Crash of Titans in our backyard: Looking stones in Togawa Park 秦野戸川公園

 

Let’s start our Tanzawa stone hunting from the backyard of suburban Kanagawa. This summer, we did a geological hunting session in the bank of Mizunashi River 水無川 for Tokawa Park 戸川公園. The place is popular with families in Hadano City 秦野市. When weather is right, the river does not have much flow, or even no water. Its reason is exactly from Plate Tectonics. Hadano City sits on Hadano Basin that is created by earth and sand accumulated from collapsing strata by crustal shortening. Coral seabeds and islands on Philippines Plate crinkled when the plate crushed with the Eurasian Plate. Inevitably lots of earth broke down along the active faults. Such sediment from the crash of Titans came down along the rivers of old Tanzawa and piled up in the area now called Hadano Basin. Then, volcanic ashes from Mt. Fuji and Hakone Mountains heaped on the crumbled soil. The result is a Basin on lots of active faults and more than 150m thick strata made of gravel, sand and volcanic ashes. The structure lets the water from Tanzawa mountains become groundwater, not river. The Hadano City has lots of famous springs here and there, but the visible waterflow on the ground is limited. Mizunashi, = “No Water” in Japanese, River does not have much regular flow, unless the underground water system reaches its limit due to torrential rain.

Tokawa Park in summer has
lots of families who enjoy breeze from the “water.”

Not much water for Mizunashi River

The Park itself is on the line of contact between Hadano Basin and “Oyama Subgroup 大山亜層群” for Tanzawa Group of geological feature 丹沢層群. We can regard the place as the point where the wrinkles of Philippine Plate start at the aboveground level. This birth story of Hadano tells Tokawa Park is a good place for collecting many kinds of rocks tumbling down from Tanzawa Mountains especially from the surface of shortened crust. In addition, the water systems of steep Tanzawa slopes carry rocks not only from Oyama Subgroup but also from a bit far Togatake and Susugaya Subgroups.

Mt. Oyama over there from Tokawa Park.
Rolling stones come this far from there, baby.

The sample map I made from the pebbles collected
from Tokawa Park and Yadoriki Stream.
The black arrow shows the point we did stone hunting.
The blue area is Oyama Subgroup,
and light green area is Togatake Subgroup.
The point itself is on the white area for Hadano Basin.

The birth order of these geolotical groups is, the oldest Togatake 塔ヶ岳亜層群, the middle Oyama, then the youngest Susugaya 煤ヶ谷亜層群 Subgroups. Togatake and Oyama Subgroup areas have rocks evolved from volcanic magma, mainly Andesites, that cooled rapidly near the surface. They were originally from very active underwater volcanoes so that the chemical reaction with the sea water lets them be colored green. In large rocks procured from the area we can often observe chunks of volcanic bomb trapped and fixed in the volcanic ashes by tectonic pressure. Some good and polished example is situated artfully in the slope of Tokawa Park when we come down from the visitor center to the river. Some are good for using as benches. 😉 Actually, Togatake Subgroup has a strong connection with Yadoriki area 寄. I tell you about it when we look the pebbles in Yadoriki Stream.

Mr. Kiyoshi Sudoh
of Kanagawa Earth Science Association
was our instructor for stone hunting.
This rock has volcanic bombs inside, like

Bomb trapped, or so called tuff breccia, of Tanzawa.
By the way, the rock itself looks perfect
 to have lunch on it, don’t you think?

