Class 11 Geography: Water (Hydrosphere)
A. Multiple Choice Questions (MCQs) - 1 Mark Each (Total: 15 Marks)
Approximately what percentage of the Earth's surface is covered by water?
a) 51%
b) 61%
c) 71%
d) 81%
Answer: c) 71%
Hint: Think about the commonly cited proportion of Earth's surface that is ocean.
Rationale: About 71% of Earth's surface is covered by water, predominantly oceans.
The process by which liquid water changes into water vapor and rises into the atmosphere is called:
a) Condensation
b) Precipitation
c) Evaporation
d) Infiltration
Answer: c) Evaporation
Hint: This is the initial step in the water cycle where water moves from surface to atmosphere.
Rationale: Evaporation is the process where liquid water turns into a gas (water vapor). Condensation is the opposite, precipitation is water falling from clouds, and infiltration is water soaking into the ground.
Which of the following ocean relief features represents the submerged extension of the continent?
a) Abyssal plain
b) Oceanic trench
c) Continental shelf
d) Mid-oceanic ridge
Answer: c) Continental shelf
Hint: This is the shallowest part of the ocean near land.
Rationale: The continental shelf is the gently sloping, submerged extension of the continental landmass, typically shallow and rich in marine life.
The deepest parts of the ocean, often associated with convergent plate boundaries, are:
a) Guyots
b) Seamounts
c) Abyssal plains
d) Oceanic trenches
Answer: d) Oceanic trenches
Hint: Think about the features formed by subduction zones.
Rationale: Oceanic trenches are long, narrow, and very deep depressions on the ocean floor, typically formed at convergent plate boundaries where one plate subducts beneath another.
What is the primary factor influencing the formation and direction of most ocean currents?
a) Gravitational pull of the Moon
b) Salinity differences
c) Prevailing winds
d) Volcanic activity
Answer: c) Prevailing winds
Hint: Consider the force that directly pushes surface water.
Rationale: While salinity differences and Coriolis effect also play a role, prevailing winds are the primary driving force behind most major surface ocean currents, transferring energy from the atmosphere to the ocean.
High tides are generally caused by the gravitational pull of:
a) The Sun only
b) The Moon only
c) Both the Sun and the Moon
d) Earth's rotation
Answer: c) Both the Sun and the Moon
Hint: Consider the celestial bodies closest to Earth that exert gravitational force.
Rationale: Tides are primarily caused by the gravitational pull of the Moon and, to a lesser extent, the Sun, which exert differential forces on the Earth's water bodies.
Which of the following is a cold ocean current?
a) Gulf Stream
b) Kuroshio Current
c) Labrador Current
d) North Atlantic Drift
Answer: c) Labrador Current
Hint: This current flows from high latitudes towards lower latitudes.
Rationale: The Labrador Current is a cold ocean current flowing from the Arctic Ocean south along the coast of Labrador and Newfoundland. The others listed are warm currents.
The average salinity of ocean water is approximately:
a) 25 parts per thousand (‰)
b) 30 parts per thousand (‰)
c) 35 parts per thousand (‰)
d) 40 parts per thousand (‰)
Answer: c) 35 parts per thousand (‰)
Hint: This is a standard global average.
Rationale: The average salinity of ocean water is about 35 parts per thousand (‰), meaning 35 grams of dissolved salts per 1000 grams of water.
Which of the following is NOT a component of the hydrological cycle?
a) Transpiration
b) Sublimation
c) Photosynthesis
d) Runoff
Answer: c) Photosynthesis
Hint: This is a biological process, not directly a water phase change or movement.
Rationale: Photosynthesis is the process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. Transpiration, sublimation (ice to vapor), and runoff are all integral parts of the hydrological (water) cycle.
What is a 'Spring Tide'?
a) A tide that occurs only in spring season.
b) A very high tide that occurs when the Sun, Moon, and Earth are aligned.
c) A tide that occurs during quarter moon phases.
d) A tide caused by underground springs.
Answer: b) A very high tide that occurs when the Sun, Moon, and Earth are aligned.
Hint: Think about the combined gravitational pull of the Moon and Sun.
Rationale: Spring tides are exceptionally high tides (and correspondingly low low tides) that occur when the Sun, Moon, and Earth are aligned (during new moon and full moon phases), resulting in their combined gravitational pull.
