Viewed from a plane, clouds appear fluffy and light, but in fact the water droplets and ice crystals making up the average cumulus cloud (1km cubed in size) weigh around 550 tonnes – the same as a herd of 100 African elephants.

Meanwhile, a towering thunderstorm cloud is equivalent to 200,000 elephants. So how do these great beasts stay up in the sky?

If a cumulus cloud was a lump weighing 550 tonnes, then it would fall down with a thud. But in fact a cloud is made up from millions of minute droplets – each about 100th of the width of an average raindrop.

Those tiny droplets do fall, but because they are so small their terminal velocity (the balance between gravity and the air resistance around the droplet) is a mere 900cm per hour or so. To fall from 2,700m (8,850ft) – a typical altitude for a cumulus cloud – would take more than 12 days in calm conditions.

But of course the environment around most clouds is far from calm: clouds tend to form in places where warm air is rising. For an average cumulus cloud this updraft can be several metres per second – enough to keep most small droplets aloft.

This balance between the updraft and the speed of the falling droplets is partly responsible for the shapes and textures of the clouds we see. Sometimes heavier ice crystals plummet downwards, creating wispy cirrus clouds.

And once tiny water droplets start to club together they eventually become big enough to gather speed and fall as rain.