Water & Weather Phenomena
Almost every dramatic thing water and air do comes down to a few ideas: differences in pressure and temperature, the spin of the Earth, gravity, and the way water carries and releases heat.
Start with the whirlpool and the tides, then work outward to storms, ice and the strange behaviour of soaked sand. Each page opens with a written explanation. You can also request a visual lesson using available credits or plan allowance and your selected options.
Start here
How does a whirlpool form?
A whirlpool works as a rotating mass of water that forms when opposing currents or a draining flow set the water spinning. As water rushes toward a low point or where currents meet, it swirls faster and faster, sometimes pulling things toward its center.
How do tides work?
Tides work because the Moon's gravity pulls harder on the side of Earth facing it than on the far side, stretching the oceans into two bulges. As Earth rotates beneath those bulges, each coast passes through them — giving most places two high tides and two low tides a day.
How does a dam work?
A dam works by blocking a river to hold back a large reservoir of water, using the wall's strength to resist the immense pressure. Many dams also generate electricity by letting the stored water rush down through turbines on its way out.
Every explainer in this guide · 76
How does quicksand work?
Quicksand works when ordinary sand becomes saturated with water, so it can no longer support weight. The water separates the grains, turning solid-looking ground into a soupy mix you sink into — though it's rarely deep enough to swallow you whole.
How does the water cycle work?
The water cycle works as a continuous loop powered by the Sun and gravity: water evaporates from oceans and land, rises and condenses into clouds, falls as precipitation, and flows back to the sea to start again.
How does evaporation work?
Evaporation happens when liquid turns into gas at its surface. The fastest-moving molecules near the surface gain enough energy to escape into the air — which is why puddles dry up and wet clothes dry, especially when it's warm or breezy.
How does a tornado form?
A tornado forms when a thunderstorm's rising warm air meets winds blowing at different speeds and directions, setting the air spinning. That spin can tighten into a violent, funnel-shaped column stretching from cloud to ground.
How does a hurricane form?
A hurricane forms over warm ocean water, which evaporates and feeds rising, spinning storm clouds. As the moist air rises and condenses, it releases heat that powers ever-stronger winds, building a giant rotating storm with a calm eye at its center.
How does lightning form?
Lightning forms when charges separate inside a storm cloud — light positive charge near the top, heavy negative charge near the bottom. When the difference grows large enough, it overcomes the air's resistance and discharges as a giant spark.
How does thunder work?
Thunder works as the sound of lightning: a bolt heats the air around it so fast that the air explosively expands, creating a shockwave we hear as a boom. Because light travels faster than sound, you see the flash before you hear the thunder.
How does a rainbow form?
A rainbow forms when sunlight passes through raindrops, which bend and split the light into its colors. Each droplet acts like a tiny prism, separating white light into red, orange, yellow, green, blue, and violet, and reflecting them back to your eyes.
How do snowflakes form?
A snowflake forms when water vapor in a cold cloud freezes directly onto a tiny particle, building an ice crystal. As it falls through changing temperature and humidity, it grows six symmetric arms — which is why no two snowflakes are quite alike.
How does snow form?
Snow forms when water vapor high in cold clouds freezes directly into ice crystals, which grow into six-sided snowflakes and fall. Each flake builds its intricate, unique shape as it drifts through air of changing temperature and moisture.
How does a tsunami happen?
A tsunami happens when a large, sudden movement of the seafloor — usually from an undersea earthquake — pushes a huge volume of water upward. That energy spreads as fast, low waves that grow into towering walls of water as they reach shallow coasts.
How does a glacier work?
A glacier works as a slow-moving river of ice, formed where snow piles up faster than it melts and compresses into dense ice over centuries. Its own enormous weight makes it flow downhill, carving valleys and shaping landscapes.
How does an avalanche happen?
An avalanche works when a mass of snow on a slope suddenly breaks loose and slides downhill, often picking up speed and more snow as it goes. It happens when the weight of the snow overcomes the friction holding it in place.
How does a geyser work?
A geyser works when underground water, heated by Earth's deep heat, builds up pressure until it erupts in a jet of steam and water. Water trapped in narrow channels boils, and the sudden pressure release sends it bursting to the surface.
How does erosion work?
Erosion works as the gradual wearing away and carrying off of rock and soil by water, wind, ice, and gravity. Over long timescales it sculpts landscapes — carving canyons, smoothing mountains, and shaping coastlines.
How does a mirage work?
