Saturday, 28 February 2015

Under the volcano - visiting Reunion's lava tubes

Fancy visiting the bowels of the earth? Crawling under a volcano along tunnels that were still molten magma just over a decade ago? This is what you can do when you visit Reunion's lava tubes.

Looking out to sea from the starting point

Although lava tubes are located all over Reunion, access to most of them is to be found in the island's south-east, in an area known as Le Grand Brûlé. This is where lava sometimes flows from the Piton de la Fournaise into the sea.

ʻAʻā lava to the left, pāhoehoe lava to the right

The particular lava tube that we visited dates from a 2004 eruption, eleven years ago. I believe that is the most recent lava tube in the world that can be visited by the public. Reunion's lava tubes are also fairly unique in that they are easy to access and show a large variety of geological forms. Elsewhere in the world lava tubes can be found in Iceland, Azores, Canary Islands, and the USA.

Tree bark imprint on lava

Although some people visit the tubes by themselves, it's highly recommended to go with a professional, which is what we did. We had been asked to wear trousers and closed shoes, and he equipped us with gloves, hardhats, headlamps and optional elbow and knee pads. Our meeting point was at the nearby Vierge au Parasol: the statue of a madonna holding a blue parasol. According to legend a local farmer placed this statue in his fields, hoping his crops would be protected from destruction by the volcano. Following an eruption he found that although lava had flowed through his fields the statue had miraculously been spared. 

Vierge au parasol (source)

Our guide, a trained speleologist, told us he knew of 22 entrances to the lava tube we were visiting that day; however we only used two - one to get in and one to get out!

Lava tube entrance 

We opted for the 3-hour 'discovery' visit, which covers about 1.6 km (1 mile). The same company also offers a 5-hr 'classic' and a 6-hr 'sporty' visit.

Inside the entrance looking out

A lava tube is a natural conduit formed by active low-viscosity lava which flows beneath the hardened surface of a crust or roof of lava. 

walking down the tube

When the supply of lava stops after an eruption or if lava is diverted elsewhere, lava in the tube system drains downslope and leaves partially empty, long, cave-like channels beneath the ground.

walking down the tube

Lava stalactites and stalagmites are known indifferently as 'lavacicles' and form in lava tubes while lava is still active inside. The formation of lava stalactites happens very quickly in only a matter of hours, days, or weeks, (whereas limestone stalactites may take thousands of years to form). A key difference with lava stalactites is that once the lava has stopped flowing the stalactites cease to grow, so if the lavacicle is broken it will never grow back.

shark's tooth-shaped lavacicles

We saw several examples of what is called perimorphosis, which occurs when an object, in this case a tree trunk, leaves an empty cast in volcanic flow.

example of perimorphosis

The lava sometimes leaves peculiar shapes, such as a dodo; at one point we even saw what looked liked a giant slice of chocolate cake!

does this look like a shark's head to you?

can you see a lion's head, complete with mane?

A rare characteristic that can occasionally be seen is lava pillars. Lava pillars are hollow inside, forming a pipe-like channel between the bottom and the top of a lava flow. 

A small lava pillar

The tube was always wide, but sometimes not very high. Most of the time we could walk along it normally, but not always. I'm 5'1" and reasonably athletic so I never had to go down on my hands and knees (if necessary I moved forward using an ungainly squatting position!) but some people preferred crawling. At a few places our guide indicated alternative narrow side tubes that the thrill-seekers in our group could wriggle along.

crawling along a narrower alternative route

It was surprisingly hot inside the tube (more or less the same temperature as outside, so high 20s°C), and the humidity level was high too (100%).

wall detail

In several places we saw thin roots of vegetation hanging down.

wall detail

If it rains it only takes about 30 minutes for the rain to filter through into the tube, and it can take up to three weeks for it to stop dripping afterwards.

roof detail

One of most memorable moments was before turning back, when we all sat down and turned off our headlamps. We found ourselves in complete and utter pitch darkness, which is something you realise you very rarely experience ...

roof detail

After a fascinating morning we were nevertheless happy to be back in our natural element - with natural light and fresh air!

Bois de rempart trees are the first endemic species to colonise a lava flow after an eruption

Note that visiting the lava tubes is not recommended for claustrophobics or people with heart, breathing, knee or back problems.

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