Overview
Previous Year UPSC-CSE Questions By the end you will be able to draft model answers for the following UPSC questions. Each question carries a collapsible framework showing how to approach it in the exam.
- UPSC Prelims 2019 GS-IWhich of the following statements are correct about the deposits of 'methane hydrate'?
- Global warming might trigger the release of methane gas from these deposits.
- Large deposits of 'methane hydrate' are found in Arctic Tundra and under the seafloor.
- Methane in atmosphere oxidizes to carbon dioxide after a decade or two.
Select the correct answer using the code given below:
How to approach this Prelims question
Approach: Check each statement against the occurrence, climate behaviour and atmospheric chemistry of methane hydrate.
Trap to watch: All three are correct; do not drop statement 3 (methane's short atmospheric lifetime is real).
Key facts to recall:
- Warming can dissociate hydrates and release methane (clathrate-gun feedback).
- Deposits occur in Arctic tundra/permafrost and in ocean-floor sediments.
- Atmospheric methane oxidises to carbon dioxide within a decade or two.
Answer signal: All three statements are correct, so the answer is (d) 1, 2 and 3.
A natural gas hydrate (methane hydrate, or fire ice) is a solid in which methane is trapped inside a cage of water ice, stable only at high pressure and low temperature; vast deposits occur in ocean-floor sediments and Arctic permafrost, including India's Krishna-Godavari basin, making hydrates a possible future fuel that is hard to extract and a methane climate hazard.
What natural gas hydrates are
Fire ice: methane trapped in water
A natural gas hydrate, or methane hydrate, is a solid in which a large amount of methane is trapped inside a crystal cage of water, forming a substance that looks like ordinary ice. Because the trapped methane burns when the solid is lit, it is popularly called fire ice or burning ice.
The hydrate is not a chemical fuel in its own right; it is a way of storing methane gas in a frozen, concentrated form. A single block of hydrate packs a great deal of natural gas into a small volume, which is what makes it so interesting as a possible fuel.
How they form: high pressure and low temperature
Methane hydrate forms only where methane and water meet at high pressure and low temperature. For example, at about 4 degrees Celsius the hydrate is stable above a pressure of roughly 50 atmospheres, the conditions found at around 500 metres of sea depth.
These narrow conditions define a stability zone in the sediments. If the pressure falls or the temperature rises, the cage breaks down and the methane is released as gas, a property that is central both to extracting the fuel and to the climate risk it carries.
Where natural gas hydrates occur
Sea-floor sediments and Arctic permafrost
Gas hydrates form in just two kinds of setting. The largest deposits lie in the sediments of the deep ocean floor, along continental margins, typically around 1,100 metres below the sea surface where the pressure is high and the water is cold.
The second setting is beneath the Arctic permafrost, in places such as Siberia and Alaska, in sandstone and siltstone beds at depths of less than 800 metres. So the headline fact for the exam is that large deposits occur both in the Arctic tundra and under the seafloor.
A vast but locked energy resource
The scale of the resource is enormous. Global estimates put the carbon locked in gas hydrates at roughly 500 to 2,500 gigatonnes, far more than the carbon in all other conventional natural gas sources, which is estimated at around 230 gigatonnes.
That is why hydrates are described as the world's largest untapped store of fossil energy. The catch is in the word untapped: the methane is real and abundant, but it is locked in a frozen, scattered form that is very hard to bring up economically.
Natural gas hydrates in India
India's deposits: the Krishna-Godavari basin
India sits among the regions with significant gas-hydrate potential, in the sediments off its long coastline. The deposits are best mapped in the Krishna-Godavari basin, in the Bay of Bengal off Andhra Pradesh, which holds the country's confirmed gas-hydrate accumulations.
Other offshore sedimentary basins, including the Mahanadi, the Andaman, the Cauvery and the basins off the west coast, are prospective ground for further hydrate exploration. The richest and best-studied Indian deposits, however, remain those of the Krishna-Godavari basin.
India's energy stake and exploration
For India, which imports most of its oil and gas, a domestic store of methane on this scale is a powerful strategic prize. A national gas-hydrate exploration effort has surveyed and drilled in the offshore basins to map the deposits and test how they might one day be produced.
So far, though, that prize is potential rather than real. No country yet produces gas hydrates commercially, and for India the resource remains a long-term frontier: a possible future contribution to energy security that depends on solving the hard problem of extraction.
The promise and the extraction challenge
Why gas hydrates are a tantalising fuel
The appeal is simple arithmetic. Hydrates hold more methane than all conventional gas fields combined, and methane is a relatively clean-burning fossil fuel, so tapping even a fraction could ease the energy worries of import-dependent countries.
If the gas could be produced safely and cheaply, hydrates might extend the world's natural-gas supply for many decades and give nations such as India a large home-grown fuel. That single conditional, if it could be produced, is where the difficulty lies.
Why they are so hard to extract
Producing gas from a hydrate means deliberately breaking the cage to release the methane, which is far harder than drilling a normal gas well. The main approaches all aim to push the deposit out of its stability zone.
| Method | How it works |
|---|---|
| Depressurisation | Lowering the pressure in the deposit so the hydrate breaks down |
| Thermal stimulation | Warming the deposit to release the trapped methane |
| Inhibitor injection | Adding chemicals that destabilise the hydrate cage |
Each method is technically demanding, costly and slow, and breaking down hydrates in sea-floor sediments can trigger slope failures and submarine landslides. These barriers are why no commercial production exists, and why hydrates remain a fuel of the future rather than the present.
