A caldera is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the structural integrity of such a chamber, greatly diminishing its capacity to support its own roof, and any substrate or rock resting above. The ground surface then collapses into the emptied or partially emptied magma chamber, leaving a large depression at the surface. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact. Compared to the thousands of volcanic eruptions that occur over the course of a century, the formation of a caldera is a rare event, occurring only a few times within a given window of 100 years. Only seven caldera-forming collapses are known to have occurred between 1911 and 2016. More recently, a caldera collapse occurred at Kīlauea, Hawaii in 2018.

किसी ज्वालामुखी के विस्फोट के परिणाम स्वरूप अस्तित्व में आई एक कुण्ड या पात्र सदृश रचना भूवैज्ञानिक भाषा में ज्वालामुख-कुण्ड कहलाती है। अंग्रेजी और अन्य यूरोपीय भाषायों मे इसे कैल्डेरा (Caldera) कहते हैं, जो एक स्पैनिश शब्द है पर इसका मूल लैटिन भाषा के कैल्डेरिया में निहित है जिसका अर्थ 'खाना पकाने का बर्तन' होता है।।