Wai Sano is a volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 located in the western part of the island of Flores

Flores

Flores is one of the Lesser Sunda Islands, an island arc with an estimated area of 14,300 km² extending east from the Java island of Indonesia. The population was 1.831.000 in the 2010 census and the largest town is Maumere. Flores is Portuguese for "flowers".Flores is located east of Sumbawa...

, Indonesia

Indonesia

Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

. Wai Sano consists of an elliptical caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 about one mile (2.5 km) wide, containing a lake 260 meters below the 903 meter caldera rim, itself part of Mount Umpu Rua. Two fumaroles are located on the southesastern shore of the lake. No historical eruptions are known.