Tag Archives: geology of Saitama

Caves of Saitama

Earlier this month I set off for another exploration of the nature in the Chichibu mountain area of western Saitama Prefecture. The original plan had been to visit a canyon I had encountered during the spring. But too many short nights left my body in need of sleep and I had to thank the cat for waking me up at 5 am since I apparently shut off my 4:30 alarm and dozed right off again. So, a late start, and then my plans were thwarted once more as I crossed into Chichibu and found fog in the valley. This led me to make the fruitless decision to head up a road for a view, but I missed the turn and got on a road that led to no view of the valley. After losing another 30 minutes, I decided I was out of time for driving way in to find that canyon. So, as I drove up R140 and thought of where to go, I spied the Kaminiwa Cave across the river and up the slope.

The Kaminiwa Cave is actually two caves close together, one of them referred to as a “half cave” (半洞窟). They have formed in a limestone cliff and are said to have been eroded by the Ara River (Arakawa 荒川) some 50,000 years ago. The cave was used during the Jomon Period by hunters as a shelter while they were away on hunting trips.

Access to the cave is from either downstream by the large torii gate where the path leads up to the trailhead to the route up to Mitsumine Shrine, or further upstream at a campground with a free day-use area. I came in from this way and followed a path a short distance to the cave. At first it appeared to be just a wide hollow under an overhanging cliff face. But I soon discovered there was a low passageway leading to an opening that led to a small but open chamber. To one side, a narrow corridor ran a short distance to a very narrow gap in the rocks with a view to a corridor beyond that soon turned right and disappeared into the darkness. I had only the light of my smartphone to illuminate the inside, though reflected sunlight came in enough to provide a very dim light. A couple of cave crickets sat on the wall at one end where a small gap revealed darkness beyond.

The second cave has a very high opening that has been partly closed with concrete with a door opening cut in. Once inside, it would seem like there’s only this open chamber with a vaulted ceiling. But on the left there are what look like steps cut into the limestone layers. Two large screws with loops for running ropes through were jutting out from the rocks. above the steps, there was a deep shadow. I crouched down and saw that the steps led up a narrow chimney. Holding my light up, I poked my head up into the opening and found a small chamber opened up above. There was a dark opening at the end that suggested that there was another chamber. I was about to clamber up when I noticed two bats were hanging from the ceiling. I wondered how they would respond to my intrusion. I didn’t want to disturb them. But if they began fluttering about, would they panic with a large moving object blocking their entrance? Would they pee on me? Where there more bats in the next chamber? I decided to duck back down again and make a note to return in the future with a proper light, perhaps at night when the bats would likely be out.

There are several caves around Saitama. Perhaps the most famous one is the Hashidate Limestone Cave near Urayamaguchi Station and the Urayama Dam. For a small fee, you can enter this cave, going in via a low tunnel that leads to a large open chamber with interesting cave formations. These formations do not rival Japan’s more famous famous caves but they are still interesting. There are some other shallow caves I have found while out driving, some of them marked on the map or with a trail marker, a couple not marked. Saitama’s longest cave is 2.1 km and it’s found somewhere in the Yakemame Ravine, just before R140 disappears into the long tunnel that leads to Yamanashi. This cave is not open to the general public, but I did try to find my way – unsuccessfully – into the ravine last summer. Inspired by my recent cave visit, I will be looking for more.

The mountains of Saitama are largely composed of ancient ocean sediments. Limestone, chert, sandstone, mudstone, and the metamorposed crystalline schist of the Sanbagawa Metamorphic Belt were all laid down way back in the eons past when this area was a seabed. Not only caves, but limestone mountains are also found in the area. The most famous is Bukosan, which is mined for its limestone to make concrete. Futagoyama is a mountain on a limestone ridge that has two steep-sided peaks. The Nakatsukawa Ravine also has many limestone cliffs and at least two caves that I know of.

Photos I took of the caves and mountains can be found on Flickr.

Here are two photos from the Hashidate Cave from an older post from many years ago.

