Kazumura Cave is the longest cave in which U.S. state?

Kazumura Cave is a lava tube and has been surveyed at 40.7 miles (65.5 km) long and 3,614 feet (1,102 m) deep making it the longest and deepest lava tube in the world. The cave is located on the island of Hawaii on the eastern slope of Kilauea. Kilauea is the most recently active volcano on the Big Island. The Aila'au lava flow that contains Kazumura Cave originated from the Kilauea Iki Crater about 500 years ago.

By 1993, a single year of extensive surveying established that it was the longest in the world. Originally Kazumura was two separate caves known as Upper Kazumura and Old Kazumura. Kevin Allred and Mike Meyer connected the two caves after seeing a small connection between the two caves and enlarging it to permit entry. More connections were made later at Paradise Park Cave when it was connected to Kazumura through a breakdown pile. Later, a culvert was installed to keep the passage stable.

The Kazumura Cave Atlas lists 101 entrances, all on private property. Under current Hawaiian laws, landowners must be asked before entering any lava tubes on their property. At least one landowner runs paid adventure tours through his section of the cave as of 2016.