Caldeira Segara Anak, Volcanic caldera in Lombok, Indonesia.

Caldeira Segara Anak is a caldera on the island of Lombok whose western part is filled by the waters of Lake Segara Anak. Its eastern rim is topped by Mount Rinjani, an active volcano reaching 3,726 metres. The depression formed when the Samalas volcano, about 4,200 metres high and 8 to 9 kilometres wide, collapsed in 1257.

Caldeira Segara Anak formed when the Samalas volcano, about 4,200 m high and 8 to 9 km wide, collapsed in 1257. The eruption sent an ash plume modelled at 43 km altitude and pyroclastic flows up to 25 km, with a Volcanic Explosivity Index of 7. The Lombok kingdom's capital, Pamatan, was buried like Pompeii and its site is still sought.

The name Segara Anak means "child of the sea" in Sasak, referring to the lake that fills the western part of the caldera. The 1257 collapse of Samalas buried Pamatan, the capital of the Lombok kingdom, in the manner of Pompeii; its site is still being sought. The eruption was identified in 2013 from volcanic ash trapped in Greenland ice cores.

The caldera lies on Lombok, with the Segara Anak lake filling its western part and Mount Rinjani rising on the eastern rim to 3,726 metres. Reaching the rim means a multi-day trek, so go with local guides and carry supplies for the whole route.

The 1257 Samalas eruption that carved this caldera was identified in 2013 from volcanic ash trapped in Greenland ice cores drilled by coring. Modellers estimate its plume reached 43 kilometres high, and some researchers argue it was a main factor in the onset of the Little Ice Age.