A mirage works when light bends as it passes through air of different temperatures, fooling your eyes. On a hot road, a layer of very hot air near the surface bends light upward, so you see a shimmering 'puddle' that's actually a reflection of the sky.
How does weather forecasting work?
Weather forecasting works by feeding huge amounts of current data — temperature, pressure, wind, humidity from satellites, stations, and balloons — into powerful computer models that simulate how the atmosphere will change over the coming hours and days.
How do the seasons work?
The seasons happen because Earth is tilted on its axis as it orbits the Sun. The tilt means each hemisphere leans toward the Sun for part of the year — getting more direct light and longer days (summer) — and away for the rest (winter).
How does hail form?
Hail forms when strong updrafts in thunderstorms carry raindrops high into freezing air, where they freeze into ice pellets. These pellets grow larger as they collide with supercooled water droplets, eventually falling when they become too heavy for the updraft to support.
How does fog form?
Fog forms when air near the ground cools to its dew point, the temperature at which water vapour condenses into tiny droplets. These droplets stay suspended in the air, reducing visibility to less than one kilometre.
How do clouds form?
Clouds form when water vapour in rising air cools and condenses into tiny droplets or ice crystals around microscopic particles called condensation nuclei. This process happens when air reaches its dew point, the temperature at which it becomes saturated.
How does dew form?
Dew forms when water vapour in the air condenses into liquid droplets on surfaces that have cooled below the air's dew point. This cooling usually happens on clear, calm nights as the ground and objects radiate heat away into space.
How does frost form?
Frost forms when a surface cools below the freezing point of water and water vapour in the air changes directly into ice crystals, skipping the liquid stage. This happens on clear, calm nights when heat radiates away from the ground, chilling objects like grass and car roofs.
How do ocean waves form?
Ocean waves form when wind blows across the water surface, transferring energy that creates ripples and larger waves. The size of a wave depends on wind speed, the distance over which it blows, and how long it blows.
How do rip currents work?
Rip currents are narrow, fast-moving channels of water that flow from the beach out to sea, cutting through the surf zone. They form when waves pile water against the shore and that water finds a weak spot in the sandbar to return offshore.
How does a waterspout form?
A waterspout forms when warm water heats the air above it, making that air rise and spin into a rotating column. Most are fair-weather waterspouts, which are weaker than tornadoes and usually dissipate when they reach land.
How does the monsoon work?
The monsoon is a seasonal reversal of winds that brings heavy rain to tropical regions. It happens because land heats and cools faster than the ocean, creating pressure differences that drive moist air onshore in summer and dry air offshore in winter.
How do floods happen?
Floods happen when water overflows onto normally dry land, often because heavy rain, rapid snowmelt, or storm surges add water faster than rivers, soil, or drainage systems can carry it away. They can also occur when human structures like dams or levees fail, or when coastlines are overwhelmed by ocean water.
How does a drought happen?
A drought develops when an area receives far less rain or snow than usual over months or years, drying out soil and reducing rivers and reservoirs. It worsens when high temperatures and strong evaporation remove remaining moisture, and it ends only when steady rainfall returns.
How do icebergs form?
Icebergs form when snow accumulates on land and compresses into glacial ice, which then flows to the coast and breaks off into the ocean. This calving process creates floating ice masses that drift with currents and gradually melt.
How does a sinkhole form?
A sinkhole forms when underground rock or sediment is dissolved or washed away, creating a void that can no longer support the ground above. The surface then collapses or subsides into the cavity, often suddenly.
How do hot springs work?
Hot springs form when groundwater seeps deep enough to be heated by Earth's geothermal gradient, then rises quickly to the surface through fractures. The water emerges warm or hot because it has absorbed heat from hot rock and sometimes from magma nearby.
How does a river form?
A river forms when rainfall or snowmelt collects in a channel and flows downhill under gravity. As water moves, it erodes the land, deepening and widening the channel into a river.
How does a river delta form?
A river delta forms where a river meets a standing body of water, such as a sea or lake, and its flow slows abruptly, causing it to drop the sediment it carried. This deposited material builds up over time into new land that splits the river into multiple channels called distributaries.
How does a waterfall form?
A waterfall forms where a river flows over a band of hard rock lying above softer rock, and the softer rock erodes faster, creating a steep drop. The falling water and its spray then undercut the hard cap, so the waterfall slowly retreats upstream.
How do thunderstorms form?
Thunderstorms form when warm, moist air rises rapidly in an unstable atmosphere, leading to the growth of towering cumulonimbus clouds. Inside these clouds, collisions between ice particles create electrical charges, causing lightning and thunder.
