How do I make a geyser?

Pour lava straight into the middle of the lake, or under any deep pool of water. The water touching the lava flashes to steam and blasts the water above it into the air.

Why did my water disappear?

It probably touched fire, lava or hot obsidian and boiled into steam. Steam rises, gathers at the top of the page and falls back as rain.

Can I save my creation?

Yes. Your world and your notebook are saved in this browser automatically. Press save to turn the world into a picture you can download or share.

Does it work on a phone?

Yes. Pick a paint and draw with your finger. The cells are a little smaller on phones so the world stays detailed.

Sandpit

Pour, burn, melt, grow. Every grain is simulated. Back to the game

How to play

Pick a paint from the paint box and draw on the page. Hold still to keep pouring. Number keys 1 to 9 pick paints, 0 is the eraser, the space bar pauses time and N opens your notebook.

The notebook in the corner lists nine reactions to find, each with a hint. When one happens, it gets written up and ticked in red pen. Your world and your notebook are saved in this browser, so you can come back to them. Save turns your world into a picture you can download or share. Reset brings back the starting scene.

What reacts with what

Fire spreads through wood, plants and especially oil, and leaves smoke behind.
Water puts out fire as a puff of steam. Poured on lava, it cools it so fast that it sets as black obsidian, which stays hot for a while.
Lava sets fire to anything that burns, melts ice and turns the sand it touches into glass. Pour it under deep water and the water flashes to steam and bursts up as a geyser.
Oil is lighter than water, so it floats on top. It also burns fast.
Seeds fall like sand and sprout when they land near water. Plants drink water and grow up into the air, and sometimes flower.
Ice melts near heat and slowly freezes the water touching it.
Steam rises, gathers under the top of the page as a cloud and falls back as rain.

How does it work?

The world is a grid of tiny cells, and each one holds a single element. Many times a second, every cell follows a few simple rules, and some elements change when they touch others.

There is no code for a waterfall or a forest fire. They just happen when enough cells follow these rules, which is the whole charm of falling-sand games. (The volcano is a small cheat: it gets a steady push of magma from below.) The idea goes back to the 1990s and became a craze in the mid-2000s with browser games like Falling Sand Game and Powder Game.

A little real science

Real lava does turn into rock when water cools it: that’s how new land forms in Hawaii and Iceland. When lava cools too fast for crystals to grow, it becomes volcanic glass, and obsidian is the best-known kind. Ordinary glass is mostly melted sand (silica): glassworks add soda and lime and melt it at about 1,500 °C, while pure silica needs over 1,700 °C. A geyser works like a buried kettle: groundwater heated deep underground boils, and the steam throws the water above it into the air. Old Faithful in Yellowstone does this roughly every 60 to 110 minutes.

Questions people ask

How do I make a geyser?: Pour lava straight into the middle of the lake, or under any deep pool of water. The water touching the lava flashes to steam and blasts the water above it into the air.
Why did my water disappear?: It probably touched fire, lava or hot obsidian and boiled into steam. Steam rises, gathers at the top of the page and falls back as rain.
Can I save my creation?: Yes. Your world and your notebook are saved in this browser automatically. Press save to turn the world into a picture you can download or share.
Does it work on a phone?: Yes. Pick a paint and draw with your finger. The cells are a little smaller on phones so the world stays detailed.