The dry riverbed of Mizunashi River in Tokawa Park is wide. We walk gravelly fields for some time to reach to the water. Though, for stone hunters of Tanzawa’s tectonic journey it’s a fairly convenient space. We stroll there, even without rainboots, and pick up interesting pebbles. Each doubtlessly has marks of Crash of Titans. The stones here were formulated some 15 to 17 million years ago 240km offshore from the point as undersea volcanic tuff (and occasionally basalt). i.e. The rocks here were the memory of active volcanoes older than Mt. Fuji (; the last eruption was in 1707) or Hakone Mountains (; it’s still erupting). They were carried by the Philippines Plate and arrived here about 5 million years ago. Larger and thicker Eurasian Plate with heavy basalt and peridotite did not yield easily to the pressure from the Philippines Plate. Before came here, the uplift from the bottom of the ocean started to wrinkle at the point of Crush of Titans. Around Tokawa Park area the crustal shortening become ferocious on shore and many fault lines created crumbling rocks. Oh, yes. It’s in present tense. Philippines Plate continues advancing 10cm per year. Do the math. 1 million years produce steady and never- conceding 100km progress ... In the process, many kinds of chemical reactions occurred for tuff and basalt. These straight volcanic products turned into another kind of rocks with different textures and colors. The pebbles we find here underwent such transformations in the relatively shallow part of the Plate, compared with the other areas of Tanzawa. Next week, I’ll show off my catch here. 😊

The field for hunting

Lots of catch here!

At the entrance of Tokawa Park, there is Tanzawa Visitor Centre. The contact address is

Hadano Visitor Center for Tanzawa-Oyama Quasi-national Park
丹沢大山国定公園・自然公園秦野ビジターセンター

1513 Horiyamashita, Hadano, Kanagawa Prefecture, 259-1304
〒259-1304 秦野市堀山下1513

Phone: 0463-87-9300

https://www.kanagawa-park.or.jp/tanzawavc/

Pulse of the Planet: Picking up stones in Tanzawa, I

 

Tanzawa’s rock covered by, I think,
Riverina jigongshanensis, an endangered species
 … Really?

It is well-known that Tanzawa Mountains 丹沢 are one of the exemplar fields in Japan where we can observe Plate Tectonics. The main body of today’s Honshu Island was an edge of the Eurasian Continent where the North American Plate went under the Plate that the continent sit. More than 25 million years ago, the crush of these two titans ripped off the edge and created Sea of Japan / East Sea. By the power created by the collision of the Plates, the separated landmass that was still on the Eurasian Plate was cracked into 3 parts, the north, the center, and the south. The north rotated counterclockwise that became today’s Tohoku 東北 area. The south rotated clockwise and became today’s Kinki 近畿 and the southern area of Japanese archipelago. There are several theories why it was so, but in any case the center became a hinge for a double door of the north and south lands. It “stayed” as such with massive cave-in and volcanic activities. The rift became Fossa-magna area (; my post for October 5, 2018). Then about 20 million years ago, the center bedrock started to feel real pressure from the south by the Philippines Plate that had coral reefs and underwater volcanos. About 5-4 million years ago, these reefs and volcanoes reached the contact point with the remnants of Eurasian Continent, could not go under the Plate, and puckered there. The Tanzawa Mountains were born.

As a mass, mountains of Tanzawa are not so huge.
 But …

In this way, the surface of Philippines Plate was uplifted and became mountains. But even now beneath the mountains the Philippines Plate continues crawling down under the Eurasian Plate. After the first contact, the larger volcanic mass that was the beginning of Izu Peninsula 伊豆半島 followed bumping. The shock kept pressuring the original puckered coral reefs and volcanoes to go more inland and become taller. In addition, the energy of banging of two tectonic plates caused numerous terrestrial volcanic activity that spewed out new lava from the mantle. Among them were primitive Mt. Fuji, and mountains of Hakone area 箱根. Such volcanic products piled up over the raised undersea rocks from the south. Have you noticed something in this story? Yeah. These reefs and volcanoes were on the same Philippines Plate, but the plate is HUGE. It has many kinds of coral reefs and volcanoes since eternity. In addition, the original soil of Eurasian Continent and continuing volcanic eruptions can leave marks on the southern coral reefs and underwater volcanos. So, when we move around Tanzawa area which is not at all a large area, we can observe many kinds and histories of these activities in the Planet Earth’s evolution. That’s the reason why Tanzawa is good place to see tectonic movements.