Cave growth – Hashidate Cave
Into the limestone cave – Hashidate Cave

Inspection of the Arima Gorge and the Shiraiwa Ravine

January 2nd, 2020. My first outing of the year. Even with the completion of my book of Saitama scenic photographs, I continue my exploration of the mountains of my prefecture of residence. The plan was to find a viewpoint of some mountains I visited two years ago and be there before sunrise. However, I accidentally entered the wrong location into the navigation computer and ended up arriving an full 30 minutes after sunrise at an insignificant mountain pass with no view, the road sloping downward before me toward the Tokyo border.

I decided to go on free exploratory mode and simply go where I thought I might find something to study and possibly photograph. My first stop was the dam at Lake Naguri in Hanno City. After a brief view from the dam, I started up the engine and drove fifty metres to a road block. It seems that Typhoon Hagibis (a.k.a. Typhoon #19 because it was the nineteenth typhoon of 2019) had caused a landslide right behind the dam administration office and effectively cut off the road around the north side of the lake.

IMG_3578 I had to drive across the dam and up the road on the south side. I had decided to drive up a small forestry road that twisted and turned across the upper mountain ridges cutting very close to the 800m high peaks before slithering back down to Route 53, which was the way I had come up before turning off to the dam in the first place. It looked promising until I hit a chained off road on the right and was forced to turn left. Well, we would see where this route led.

As I drove, I spied some layers of sediments alongside the Arima River. They were rather pronounced and I stopped to grab a few snaps.

As I drove more, the sediments continued to catch my attention. In all my explorations of ravines and gorges in Japan, I have never seen such pronounced and persistent sedimentary deposits. What was especially puzzling was that trees seemed to be growing up through these sediments as though the mix of rocks, gravel and sand had been deposited recently. I also noticed that some black hoses that snaked along the ravine also sprouted from the sediments as much as a metre or more below the surface. These had to be very young sedimentary deposits. But how young?

My travels up the road soon came to an end. Typhoon 19 had wreaked havoc on a section of the road. It seemed that water had traveled beneath the asphalt causing the road to sink in trenches and finally collapse at a bend in the road where the water could empty out into the ravine. A hundred metres or so up the road, the stream had wiped out a section of road.

On the way back down, further inspection of the mysterious sediments revealed a possible explanation. Green grass-like blades were sprouting from under roughly 50 cms of sediment. The grass was still alive but clearly had been buried. Nearby sat a large boulder with a cap of sedimentary deposits. That boulder could in no way keep a cap of sand and gravel on through a full summer/autumn season of thunderstorms and typhoons. The torrential rains would have washed it away. However, since Typhoon 19 there had been no heavy rainfalls of any significance, only usual rainy weather.

It was my deduction that either the dammed waters of the lake had flooded right back up the ravine or a clog of fallen logs had dammed the ravine. In either case, the ravine had filled up with raging muddy water charging down the mountainside causing an excessive amount of sediments to be deposited rapidly, covering hoses, grasses, and boulders. The river quickly cut through the layers since the typhoon but the sediments remained at the river banks, crumbling away little by little in the dry air even as I stood and examined them.

With that plan of exploration ended, I drove up into Kami Naguri, a small hamlet along the Iruma River, and stopped for a brief visit at a waterfall with no sign, only steps leading up to a Kanon statue overlooking the falls. For my final effort to find a place to set up my tripod, I went to the Shiraiwa Ravine to see how far I could get. I soon spotted a lovely gorge in a tributary stream. Red chert was exposed with alternating layers of light grey chert, and large boulders of limestone had fallen into the gorge from somewhere above. This place occupied me for the next hour or so.

At last I drove on to see how far the road went, but soon I came to yet another dead end. This time the reason was that a mine had formerly operated here. The concrete foundations of the structures were all the remained. In the distance, a bluff of limestone protruded from the tree-covered mountains. This was Shiraiwa – White Rock, the namesake of the ravine with its white boulders of limestone.

At last it was time to head back, but not before crossing over on more pass to see if there were any mountain views to be seen, which had thus far eluded me. I had a slight glimpse between the trees at Amamezasu Pass.


More photos from the chert gorge can be seen at Flickr.