The climate dimension
A potent greenhouse gas and a climate feedback
Methane is a powerful greenhouse gas, with around 81 times the warming effect of carbon dioxide over a twenty-year period. So the methane locked in hydrates is not only a fuel but a climate hazard if it escapes to the atmosphere uncombusted.
This creates a dangerous feedback: global warming can heat the sediments and trigger the release of methane from the deposits, and that methane causes further warming, the idea known as the clathrate gun hypothesis. The one mercy is that atmospheric methane oxidises to carbon dioxide within a decade or two, so its intense warming effect is relatively short-lived.
A double-edged resource and a submarine hazard
Gas hydrates are therefore double-edged. The same deposits that promise energy are a store of greenhouse gas that warming could unlock, and disturbing them, whether by drilling or by a warming ocean, can destabilise the sea floor and cause underwater landslides.
This is the dilemma for policy. Exploiting hydrates means producing yet another fossil fuel at a time of climate transition, so any future use has to be weighed against the warming and hazard risks, not just the energy reward.
How natural gas hydrates appear in the UPSC exam
Gas hydrates in Environment and Science
Gas hydrates are a favourite of the Environment and Science and Technology sections, usually as a multi-statement Prelims question. The high-yield points are few and clear.
- A gas hydrate is methane trapped in a cage of water ice (fire ice), stable at high pressure and low temperature.
- Large deposits occur in ocean-floor sediments and beneath the Arctic permafrost.
- Global warming can release methane from these deposits, a self-reinforcing climate feedback.
- In India, the Krishna-Godavari basin in the Bay of Bengal holds the confirmed deposits.
A strong answer treats hydrates as both a possible energy source and a climate risk, covers their occurrence and the extraction problem, and adds the Indian Krishna-Godavari angle, exactly the balance this article develops.
Prelims MCQ practice
Each question below tests one specific concept on the topic. Click to reveal the answer and a full option-wise explanation.
Q1. 'Fire ice' or 'burning ice' refers to:
- dry ice (solid carbon dioxide)
- methane hydrate, methane trapped in a cage of water ice
- frozen petroleum
- glacial ice with trapped air
Show answer and explanation
Answer: methane hydrate, methane trapped in a cage of water ice
Explanation.
Fire ice is methane hydrate: methane trapped in a crystal cage of water that looks like ice but burns when lit. Dry ice is solid carbon dioxide. Hence (b).
Q2. Methane hydrates are stable mainly under conditions of:
- high temperature and low pressure
- high pressure and low temperature
- low pressure and low temperature
- high temperature and high pressure
Show answer and explanation
Answer: high pressure and low temperature
Explanation.
Methane hydrate forms and remains stable only at high pressure and low temperature, such as deep sea-floor sediments and beneath permafrost. Hence (b).
Q3. With reference to natural gas hydrates in India, consider the following statements:
- The Krishna-Godavari basin in the Bay of Bengal holds confirmed gas-hydrate deposits.
- India currently produces gas from hydrates on a commercial scale.
- India imports a large share of its oil and natural gas.
Which of the statements given above is/are correct?
- 1 and 3 only
- 2 and 3 only
- 1 and 2 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 3 only
Explanation.
Statements 1 and 3 are correct. Statement 2 is wrong: no country, including India, yet produces gas hydrates commercially. Hence 1 and 3 only.
Q4. Which of the following is NOT a recognised method of extracting gas from hydrates?
- depressurisation
- thermal stimulation
- inhibitor injection
- hydraulic fracturing of coal seams
Show answer and explanation
Answer: hydraulic fracturing of coal seams
Explanation.
Gas hydrates are produced by depressurisation, thermal stimulation or inhibitor injection, all of which break down the hydrate cage. Hydraulic fracturing of coal seams is a different (coal-bed methane) technique. Hence (d).
Q5. Why are gas hydrates considered a climate concern?
- they release sulphur dioxide when burnt
- warming can release methane, a potent greenhouse gas, in a self-reinforcing feedback
- they deplete the ozone layer
- they acidify the oceans directly
Show answer and explanation
Answer: warming can release methane, a potent greenhouse gas, in a self-reinforcing feedback
Explanation.
Warming can dissociate hydrates and release methane, a potent greenhouse gas, which causes further warming, the clathrate-gun feedback. Hence (b).
Q6. Consider the following statements about methane:
- Methane is a more potent greenhouse gas than carbon dioxide over a twenty-year period.
- Atmospheric methane oxidises to carbon dioxide within a decade or two.
- Methane hydrates are found only in tropical deserts.
Which of the statements given above is/are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 2 only
Explanation.
Statements 1 and 2 are correct. Statement 3 is wrong: hydrates occur in ocean-floor sediments and Arctic permafrost, not tropical deserts. Hence 1 and 2 only.
Sources and Further Reading
Editorial Disclaimer
This article explains natural gas hydrates for UPSC preparation, drawing on standard earth-science sources. Figures and conditions reflect the cited authorities.