This summer, I had a chance to observe such varieties in Tanzawa’s ground with experts. One theory for the origin of the name Tanzawa is, it was from old Korean that means Tan + Zawa = lots of small streams. Thanks to many small torrents running down steep rocky slopes of Tanzawa, it is easy to pick up many kinds of pebbles from riverbeds where people can safely approach. I made small specimen boxes of pebbles from 3 different points in Tanzawa. My 3 points were sides of (now familiar) Yadoriki やどりき沢, of Mizunashi River 水無川 in Togawa Park 戸川公園 (; my post for February 14, 2020), and of Nakagawa River 中川川 next to Nishi-Tanzawa Visitor Center 西丹沢ビジターセンター. I tell you they are all different. And they are more or less another side of a ridge each other. From next week, I will return there one by one. It’s really interesting that neighboring rivers can tell a different story of Planet Earth. Please stay tuned!

If you find environmental issues in Kanagawa Prefecture, please make a contact with

Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657

Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/

Update: 2026 Laboratory of Forest Art

 

CHIKADA Haruna

A week later for the originally planned opening party, the GROUP the Creation and Voice of the Woods held an opening party + art tour by the artists. This week I tell you about the artist’s comment for their own work. (The original note shown at each installation is my post for September 20).

1. encounter
ISHIKURO Kazuo

Ishikuro-san said originally he does not want to demolish his tower man for Hadano after their show, and decided to make him/her a neighbor of another tower man in the forest for the GROUP. He then found some forest story that goes on with the new situation. Could you feel that?

2. A Boat Made of White Oak Branches
KANAI Toshikazu

After working in this forest for years, Kanai-san said he became more familiar to the creatures in the forest, like that magnolia tree next to his boat, or the snakes gathering in a sunny open space created by his thinning to make room for another boat. His work becomes more and more the 21st century version of Noah’s Arc.

3. Where the Gaze Is Directed
CHIKADA Haruna

Chikada-san has changed her tack this year for her installation by not-using BB bullets. But she said in any way she did not want to shout loud about environmental destruction by survival gamers. She said she always wanted to nudge the spectators to move the point of view from a familiar “me” to that of the entire environment. For that, mirror is a useful tool. In this year’s installation, mirrors reflect the canopy of the forest above AND you who look her work. Finding yourself on the surface of fallen tree, what would you think?

4. relationship like this in the cockpit.
ASADA

ASADA-san plans to add another crew next year for the cockpit of spaceship earth. For more detail of this growing population of spaceship, please check the movie from the QR code below.

5. Here
YOSHIKAWA Youichiro

According to Yoshikawa-san, to retrieve the feature of “ownerless garden” of dwarf lilyturfs it took almost a month of weeding sasa bamboos and brackens. In addition, several cherry trees surrounding his “garden” fell during these several months. He speculated the aging of the forest was rapidly progressing. His toil for maintaining “ownerless garden” itself is becoming more and more a creative process in a fast-moving environment. Let us see how the things turn out …

6. Layer 2209 or 2232
KIGA Youko

2209 and 2232 are frequency these wind chimes emit. For Kiga-san using the space in this forest is very free. Her creativity can fly without enclosing walls. Her intention was about the free “space” in the forest, but I noticed the sound of chimes can waft out from the forest to the commuter road running along the forest. Her chimes are expanding beyond the forest.

7. BOND+ (connecting logs +)
HARADA Akatsuki

Harada-san noticed by working this project for several years by now, the originally “all-sturdy” log structure has begun to show variegated development regarding its decay. Some parts have so-so puffy logs, while another part is forever solid. He situated on the top of the structure the twigs harvested from the forest, painted them white and connected them together. It looks like people holding hands and support the entire building even if a part of it is decaying. That’s a sort of symbolism for something …

8. Pergola Gallery

When the GROUP started 20 years ago, the members of the secretariat were art lovers who responded to the help-wanted appeal for art show in a forest. Many already had created their art works, if not professionally. Since then, they contributed to the show little by little that left their installations in the forest as the artists for the annual show. Some brought in the works made by users of special needs center in Yokohama. The others created the installations with kids from local after-school childcare centers. And the other found the thinned oaks by the artists attractive to make his own art work in the forest. This part of the forest is for the secretariat people. I found the Gallery is full of fun! Please enjoy.

