The Volcanic Island of Jeju (Part 3)

South Korea > Jeju

August 2013

Okay, before we leave Seongsan Ilchulbong for good, the Leap of Approval!

We are soon on our way to the 3rd and final location inscribed by the UNESCO World Heritage Site — the lava caves of Manjanggul.

It’s officially called ‘lava tube’ here, but the terms ‘cave’ and ‘tube’ are synonymous. Caves are really big tubes, after all.

Let me try to explain. Several hundreds of thousands of years ago, lava flowed out of the huge magma chambers underneath present-day Jeju Island — some entered caves to flow like thick liquid in a pipe. The Manjanggul lava cave or tube is the remnant of such a cave.

Manjanggul cave is many kilometers long, but only a 1-km stretch is open to the public. So the idea is to walk 1km to the end, make a U-turn and return to the entrance — a total of 2km.

Entrance is a hole in the ground (see diagram above) and we gingerly descend two sets of staircases into a dark and, surprisingly, cool and less-humid environment. It’s like being thrust into a dungeon with climate control in place. It is a truly pleasant surprise as the surface has been hot and humid.

Imagine if you will, red hot lava flowing through this way, possibly up to 1,200°C. Truly terrifying.

As it flowed, it left marks on the walls of the cave. The floor is obviously left-over stagnant lava which had solidified into some igneous rock, most likely basalt in this case — very hard stuff. Walking can be treacherous, so if you plan to visit, please wear appropriate footwear.

On the sides I notice these somewhat parallel lines.

Here it is very prominent.

It turns out these are lava flow-lines. At various times, the lava flowed at a certain height and this was marked on the wall. The many lines indicate the levels fluctuated, and this case continually receding lava levels.

And the floor … lava rock everywhere. Can get slippery and there are sharp edges too, so wear proper shoes. Thongs or slippers a no-no.

When extremely hot lava flowed through a cave, there’s a whole lot of interesting geology to explore, such as these little ‘stalactites’.

The hot temperature of the lava sometimes caused the roof and sides of the cave to melt, and the molten goo dripped down, to form these rock stalactites.

Of course the stalactites could form lava stalagmites on the cave floor … just like in limestone caves, except that here they are sharp hard rocks.

This is a huge passage with the usual markings on the walls … just imagine the amount of red lava which flowed through it. This high-ceiling feature is called the ‘cupola’.

Very spectacular indeed … some say this is the best lava cave in the world which is open to the public. I’m suitably impressed, and I’m not an easy person to impress.

In some sections, there are rockfalls, obviously from after the lava had stopped flowing. Otherwise they would have been swept away by the lava river.

Again the rough lava rock walkway which is sometimes hard on the ankle. So please be very careful if you come here.

Solidified lava from hundreds of thousands of years ago. Amazing stuff!

Here’s more rockfall, and a safe boardwalk for us to amble past has been built.

Now this is a real tube! See the lava markings on the sides.

Funny that the lava rock floor looks like a makeshift cement road.

This is Turtle Rock, which has become an icon of Manjanggul Lava Cave. It was actually a lava raft — a blob of lava from another tube above this one, which had dropped onto the flowing lava here and floated, whence the term ‘raft’. In the Turtle Rock’s case, it settled down at this spot as the lava flow slowed down, but some minor lava slow still caused the flowline marks on its sides.

These are not lava flowlines, but lava shelves. There were formed when hot lava met less hot walls, and solidified. Depending on their shapes, they can be called lava balconies or lava benches. Great geology!

More lava shelves along the way.

These are not elephant dungs, but lava which dropped here from another tube above.  They are called lava toes.

Another stretch of the cave with very nicely-done metal boardwalk.

Hmmm … a mixture of lava flowlines and lava shelves? The vertical lines are actually lava flowstones — molten bits of the walls and ceiling which drips down the sides.

Now I can see the end of the passage — we are 1km from the entrance, and after 30min of very interesting stroll in the darkness of the cool and damp cave.

What a way to end the show — a 7.6m lava column said to be the biggest in the world!

Time to make a U-turn and return to the cave entrance, but I love these lighted World Heritage Site logos lining the handrails of the boardwalk. Very nice touch indeed!

Another blob of lava which dropped from a tube above this one. These fallen lavas really look like piles of dung.

The stroll back to the entrance is like a rerun of an excellent NatGeo documentary.

Looks like exposed roof — maybe the rockfall happened when lava was still flowing, thus no debris is in sight.

Back to the surface and the heat and humidity hit us hard — but a very educational 2km walk done in an hour. Thoroughly recommended even if you hate geology or geography, or school.

Time to recharge some missing key ions. In this heat and humidity, rejuvenate yourself with this stuff — normal mineral water just doesn’t cut it.

Some 20min later we are back in Jeju City.

And yes, the ubiquitous black lava rock at the beaches. We know what it had been up to!



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