Gateway to the underworld: Permafrost 'megaslump' in Siberia is expanding According to a study published in the Journal of Geomorphology, global warming is the cause of the enlargement of the Batagaika crater in Siberia. Also known as the "gate to hell", this crater releases thousands of tonnes of CO2 each year and is expanding at record speed. FRANCE 24's Julia Sieger tells us more.