Foulden Maar was created 23-million-years-ago when a volcano erupted to form a shallow crater that filled with water. Over time, the bottom of the lake was built up with layers of microscopic algae to create a diatomite deposit. This also contains a wealth of fossils and historic climate data, spanning hundreds of thousands of years.
Foulden Maar is subject to a controversial mining proposal that has attracted public opposition.
To take action, you are welcome to sign the petition.