How does wind form?
Wind forms when air moves from areas of higher pressure to areas of lower pressure. This pressure difference is created by uneven heating of Earth's surface by the Sun, which causes some air to warm, expand, and rise, while cooler, denser air sinks and flows in to replace it.
How does air pressure work?
Air pressure is the force exerted by the weight of air molecules pressing on a surface. It decreases with altitude because fewer molecules are above, and it drives winds from high to low pressure areas.
How does the jet stream work?
The jet stream is a fast, narrow band of wind in the upper atmosphere that forms where warm and cold air masses meet. It flows from west to east because the temperature difference between the poles and the equator creates a pressure gradient that strong winds follow.
How does humidity work?
Humidity measures the amount of water vapor in the air, driven by evaporation and temperature. Warm air holds more vapor than cold air, so when air cools, vapor condenses into dew, clouds, or precipitation.
How does a dust devil form?
A dust devil forms when a patch of ground heats the air above it, making that air rise in a spinning column. As the rising air stretches and tightens, it spins faster and picks up dust and debris from the surface.
How do lakes form?
Lakes form when water collects in a basin that holds it, created by processes like tectonic shifts, glacial carving, or volcanic activity. The basin must have a water source and a way to retain water, allowing the lake to persist.
How does a storm surge happen?
A storm surge happens when a powerful storm's low pressure and strong winds push a wall of ocean water toward the coast, raising sea level far above normal. The surge combines with normal tides and waves, causing severe flooding in low-lying coastal areas.
How does a sea breeze work?
A sea breeze forms when the land heats faster than the sea during the day, causing warm air over land to rise and cooler air from the sea to flow inland. At night, the pattern reverses as the land cools faster, creating a land breeze.
How does freezing rain form?
Freezing rain forms when snow falls through a warm layer of air and melts into raindrops, then falls through a shallow subfreezing layer near the ground without refreezing. The drops become supercooled and freeze on contact with surfaces below 0°C, creating a glaze of ice.
How does a blizzard form?
A blizzard forms when a strong low-pressure system pulls cold air against warm, moist air that rises over it, creating heavy snow, while sustained winds of at least 56 km/h (35 mph) blow the snow into whiteout conditions for at least three hours.
How does a cyclone form?
A cyclone forms when warm ocean water evaporates and the rising moist air condenses, releasing heat that lowers pressure and draws in stronger winds. This self-reinforcing cycle, spun by Earth's rotation, builds a rotating storm system.
How does a heat wave happen?
A heat wave happens when a large, slow-moving high-pressure system parks over a region and traps hot air near the ground for days or weeks. The sinking air compresses and warms, skies stay clear, and the ground keeps heating until temperatures climb far above normal.
How does a rain shadow form?
A rain shadow forms when moist air is forced to rise over a mountain range, cooling and dropping most of its moisture as rain or snow on the windward slopes. The now-dry air descends on the far side, warming and holding more moisture, so the leeward side receives far less precipitation.
How does acid rain form?
Acid rain forms when sulfur dioxide and nitrogen oxides from burning fossil fuels react in the atmosphere to produce sulfuric and nitric acids, which then fall to the ground in rain, snow, or dust. These pollutants can travel hundreds of kilometres, so the pollution that causes acid rain often originates far from where it lands.
How does smog form?
Smog forms when sunlight and heat react with pollutants like nitrogen oxides and volatile organic compounds, creating a brown haze. The word blends 'smoke' and 'fog', and it can be either sulfurous or photochemical.
How does a dust storm form?
A dust storm forms when strong, turbulent winds lift loose, dry soil particles from bare ground into the air, creating a dense, moving wall of dust. This happens most often in arid regions after drought or poor land management has left the surface unprotected by vegetation.
How does a wildfire spread?
A wildfire spreads by heating and igniting nearby fuel, then moving via three main mechanisms: direct flame contact, radiant heat, and burning embers carried by wind. The fire's spread rate depends on fuel type, moisture, wind, and terrain slope.
How does a double rainbow form?
A double rainbow forms when sunlight is reflected twice inside the same raindrop before it exits, sending light back at a higher angle than the primary bow. The second reflection reverses the colour order and spreads the light more thinly, which is why the secondary arc looks fainter.
How does a rogue wave form?
A rogue wave forms when separate wave groups travelling at different speeds and directions briefly overlap and align their crests, so their heights add together into one unusually tall, steep wall of water. Such waves are rare and short-lived, collapsing as soon as the groups drift apart.
