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.

IMG_3642

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

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