Image copyright Getty Images Image caption Unlike this, the lava tube the man fell into appears to have been hidden

A man in Hawaii has died after falling down a "lava tube" - a tunnel formed by volcanic eruptions - while trimming trees on his property.

Police say the 71-year-old had apparently fallen about 22ft (7m) "through a soft area of ground".

Lava tubes are formed when lava cools and hardens on its top layer but continues to drain and cool beneath.

Police say the man was found on Monday after friends reported that they had not heard from him for days.

Image copyright Getty Images Image caption Lava tubes are common in Hawaii and some have "skylights" to the surface that can be covered by brush

Hawaii Police Department Major Robert Wagner told Big Island Now that the shaft the man fell into was approximately two feet (60cm) wide.

Fire crews abseiled into the chasm to recover the body.

Media playback is unsupported on your device Media caption Mesmerising lava lake overflow in Hawaii

Unlike slower forming geological features, like caves and caverns, lava tubes are often formed in days and weeks, according to National Geographic.

As that lava flows and drains into the ocean, it leaves behind maze-like tunnels - some of which are over 40 miles long.