Type: Prelims Only

At least 70 people died in lightning strikes across Uttar Pradesh, Madhya Pradesh and Rajasthan.

What is lightning?

• Scientifically, lightning is a rapid and massive discharge of electricity in the atmosphere some of which is directed towards earth.
• The discharges are generated in giant moisture-bearing clouds that are 10-12 km tall.
• The base of these clouds typically lie within 1-2 km of the Earth’s surface, while the top is 12-13 km away.
• Temperatures in the top of these clouds are in the range of –35° to –45°C.

Its formation

• As water vapour moves upward in the cloud, the falling temperature causes it to condense.
• As they move to temperatures below 0°C, the water droplets change into small ice crystals.
• They continue to move up, gathering mass until they are so heavy that they start to fall to Earth.
• This leads to a system in which, simultaneously, smaller ice crystals are moving up and bigger crystals are coming down.
• Collisions follow and trigger the release of electrons, a process that is very similar to the generation of sparks of electricity.
• As the moving free electrons cause more collisions and more electrons, a chain reaction ensues.
• This process results in a situation in which the top layer of the cloud gets positively charged, while the middle layer is negatively charged.
• The electrical potential difference between the two layers is huge, of the order of a billion to 10 billion volts.
• In very little time, a massive current, of the order of 100,000 to a million amperes, starts to flow between the layers.

Types of lightning

• Broadly, there are three forms of lightning:

1. Inter-cloud
2. Intra-cloud
3. Cloud-to-ground

• It is the cloud-to-ground form of lightning that kills humans, as well as animals and livestock, and can substantially damage property.
• While the Earth is a good conductor of electricity, it is electrically neutral.
• However, in comparison to the middle layer of the cloud, it becomes positively charged.
• As a result, about 15%-20% of the current gets directed towards the Earth as well.
• It is this flow of current that results in damage to life and property on Earth.

How intensely does it strike?

• A typical lightning flash is about 300 million volts and 30,000 amps.
• To put it in perspective, household current is 120 volts and 15 amps.
• A flash of lightning is enough to light a 100-watt incandescent bulb for about three months.

Why does lightning kill so many people in India?

• The reason for the high number of deaths is due to people being caught unawares and more than 70% of fatalities happened due to people standing under isolated tall trees.
• About 25 per cent of the people were struck in the open.
• Also, lightning is the direct promulgation of climate change extremities.

Mitigating lightning incidents

• Lightning is not classified as a natural disaster in India.
• But recent efforts have resulted in the setting up of an early warning system that is already saving many lives.
• More than 96% of lightning deaths happen in rural areas.
• As such, most of the mitigation and public awareness programmes need to focus on these communities.
• Lightning protection devices are fairly unsophisticated and low-cost. Yet, their deployment in the rural areas, as of now, is extremely low.
• States are being encouraged to prepare and implement lightning action plans, on the lines of heat action plans.
• An international centre for excellence on lightning research to boost detection and early warning systems is also in the process of being set up.

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Most of us may not know the small desert situated in the state of Tamil Nadu. It consists of red sand dunes and is confined to the Thoothukudi district.

Theri Desert

• The red dunes are called theri in Tamil.
• They consist of sediments dating back to the Quaternary Period and are made of marine deposits.
• They have very low water and nutrient retention capacity.
• The dunes are susceptible to aerodynamic lift.
• This is the push that lets something move up. It is the force that is the opposite of weight.

Mineral composition of Theris

• The analysis of the red sand dunes reveal the presence of heavy and light minerals.
• These include Ilmenite, Magnetit, Rutile, Garnet, Zircon, Diopside, Tourmaline, Hematite, Goethite, Kyanite, Quartz, Feldspar, Biotite.
• The iron-rich heavy minerals like ilmenite, magnetite, garnet, hypersthene and rutile present in the soil had undergone leaching by surface water.
• They were then oxidised because of the favourable semi-arid climatic conditions.

How did they form?

• Theris appear as gentle, undulating terrain.
• The lithology of the area shows that the area might have been a paleo (ancient) coast in the past.
• The presence of limestone in many places indicates marine transgression.
• The present-day theris might have been formed by the confinement of beach sand locally, after regression of the sea.
• When high velocity winds from the Western Ghats blew east, they induced migration of sand grains and accumulation of dunes.

Another story of their formation

• Another view is that these are geological formations that appeared in a period of a few hundred years.
• The red sand is brought from the surface of a broad belt of red loam in the plains of the Nanguneri region (about 57 kilometres) by south west monsoon winds during May-September.
• The winds after draining the moisture behind the Mahendragiri hill and the Aralvaimozhi gap of the Western Ghats become dry and strike the plains in the foothills, where vegetation is sparse.
• Deforestation and the absence of vegetative cover in the Aralvaimozhi gap and the Nanguneri plains are considered to be the major causes of wind erosion.

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