The vast, flat, deep ocean floor areas are known as:
a) Continental slopes
b) Abyssal plains
c) Oceanic islands
d) Submarine canyons
Answer: b) Abyssal plains
Hint: These are the plains of the deep sea.
Rationale: Abyssal plains are large, flat, or gently sloping areas of the deep ocean floor, usually found at depths between 3,000 and 6,000 meters.
The highest salinity in ocean water is generally observed in:
a) Equatorial regions
b) Polar regions
c) Subtropical regions (around 20°-30° latitude)
d) Temperate regions
Answer: c) Subtropical regions (around 20°-30° latitude)
Hint: Consider areas with high evaporation and low precipitation.
Rationale: Subtropical regions typically exhibit the highest salinity due to high rates of evaporation, relatively low precipitation, and limited freshwater input from rivers. Equatorial regions have high precipitation, and polar regions have melting ice, both leading to lower salinity.
What phenomenon is primarily responsible for the circular movement of ocean currents in major ocean basins (gyres)?
a) Tides
b) Tsunamis
c) Coriolis force
d) Submarine volcanoes
Answer: c) Coriolis force
Hint: This force affects all large-scale moving objects on Earth.
Rationale: The Coriolis force, due to Earth's rotation, deflects moving ocean water, causing the large-scale, circular patterns of ocean currents known as gyres.
The term 'Thermohaline Circulation' refers to ocean currents driven by differences in:
a) Wind speed and direction
b) Temperature and salinity
c) Lunar and solar gravity
d) Ocean depth and width
Answer: b) Temperature and salinity
Hint: Break down the word: 'thermo' and 'haline'.
Rationale: Thermohaline circulation, also known as the 'great ocean conveyor belt', is a global-scale ocean current system driven by differences in water density, which is primarily controlled by temperature (thermo) and salinity (haline).
Most of the freshwater on Earth is stored in:
a) Lakes and rivers
b) Groundwater
c) Ice caps and glaciers
d) The atmosphere
Answer: c) Ice caps and glaciers
Hint: Consider the largest frozen reservoirs of water.
Rationale: While lakes, rivers, and groundwater are important, the vast majority (about 68.7%) of Earth's freshwater is locked up in ice caps and glaciers.
B. Short Answer Questions (2-3 Marks Each) - (Total: 20-30 Marks)
List the major components of the hydrological cycle.
Answer: The major components of the hydrological cycle are: Evaporation, Condensation, Precipitation, Runoff, Infiltration, Transpiration, and Storage (e.g., in oceans, glaciers, groundwater).
Explain why coastal areas often experience more moderate temperatures than inland areas.
Answer: Coastal areas experience more moderate temperatures (maritime or equable climate) because water has a higher specific heat capacity than land. This means water heats up and cools down much slower than land. Oceans act as giant heat reservoirs, absorbing heat during summer and releasing it during winter, thus moderating the temperature of adjacent landmasses.
Differentiate between 'Spring Tides' and 'Neap Tides'.
Answer: Spring Tides are exceptionally high high tides and very low low tides that occur when the Sun, Moon, and Earth are aligned in a straight line (during new moon and full moon phases). Their gravitational pulls combine to create the strongest tidal forces. Neap Tides are unusually low high tides and high low tides that occur when the Sun and Moon are at right angles to each other relative to Earth (during quarter moon phases). Their gravitational pulls partially cancel each other out, resulting in weaker tidal forces.
Briefly describe the significance of oceanic trenches.
Answer: Oceanic trenches are significant because they represent the deepest parts of the ocean floor and are crucial to understanding plate tectonics. They are formed at convergent plate boundaries where one oceanic plate subducts beneath another plate. They are zones of intense geological activity, including frequent and powerful earthquakes, and are often associated with volcanic island arcs or volcanic mountain ranges on the overriding plate.
How does salinity affect the density of ocean water? What is its role in ocean circulation?
Answer: Increased salinity increases the density of ocean water. Denser water tends to sink. This density difference, driven by variations in temperature (thermo) and salinity (haline), is a primary driver of Thermohaline Circulation (or the 'great ocean conveyor belt'). This global system of deep ocean currents transports heat and nutrients around the world, playing a vital role in global climate regulation.
List three main types of precipitation.
Answer: The three main types of precipitation are:
Convectional Rainfall: Due to localized heating and rising air.
