This province is
one of the largest flood basalt regions in the world, covering an area of
approximately 500,000 square kilometers. The Deccan Traps were formed by
volcanic activity around 66 million years ago.
- The Columbia Plateau in the United States:
Located in the Pacific Northwest, this province was formed by multiple
episodes of basaltic lava eruptions between 17 and 6 million years ago. It
covers parts of Washington, Oregon, and Idaho.
5.
Explain the concept of geomagnetism and its role in understanding Earth's
magnetic field. Include the principles of palaeomagnetism and magnetic
reversal.
Answer:
Geomagnetism
refers to the Earth's magnetic field, which is generated by the motion of
molten iron and other materials in the Earth's outer core. This magnetic field
extends from the Earth's core into space and is crucial for protecting the
planet from harmful solar radiation.
Key
principles of geomagnetism include:
- Generation of Earth's
Magnetic Field:
The motion of electrically conductive materials in the Earth's outer core
generates the geomagnetic field. This movement is driven by convection
currents caused by the heat released from the solid inner core and the
Earth's rotation.
- Palaeomagnetism: This field studies the
historical variations in Earth's magnetic field recorded in rocks. When
magma cools and solidifies, ferromagnetic minerals within it align with
the Earth's magnetic field, preserving a record of the field's direction
and strength at that time. This preserved magnetism, known as fossil
magnetism, helps scientists understand past changes in the magnetic field
and plate movements.
- Magnetic Reversal: Over geological
timescales, Earth's magnetic field has reversed its polarity, with the
magnetic north and south poles switching places. These reversals,
occurring every 200,000 to 300,000 years, are recorded in the geological
strata and help in studying the history of geomagnetic field changes. The
reversals are caused by changes in the convection currents in the outer
core, which affect the magnetic field generation.
Understanding
geomagnetism and palaeomagnetism helps scientists study the Earth's past
magnetic field behavior, plate tectonics, and the dynamic processes occurring
within the Earth's interior.
1)
With reference to Types of volcanoes, consider the following statements:
- Composite volcanoes often result in explosive eruptions
- The Caldera Volcanoes are the most explosive of the earth’s volcanoes.
- The shield volcanoes are the largest of all the volcanoes on the earth.
Which of the statements given above is/are correct?
(a)1 only
(b)1 and 3 only
(c)2 and 3 only
(d)1, 2 and 3
2)
With reference to Volcanic landforms, which of the following are intrusive structures?
- Batholiths.
- Strato-volcano.
- Dykes.
- Sills.
- Cinder cones.
Select the code for the correct answer:
(a)1, 2 and 4
(b)1, 2, 3 and 5
(c)1, 3 and 4
(d)2, 3 and 5
3)
Consider the following statements:
- Palaeomagnetism is the historical study of the radiation of Earth.
- Palaeomagnetism implies that the magnetic field of the Earth has remained constant throughout the geological time scale.
Which of the statements given above is/are correct?
(a)Only 1
(b)Only 2
(c)Both 1 and 2
(d)Neither 1 nor 2
4)
Consider the following statements with regard to the phenomenon of Aurora:
- Auroras are produced in the upper atmosphere when the magnetosphere is sufficiently disturbed by solar winds.
- They are more prominent over the equator as opposed to the poles.
- The phenomenon in the Southern Hemisphere is referred to as the Aurora Borealis.
Which of the statements given above is/are correct?
(a)1 only
(b)1 and 2 only
(c)All of the above
(d)1 and 3 only
5)
Which of the following are the highest of all the volcanic cones and are formed due to the accumulation of different layers of various volcanic materials due to the deposition of alternate layers of lava and fragmental materials?
(a)Cinder Cone
(b)Caldera
(c)Composite cone
(d)Parasite cone
6)
Consider the following statements regarding the causes of Geomagnetism:
- It is caused by the electric current movement of molten metals in motion in the outer core creating a magnetic field.
- It is caused due to the creation of a convection current that moves circularly in the outer core.
Which of the statements given above is/are correct?
(a)1 only
(b)2 only
(c)Both 1 and 2
(d)Neither 1 nor 2
7)
Consider the following statements.
1. Hot Springs and Geysers are forms of intrusive volcanic landforms.
2. Hot springs are water that sinks deep enough beneath the surface to be heated by a hot spot or a magma chamber.
3. Geysers are hot water and superheated steam which ejects continuously.
How many of the above statements is/are correct?
(a)Only one
(b)Only two
(c)All three
(d)None
8)
The term "Polar Wandering" is associated with which of the following phenomena?
(a)Migration of norther polar star around the Earth.
(b)Movement of the Earthquakes from the north pole to the south pole.
(c)Migration of the magnetic poles over the surface of Earth through geologic time.
(d)Periodic variation of the axial tilt of the Earth towards the sun.
9)
Discuss the concept of geomagnetism and also highlight the causes that make earth to behave as magnet . (150 words/10 marks)
10)
What due you understand by Paleomagnetism and Polar wandering?(10 Marks/150 Words)
Answers
1) d
2) c
3) d
4) a
5) c
6) c
7) a
8) c
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