On the hottest May day since records began I went with some friends to trace the Huangxi River in Yangmingshan. We used this excellent blog post as a rough guide. Normally I would leave it at that however we went further than that post, right through the beautiful slot canyon. I also did a ton of research on everything from butterflies to volcanism and I feel I may as well share it. If you're just interested in the river trace details follow the bold text. A note on names: The stream referred to as Shuanghuang on the post is called Bayan Stream on the official Yangmingshan map. That post mentions some naming confusion too. I'm going to use Bayan in case you are using the same map.
Nerdy Bit on the Yangmingshan Volcanoes:
Called the Datun group there are roughly 20 volcanoes over 8 vent systems here. The group as a whole is classed as dormant. Some studies have put their last eruption at about 5000 years ago, others at 20'000, and some more at 100-200'000. There seems to be a lot of disagreement in the scientific community about this and also about what is classed as an eruption and what is mere “volcanic activity”. The youngest and tallest volcano is Qixingshan in the center of the group. Qixing also has the most active fumeroles, jets of superheated gas and sulfur, on its sides. A new one opened recently and there have been some mid-sized shallow earthquakes under the mountains in the last few years. This has predictably led to media sensationalism and panic.
The whole system has a large magma chamber underneath it. This is normal and geologists do not think this is an immediate threat. Some consider it to be cooling and shrinking, though the more I read about that the less sure it seems. The presence of the fumeroles was clear evidence of the chamber anyhow and the studies were just trying to work out where it is. The most recent findings puts the magma chamber at about 12km underground. However there may be a few shallower spurs that are heating the ground nearer to the surface along the Jinshan Fault. Eruptions are not something to really worry about though. The volcanoes here erupt highly viscous andesitic lava, which is slow and hardens easily. The danger would be if the lava solidified into a lava dome. Behind this pressure could build up and then release in a violent pyroclastic explosion. However, prior to this ground swelling and degassing would be visible so local people would have plenty of warning. One way to tell if a volcano is gearing up for an eruption is to monitor the temperature of fumeroles. Although there is a station monitoring volcanic activity here I can't find their data. The only Taiwanese volcano that has had definite recent eruptions (but just 4 in the last 7000 years) is Guishan in Yilan. Otherwise known as Turtle Island.
The Huangxi River
One of the most distinctive rivers in Taiwan is the orange Huangxi River. It's name means sulfur creek. The path down to here described in the Beaten Track post has been closed for over a year now after villagers got irritated by weekend crowds. Instead take the trail starting near the Bayan Hot Springs Hotel and walk up the river. Bus 1717 from Taipei stops nearby. The trail will arrive at a stream crossed by a log and a rope. The path continues uphill to the Bayan Wild Hot Springs but this is the entry point for the Huangxi river trace. Drop down into the orange river and head upstream. Make sure there're no storms forecast and you have the correct river shoes with the felt bottoms.
Nerdy Bit on the Rock Color
Unlike the orange color of the Golden Waterfall in Jinguashi the color here is natural. The Jinguashi River is a browny-orange because of minerals and metals leaching out of abandoned mineshafts. It's also fairly toxic. In Yangmingshan, a bubbling hot trickle coming out of the Dayoukeng fumerole field and joins the Bayan Creek then later the Huangxi. Fumerole fields typically hold about 200-300 different minerals, though the dominant element is sulfur. Chalcophiles like zinc react with the sulfur creating sulfides in a range of colors from orange to crimson. We noticed a few deep red pools along with the orange and yellow stains. I'm unsure whether some of the sulphides in the water are dangerous or not. People bathe in hot spring water from the same sources so I assume (and hope) any toxic minerals are merely trace amounts.
The trace isn't technically very difficult but there are very few flat areas. Near a large pool there's a huge chunk of sulfur stained rock and the smell of rotten eggs in the air. A bare patch on a nearby hill looks like the candidate for the source. I believe this is a small unnamed fumerole. It's not super far from the larger vent field at Bayan.
After over an hour of scrambling we came to a beautiful spot where the Bayan Creek joins the Huangxi. Above here, with no sulfur source, the boulders of the Huangxi are a bright gray We headed up the Bayan over a series of small waterfalls and the valley began to narrow.
Nerdy Bit on Butterflies
There had been a few flocks of butterflies on other parts of the river but here we encountered a group of over a hundred. The dominant species here was the bluebottle (G.S connectens), which is a type of swallowtail butterfly. It's the most common butterfly in Taiwan. There were also a lot of a plainer white butterflies which I'm not confident I know the species of. Butterflies often gather on wet or rotting matter to suck up nutrients like amino acids. This is known as 'mud-puddling'. Interestingly the bluebottle has incredible vision, with a lot more photoreceptors than other species of insect. They use the patterns on their wings for communication so it must be beneficial to see many subtle differences.
After disturbing the butterflies we headed into a slot canyon not unlike the now famous and much more accessible Wormhole near Pingxi. The tall green walls and shaded pools were welcome after the exposed sections of the lower river. The highlight of this section of river came into view. A huge boulder the size of a house is wedged between the walls of the canyon. There's a gap underneath where the river flows through creating a sort of cave.
At the other side of the cave a small but wide waterfall created a barrier but with the water level quite low it wasn't too hard to pull ourselves up. The canyon above is a scenic series of narrow waterfalls and deep pools. At one point a couple of boulders made a precarious arch.
This part of the river was very enjoyable with a perfect balance of scenery and challenge. Right at the top of the canyon, where the river again becomes wide, we came to an impassable obstacle. This waterfall was just a little too tall to climb and the rocks around the side too high and slippery. From the looks of things the river further up is fairly wide and plain and after a few bends just reaches the road near the start of the Jinbaoli Trail. We headed back down.
To have a closer look at the route check the Hidden Taiwan Map.