Orographic Rainfall: Due to moist air forced to rise over mountains.
Cyclonic (or Frontal) Rainfall: Associated with cyclones or fronts where warm and cold air masses meet.
Explain the 'Coriolis Force' and its effect on ocean currents.
Answer: The Coriolis Force is an apparent force resulting from the Earth's rotation. It deflects moving objects (including ocean currents) to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This force is crucial in influencing the direction of ocean currents, leading to the formation of large circular patterns called gyres in the major ocean basins.
What are 'Seamounts' and 'Guyots'?
Answer: Both Seamounts and Guyots are submarine mountains that rise from the ocean floor but do not reach the surface. A seamount is a conical-shaped undersea mountain. A guyot (or tablemount) is a seamount with a flat top, which indicates that it once rose above sea level and was truncated by wave action before subsiding below the surface. They are typically volcanic in origin.
Why is fresh water a scarce resource despite Earth being a 'water planet'?
Answer: Despite Earth being a 'water planet' with 71% coverage, about 97% of this water is saline (oceans and seas) and unsuitable for direct human consumption, agriculture, or most industrial uses. Of the remaining 3% freshwater, roughly 68.7% is locked up in ice caps and glaciers, and about 30% is groundwater. Only a tiny fraction (less than 1%) is readily available as surface water in lakes, rivers, and the atmosphere, making it a scarce and vulnerable resource for human use.
Briefly describe two methods of water conservation.
Answer: Two methods of water conservation are:
Rainwater Harvesting: Collecting and storing rainwater (from rooftops, ground surfaces) for future use (e.g., recharging groundwater, direct use for irrigation, domestic purposes). This reduces reliance on conventional water sources and prevents runoff.
Efficient Irrigation Techniques: Implementing techniques like drip irrigation or sprinkler systems instead of traditional flood irrigation. These methods deliver water directly to plant roots, significantly reducing water wastage due to evaporation or runoff and conserving water in agriculture.
C. Long Answer Questions (5-6 Marks Each) - (Total: 10-12 Marks)
1-Explain the relief features of the ocean floor. Discuss how these features are formed and their significance in understanding Earth's geology.
Answer:
The ocean floor is not a flat, featureless plain but possesses diverse and complex relief features, just like continents. These features are primarily formed by tectonic processes and sedimentation. Understanding them is crucial for comprehending Earth's geology and plate tectonics.
Major Relief Features of the Ocean Floor:
Continental Shelf:
Description: The gently sloping, submerged extension of the continent. It's the shallowest part of the ocean, typically less than 200 meters deep.
Formation: Formed by the deposition of sediments brought by rivers and waves from the land, and also by changes in sea level.
Significance: Biologically very productive, rich in marine life, important fishing grounds, and often contains significant oil and gas reserves.
Continental Slope:
Description: A steep slope that descends from the edge of the continental shelf to the deep ocean floor. Its gradient is much steeper than the shelf.
Formation: Represents the true edge of the continental crust where it transitions to oceanic crust. Often dissected by submarine canyons.
Significance: Marks the boundary between continental and oceanic crust. Submarine canyons here channel sediments to the deep sea.
Continental Rise:
Description: A gently sloping area at the base of the continental slope, leading to the abyssal plain. It's composed of accumulated sediments that have slid down the slope.
Formation: Formed by the deposition of turbidites (sediments carried by turbidity currents) and other material at the foot of the continental slope.
Significance: A depositional environment marking the transition from the continental margin to the deep ocean basin.
Deep Sea Plain (Abyssal Plain):
Description: Vast, flat, or gently undulating plains found at depths typically between 3,000 to 6,000 meters. They cover a significant portion of the ocean floor.
Formation: Formed by the accumulation of fine sediments (pelagic oozes and clays) transported from land or settled from the water column over millions of years, burying the underlying irregular topography.
Significance: Considered the flattest regions on Earth, providing insights into slow geological processes and deep-sea ecosystems.
Oceanic Trenches:
Description: Long, narrow, and very deep (often > 6,000m) depressions in the ocean floor, typically arc-shaped. The Mariana Trench is the deepest.
Formation: Formed at convergent plate boundaries where one oceanic plate subducts (slides) beneath another oceanic plate or a continental plate. This process creates a deep down-folding of the ocean floor.