How does the Gulf Stream work?
The Gulf Stream works because winds and Earth's rotation push warm surface water from the tropical Atlantic toward Europe, creating a powerful ocean current. As it flows north, it releases heat to the atmosphere, keeping northwestern Europe milder than other regions at the same latitude.
How does permafrost form?
Permafrost forms when ground stays at or below 0°C for at least two consecutive years, locking soil, rock and water into a frozen state. The key mechanism is that winter cold penetrates deeper than summer warmth can thaw, so a permanently frozen layer builds up beneath the seasonally thawed surface.
How does an aquifer work?
An aquifer works as an underground water bank, where water from rain and rivers soaks into porous rock and fills the tiny spaces between grains. This stored water can then be pumped out through wells or flow naturally to springs, sustaining rivers and wetlands.
How does a well work?
A well works by tapping into groundwater stored in underground layers of soil and rock, called aquifers. Water seeps through permeable material into the well opening, and can be drawn up by a pump or bucket.
How do natural springs form?
A natural spring forms where groundwater flows to the surface through a permeable rock layer and exits at a point where the land dips below the water table. Springs appear where the water table meets the ground, often at hillsides, valleys or fault lines.
How does desalination work?
Desalination removes dissolved salt from seawater or brackish water by forcing water through a salt-rejecting membrane (reverse osmosis) or by boiling and recondensing it (thermal distillation). The result is fresh water, but the process needs large amounts of energy and leaves behind a concentrated brine that must be disposed of.
How does a water treatment plant work?
A water treatment plant cleans water by removing solids, dissolved impurities and germs in ordered stages. It first screens out large debris, then settles and filters particles, and finally disinfects the water before it is stored or piped to homes.
How does sewage treatment work?
Sewage treatment works by using physical, biological and chemical processes to remove solids, organic matter and pathogens from wastewater before it is returned to the environment. It typically involves primary settlement, secondary biological treatment and sometimes tertiary disinfection.
How does rainwater harvesting work?
Rainwater harvesting works by capturing rain that falls on surfaces like roofs and directing it into storage tanks or into the ground, rather than letting it run off. The collected water can be filtered and used for gardens, flushing, or with treatment, for drinking.
How does cloud seeding work?
Cloud seeding works by introducing tiny particles into clouds so that water vapour condenses or freezes onto them and grows into raindrops or snowflakes heavy enough to fall. It can only enhance precipitation from clouds that already contain enough moisture.
How does an anemometer work?
An anemometer measures wind speed by converting the wind's push on rotating cups or a spinning propeller into a rotation rate. The faster the wind, the faster the cups spin, and the instrument translates that spin into a speed reading.
How does a weather balloon work?
A weather balloon works by carrying instruments into the upper atmosphere to measure temperature, pressure, humidity and wind. The balloon rises because helium or hydrogen inside is less dense than air, and it bursts when the gas expands too much.
How does Doppler weather radar work?
Doppler weather radar sends out short pulses of microwave energy and listens for the echoes that bounce back from rain, snow and hail. By measuring the time delay, strength and slight frequency shift of each echo, it maps where precipitation is and how fast it is moving toward or away from the radar.
How do contrails form?
Contrails form when hot, humid exhaust from aircraft engines mixes with cold, low-pressure air at high altitudes, causing water vapour to condense and freeze into ice crystals. They persist when the surrounding air is already humid and cold enough to keep the ice from sublimating.
How does sleet form?
Sleet forms when snowflakes fall through a shallow layer of above-freezing air, partially melt into rain, then refreeze into ice pellets as they pass through a deeper sub-zero layer near the ground. The result is small, translucent ice pellets that bounce when they hit a surface.
How does an ice age happen?
An ice age happens when global temperatures fall enough for ice sheets to expand across continents, driven mainly by slow changes in Earth's orbit and axis that reduce summer sunlight in the northern hemisphere. These orbital cycles, combined with feedbacks like higher reflectivity from snow and lower greenhouse gases, can sustain glacial conditions for tens of thousands of years.
Why does turbulence happen on planes?
Turbulence happens when an aircraft flies through air that contains irregular, chaotic motions, such as eddies and swirls. These disturbances create uneven forces on the wings, causing the bumpy ride.
How does a barometer work?
A barometer measures air pressure by letting the weight of the atmosphere push against something that responds measurably, such as a column of mercury or a sealed metal capsule. Rising or falling readings show whether air pressure is changing, which helps forecasters predict weather and lets instruments estimate altitude.