The closing for this year’s show is on October 18. There again will be an Art Tour from 11:00. After the bento-lunch (RSVP from email below), they will have a concert by Thomassons + Akaciq in the forest. For both parties, you can bring your own lunch. It is free of charge just for attending the parties. There will be a small “Marche” on the closing day to raise funds for their activity. In addition, on October 4th from 11:00 they specially arrange an Art Tour for kids and their guardians. This event has a limited seat for 10 kids and it will cost 500 yen per kid (for insurance charge). RSVP.

2026 the Laboratory of Forest Art is held during September 20 – October 18 in the same forest of the previous years. Since there is no parking, a recommended access to the Forest is by bus. The most convenient transportation is a bus ride to Yokohama Zoorasia, from JR Nakayama 中山 Station, Sotetsu Tsurugamine 鶴ヶ峰 Station, or Sotetsu Mitsukyo 三ツ境 Station. Get off the bus at the North Gate of Zoorasia that is the closest to the art exhibition entrance. When you leave the terminal stop of Zoorasia North Gate, go back a bit along the bus road, and on your left is the sign for the GROUP. From there enter the forest. The road is a relatively wide walking promenade. Soon you can see a big banner over there saying “the Creation and Voice of the Woods 創造と森の声.”

When you find a problem in the site introduced in this post, the best contact address will be GROUP the Creation and Voice of the Woods.

https://morilab.amebaownd.com/
e-mail: morinokoe7@yahoo.co.jp

The city office which is in charge of this forest is

Zoo Division 動物園課
Yokohama Municipal Government Green Environment Bureau 横浜市みどり創造局

Phone: 045-671-4124
FAX：045-550-4650
email: mk-satoyama-garden@city.yokohama.jp

In Search for Lost Crickets: endangered Euscyrtus japonicus

 

Euscyrtus japonicus is in the family of Gryllidae, aka crickets. It’s tiny. It has 1-1.2cm of body length. Its legs are very slender. Their wings are not sturdy enough to fly around. So, they are not good at moving. It doesn't sing, although it’s a cricket. Probably the most prominent feature of the bug is female ovipositor, the organ to lay eggs, which has almost the same length as its body. Otherwise, it’s low-key. Having said that, it’s picky for its meal. Its diet comes only from long leaves of grass families. They are not good at exploring new worlds for food with their weak wings and legs. When they have home, they make a large colony in the same bush of grass with their fellow crickets.

People from Yokohama Environmental Science Research Institute, a watch dog in charge of environmental pollution in the city, have found the bug VERY rare in the city. For that matter, in the entire Kanagawa Prefecture, meeting them is getting rarer and rarer. In the recent Red List for insects and spiders in Kanagawa (my post on September 6, 2026), they are categorized as VU = vulnerable. It’s same in Tokyo, Saitama, and Chiba. All of these prefectures including Kanagawa give Euscyrtus Japonicus the endangered status. There were lots of bitten leaves, for sure. But. Some had bite marks at its tip. The others were eaten from its edge. Unfortunately, no leaves with holes only in the middle.

Instead of crickets,
brown winged planthopper
(Pochazia shantungensis)
 is ubiquitous these days
in grass of Yokohama …
They are registered
“invasive species
that harm orchards”
 by the Plant Protection Section of
Ministry of Agriculture,
Forestry and Fisheries of Japan.