Significance: Sites of intense geological activity, frequent strong earthquakes, and active volcanism. They are critical evidence for plate tectonics and the recycling of oceanic crust.
Mid-Oceanic Ridges:
Description: Submerged mountain ranges that run through the center of all major ocean basins, forming the longest mountain chain on Earth (approx. 65,000 km). They have a central rift valley.
Formation: Formed at divergent plate boundaries where tectonic plates are pulling apart. Magma rises from the mantle to fill the gap, solidifying to create new oceanic crust (seafloor spreading).
Significance: Primary sites of new oceanic crust formation, volcanic activity, and shallow earthquakes. Crucial evidence for seafloor spreading and plate tectonics.
Seamounts and Guyots:
Description: Isolated submarine mountains of volcanic origin. Seamounts are conical-shaped; Guyots are flat-topped (tablemounts).
Formation: Formed from underwater volcanic eruptions. Guyots get their flat tops from wave erosion when they were once above sea level, followed by subsequent subsidence.
Significance: Provide insights into past sea levels and volcanic activity in the ocean basins.
2-Discuss the causes and consequences of ocean currents. Explain how they influence global climate and marine life.
Answer:
Ocean currents are continuous, directed movements of ocean water generated by several forces acting upon the water. They can be classified as surface currents (driven by wind) or deep ocean currents (driven by density differences).
Causes of Ocean Currents:
Prevailing Winds (Primary Driver for Surface Currents): Persistent global wind systems (e.g., Trade Winds, Westerlies) exert friction on the ocean surface, pushing the water and initiating surface current movements.
Coriolis Force: Due to Earth's rotation, the Coriolis force deflects ocean currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, causing them to form large circular patterns called gyres in major ocean basins.
Temperature Differences (Thermo): Water expands when heated and contracts when cooled. Warmer water is less dense and tends to rise, while colder water is denser and tends to sink. This creates convection currents.
Salinity Differences (Haline): Salinity increases the density of water. Water with higher salinity is denser and sinks, while less saline water is lighter and tends to float.
Density Differences (Thermohaline Circulation): The combined effect of temperature and salinity creates density gradients, driving deep ocean currents. Cold, saline water formed in polar regions sinks and flows along the ocean floor towards the equator, forming the Great Ocean Conveyor Belt.
Landmass Configuration: Continents act as barriers, deflecting and channeling ocean currents, influencing their path and forming distinct current systems.
Gravity: Differences in water level (due to density or piling up of water) create pressure gradients, causing water to flow from higher to lower levels.
Consequences/Impacts of Ocean Currents:
Influence on Global Climate:
Heat Distribution: Ocean currents play a crucial role in redistributing heat from the tropics towards the poles, and cold water from poles towards the equator. This moderates global temperatures.
Warm Currents: Bring warm, moist air to coastal regions, making them warmer and often wetter than their latitude would suggest. Example: The Gulf Stream and North Atlantic Drift keep Western Europe's climate mild and navigable during winter.
Cold Currents: Bring cold, dry air, leading to cooler temperatures and often creating deserts on adjacent landmasses. Example: The cold Peru (Humboldt) Current contributes to the aridity of the Atacama Desert in South America.
Fog Formation: Where warm and cold currents meet, dense fog often forms due to the rapid cooling of moist air over the cold water. Example: The Grand Banks off Newfoundland, where the warm Gulf Stream meets the cold Labrador Current.
Influence on Marine Life and Fishing Grounds:
Upwelling Zones: Cold ocean currents often bring nutrient-rich waters from the deep ocean to the surface (upwelling). These areas are highly productive, supporting abundant marine life and leading to some of the world's richest fishing grounds. Example: The Peru Current sustains rich fisheries off the coast of South America.
Convergence Zones: Areas where warm and cold currents meet are often biologically productive due to the mixing of waters and nutrients.
Habitat Creation: Currents transport larvae and plankton, influencing the distribution and migration patterns of marine species.
Navigation and Shipping: Knowing the direction and speed of ocean currents can significantly impact shipping routes, reducing travel time and fuel consumption (e.g., sailing with a favorable current).
Pollutant Dispersion: Ocean currents also play a role in dispersing pollutants (like oil spills) across vast areas, making cleanup efforts challenging.
In summary, ocean currents are a vital component of Earth's climate system and marine ecosystems, demonstrating the interconnectedness of the hydrosphere with the atmosphere and biosphere.