Key ideas behind them
What is the water cycle?
The water cycle is the continuous journey water takes through the environment — evaporating from oceans and land, condensing into clouds, falling as rain or snow, and flowing back to the sea. The same water has been recycled for billions of years.
What are tides?
Tides are the regular rise and fall of the ocean's surface, caused mainly by the Moon's gravity pulling on Earth's water. As Earth rotates, most coasts get two high tides and two low tides each day.
What are ocean currents?
Ocean currents are large, continuous flows of seawater driven by wind, temperature, salt, and Earth's rotation. They move heat around the globe, shaping climates — like the Gulf Stream warming Western Europe — and carrying nutrients that support marine life.
What is the Coriolis effect?
The Coriolis effect is the way Earth's rotation bends the path of moving things like wind and ocean currents. Instead of traveling straight, they curve — to the right in the Northern Hemisphere and left in the Southern — shaping weather systems and hurricanes.
What is El Niño?
El Niño is a natural climate pattern in which the central and eastern Pacific Ocean becomes unusually warm, shifting weather worldwide. It can bring floods to some regions and droughts to others, disrupting rainfall, fishing, and temperatures across the globe.
What is a cloud?
A cloud is a visible mass of tiny water droplets or ice crystals floating in the sky. Clouds form when warm, moist air rises, cools, and the water vapour it carries condenses onto tiny particles into droplets too small to fall.
What is rain?
Rain is liquid water that falls from clouds when droplets grow big and heavy enough to drop out of the sky. It's a key step in the water cycle, returning water from the atmosphere back to the land and oceans.
What is weather?
Weather is the short-term state of the atmosphere in a place — its temperature, rain, wind, humidity, and cloud cover at a given moment. It changes hour to hour and day to day, unlike climate, which is the average weather over many years.
What is climate?
Climate is the long-term average pattern of weather in a place, measured over decades — its typical temperature, rainfall, and seasons. While weather changes day to day, climate describes what conditions a region can usually expect.
What is surface tension?
Surface tension is the 'skin-like' force at the surface of a liquid, caused by its molecules pulling on each other. It's why water forms droplets, why some insects can walk on water, and why a gently placed paperclip can float.
What is capillary action?
Capillary action is the ability of a liquid to flow upward through narrow spaces against gravity, like water climbing up a thin tube or a paper towel. It happens because the liquid's molecules are attracted to the surface and to each other.
What is evaporation?
Evaporation is the process by which a liquid slowly turns into a gas at its surface, below its boiling point. It happens when the fastest-moving particles at the surface gain enough energy to escape into the air — which is how puddles dry up and wet clothes get dry.
What is a tornado?
A tornado is a violently rotating column of air that reaches from a thunderstorm down to the ground. Though small compared with a hurricane, a tornado packs the fastest winds on Earth and can destroy almost anything in its narrow path.
What is a hurricane?
A hurricane is a huge, spinning storm that forms over warm ocean water, with powerful winds and heavy rain rotating around a calm center called the eye. The same kind of storm is called a typhoon in the northwest Pacific and a cyclone in the Indian Ocean.
What is a tsunami?
A tsunami is a series of huge ocean waves caused by a sudden disturbance of the sea floor — usually a large undersea earthquake. In deep water the waves are low and fast; as they reach shallow coastlines they slow down and pile up into towering, destructive walls of water.
हिंदी में पढ़ें: भँवर कैसे बनता है? · ज्वार-भाटा कैसे काम करता है? · बांध कैसे काम करता है? · क्विकसैंड (चलती रेत) कैसे काम करता है? · जल चक्र कैसे काम करता है? · वाष्पीकरण कैसे काम करता है? · भँवर कैसे बनता है? · तूफ़ान (हरिकेन) कैसे बनता है?
Frequently asked questions
What causes a whirlpool?
A whirlpool forms when water is set spinning, usually where opposing currents or tides meet, or where water drains through a narrow opening. As the water spirals inward it speeds up, like a spinning skater pulling in their arms.
Why do tides happen twice a day?
The Moon's gravity pulls the ocean into a bulge on the side facing it, and a second bulge forms on the far side. As Earth rotates through both bulges, most coasts see two high tides and two low tides roughly every 24 hours and 50 minutes.
Is quicksand really dangerous?
Quicksand is rarely deep enough to swallow a person, and the human body is less dense than the sand–water mix, so you float partway. The real risks are getting stuck as tides come in, or exhaustion from struggling.