Er, well, it sounds demanding but at least around Yokohama, it seems to me grasses are abundant so the insect may not have hard times for survival. I decided to do a mini search for them in the wide expanse of grass family along the bank of Tsurumi River. The bugs leave very characteristic feeding signs if they are there. They eat only the middle of slender leaves of grass. They avoid apex, margin, and of course midvein. After their meal, the grass leaves have lots of elongated holes in both sides of midvein. Since they live en masse, the leaves of their grass “town” are supposed to have lots of holes. It must be easy to find them ... Result? Nah.

It seems to me
there are lots of meal here for the crickets.

This young Patanga japonica
has surely different table manners
 from Euscyrtus japonicus.

I simply wondered. Why? With such a lot of leaves, the cricket must be able to eat a lot. One speculation could be their be-loved field of grass which can undergo frequent disturbances in big cities of boiling planet. Take the bank of Tsurumi River. Thanks to this changing climate, sudden torrential rain over our concreted neighborhood pours water directly into the River. The grass on the bank will be inundated at once. Even if the flood is for a very short period of time, it’s enough for tiny crickets to be washed over, and extinct. Or flood control constructions. The bank receives heavy mowing at least once a year to stop overflowing into human area. Yeah, grass will come back soon but meanwhile what to eat for these picky crickets?

It’s a hard life for this inconspicuous insect. What will happen to them? I decided to search for holes when there is abundant grass in our neighborhood. The scenery looked familiar and permanent. But from Euscyrtus japonicus’ point of view, it’s turbulent surroundings. I recalled the quiet fury of these bugs’ nerds in the symposium. “Beautifully conserved nature? Look, who’s talking!?”

If you find environmental issues in Kanagawa Prefecture, please make a contact with

Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121
〒243－0121　厚木市七沢657

Phone: 046-248-0323

You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/

Rain … for 2026 Laboratory of Forest Art

 

I secretly doubt Mr. Ishiyama, the coordinator for the GROUP the Creation and Voice of the Woods, is a rainmaker. 2026 Laboratory of Forest Art was supposed to have an opening party on September 20, 2026 (i.e. today). From 19th or so, Typhoon Dujuan has begun bringing Yokohama rain and wind in honest. The estimate almost hourly changes the speed of the storm. Now forecasters say the heaviest rain will come Yokohama tomorrow evening. Yet, it is already raining heavily now. Inevitably the opening party was postponed for next week. Still, artists have installed their work in the forest. So, today I will tell you this years’ Forest Lab installations. At the entrance, the group gives us a reference map to visit artworks. I proceed according to the numbers they allocate each. The title of this year’s show is “Forest, From Now.”

1. encounter

ISHIKURO Kazuo

“A tower man born last year here have met another tower man born in Hadano this May. The same work would look different according to the place and the way for them to be shown. This year please be a tower man with both guys.”

2. A Boat Made of White Oak Branches

KANAI Toshikazu

“For these six years, I’m caring a seedling of Magnolia obovate here. I was concerned with a white oak standing next to the baby Magnolia that would take over the place instead of my tree. This year I cut the oak. In the end managing forest means whatever we do with our egotism. I cleared logs and branches with guilty feelings and resignation. Then, suddenly I noticed suckers were already coming from the stump of fell-down tree. When we clear the forest and let the sunlight come in, izzards visit the place for warming up. New plants will shoot up after the oak. The Boat here may already be Noah’s Ark.”

Below, Kanai-san’s last years installation. Together, they started to form a fleet of Noah’s Ark.

3. Where the Gaze Is Directed

CHIKADA Haruna

“I thought I was looking. I realize I did not look.

I thought I was looking this way. You say you look the same thing in another way.

In the forest, surely it would.”

This year Chikada-san takes another approach to the forest. She has not used BBs. She collected them from the forest floor and quietly fumed survival gamers polluting the forest with tiny plastic garbage. She said this year the feeling is not much since the level of new pollution is subsided. Yet … By the way, here work will be completed when the blue cover over each panel is removed and the trunk is covered by flexible mirror. I think she will finish her work after the typhoon is gone.

4. relationship like this in the cockpit.

