Future finders please note the tasks you must complete to log this EC and the tools you’ll need to complete these tasks. I have had far to many finders sending incomplete info when clearly they have just turned up and hoped for the best. Earth caches are there for a reason, or learn something. All the info about earth caches is here. I will not be accepting finds on this earth cache if you do not supply the correct info.
Earth caches aren’t there just to pad your ‘found it’ numbers.
Please Note: the photos shown here are of lava caves on Rangitoto but are not of the cave that you will explore for this cache (so as not to be spoilers). Also, this cache is accessible to "the general public" i.e. all reasonably able bodied persons without the need for any special equipment. The caves shown in the pictures require special equipment but are included for interest.
Rangitoto Lava Caves
On Rangitoto most of the lava flows are of the rough textured a'a type, in which molten lava slowly moved along inside a thick tube. The outside of this tube is a crust of broken-up chilled lava. Sometimes lava caves form when hot lava drains out from inside the solidified outer crust of the flows leaving hollow tubes. There are about 7 known lava caves on Rangitoto, some of which are sign-posted and worth a visit.
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like channel.
Lava usually leaves the point of eruption in channels. These channels tend to stay very hot as their surroundings cool. This means they slowly develop walls around them as the surrounding lava cools and/or as the channel melts its way deeper. These channels can get deep enough to crust over, forming an insulating tube that keeps the lava molten and serves as a conduit for the flowing lava. These types of lava tubes tend to be closer to the lava eruption point.
A broad lava-flow field often consists of a main lava tube and a series of smaller tubes that supply lava to the front of one or more separate flows. When the supply of lava stops at the end of an eruption or lava is diverted elsewhere, lava in the tube system drains down slope and leaves partially empty cave-like conduits beneath the ground.
Lava tubes can be up to 14-15m wide, though are often narrower, and run anywhere from 1-15 m below the surface. Within the Auckland volcanic field more than 50 lava tubes and other lava caves have been discovered, including the 290 metre long Wiri Lava Cave.
To claim this cache you must provide the following information to the cache owner by e-mail and await confirmation that the answers are correct. Please do NOT post the answers in a log.
- At the entrance (above co-ordinates) describe the shape of the cave and the approximate diameter in feet
- At the exit describe the shape and approximate height in feet
- Approximately how many meters (paces) from entrance to exit
- Describe the feature at 40 metres
- Describe the compass direction of the lava flow