Undara Volcanic is a national park in North Queensland, Australia and is notable for its lava tubes and gem fossicking. Minerals found there include topaz, moonstone, peridot, aquamarine, garnet, quartz and gold. The park contains the remains of the Earth’s longest flow of lava originating from a single volcano. The park is remote, and accessible from the regional centres of Townsville or Cairns. The area is situated within the McBride volcanic province and contains 164 volcanoes, vents and cones. The lava tubes are regarded amongst the largest and longest on the planet. The word Undara is aboriginal in origin and means a long way.
The volcanic activity that formed the tubes occurred approximately 190,000 years ago and the volcano Undara expelled massive amounts of lava onto the surrounding Atherton Tableland. In total it was estimated that over 23 billion cubic metres of lava that was released covering an area of 55 sq km. Bayliss Cave is the remains of a lava tube that was once over 100 kilometres (62 mi) in length. The cave itslf is over 1,300 metres (4,265 ft) in length, 11 metres (36 ft) high and 22 metres (72 ft) wide. It is described as a "bad air cave" with Carbon Dioxide levels having been measured as high as 5.9%.