ASADA

“Last year, a meandering creature reached the cockpit in the forest and realized it is a member of the starship Earth. It took a rest here in the cockpit. This year another creature arrived the cockpit, and they begin new relationship. It is an eternal cycle of birth, mate, feel, think, and decay. It is the energy to move Earth.

The movie version of the story can be seen from here.

5. Here

YOSHIKAWA Youichiro

“In 2017, I made here a large circle and snakely strolling path by replanting mondo grasses from another places in the forest. A year passes from my previous “gardening”, and all the work are covered by sasa-bamboos and ferns. This year, I’ve again done my “gardening” by mowing the covers to make the mondo grasses reappear. I feel happy as I am digging up my last year’s work painted on earth. This year, I build a mark to point my creation.”

Yoshikawa-san is retrieving last year’s work. He said several large trees, including Cerasus jamasakura, surrounding his “garden” fell and the spread of sasa-bamboos are phenomenal this year. To recover the last year’s design of his “garden” he commuted the forest for days. This year’s wheel is heavier, it seems to me. Please try.

6. Layer 2209 or 2232

KIGA Youko

“Standing here, have you heard wind chimes?

Mother nature let the song come out.

It’s beyond our control.

If you can hear it now, you’re lucky.

Otherwise, that’s that.

Fickle and blind.

7. BOND+ (connecting logs +)

HARADA Akatsuki

“Heartwood of thinned trees from the forest was sturdy. Since 2023, I’m connecting these logs with iron-reinforcing bars. Bars are clamps, aka bonds. I hooked up the heartwoods with bonds and built up a circle structure. The work becomes very robust. This year, I added future form of us on top of the construction.”

8. We Made this Pergola Gallery Together

This part of the show is created by coordinating members of the Group, local kids, and the people from the nearby institution for people of intellectual disabilities. Many authors here are amateurs and simply enjoy the creation. It was fun to immerse myself in such environment!

They postponed the opening party for September 27, starting 11:00 AM with “Art Tour” guided by the artists. After roughly 1.5 hours of slow walk in the forest, there will be lunch and art discussion with the artists. If you like to share bento-lunch with them, please email

morinokoe7@yahoo.co.jp

to reserve the purchase of bento. English email is OK. The closing is on October 18. There again will be an Art Tour from 11:00. After the bento-lunch (RSVP), they will have a concert by Thomassons + Akaciq in the forest. For both parties, you can bring your own lunch. It is free of charge just for attending the parties. There will be a small “marche” on these party days to raise funds for their activity. In addition, on October 4th from 11:00 they specially arrange an Art Tour for kids and their guardians. This event has a limited seat for 10 kids and it will cost 500 yen per kid (for insurance charge). RSVP.

2026 the Laboratory of Forest Art is held during September 20 – October 18 in the same forest of the previous years. Since there is no parking, a recommended access to the Forest is by bus. The most convenient transportation is a bus ride to Yokohama Zoorasia, from JR Nakayama 中山 Station, Sotetsu Tsurugamine 鶴ヶ峰 Station, or Sotetsu Mitsukyo 三ツ境 Station. Get off the bus at the North Gate of Zoorasia that is the closest to the art exhibition entrance. When you leave the terminal stop of Zoorasia North Gate, go back a bit along the bus road, and on your left is the sign for the GROUP. From there enter the forest. The road is a relatively wide walking promenade. Soon you can see a big banner over there saying “the Creation and Voice of the Woods 創造と森の声.”

When you find a problem in the site introduced in this post, the best contact address will be GROUP the Creation and Voice of the Woods.

https://morilab.amebaownd.com/

e-mail: morinokoe7@yahoo.co.jp

The city office which is in charge of this forest is

Zoo Division
動物園課
Yokohama Municipal Government Green Environment Bureau
横浜市みどり創造局

Phone: 045-671-4124
FAX：045-550-4650

email: mk-satoyama-garden@city.yokohama.jp