By Michael

Previous post: Goldschmidt 2016 Yokohama: the conference (part I)

I was fortunate to attend two field trips during my visit to Japan, both before and after the conference itself.

Fuji-Hakone: Spring, forest, cave, and volcanoes around the area

We left Yokohama to the village of Oshino, northeast of Mt Fuji, the location of Oshino Hakkai: the eight springs. This area used to be a lake, lava flows from Mt Fuji covered the lake completely and it dried up. However, groundwater coming from Mt Fuji are still feeding some ponds and springs in the village.

Oshino Hakkai springs

The village itself was a classical “village made out of souvenir shops” place, and it was our first introduction to some of the unusual products Japan has to offer. Having had no breakfast that morning, I bought about 250 grams of dried squid and nibbled on it until we had lunch. This was also our first experience with the Japanese nature. I don’t know if it’s the season or just the way it is, but everything seemed greener in Japan. The grass, the trees and all other vegetation just seemed to be a brighter shinier green than I’m used to in Australia or my home country of Israel. Magical.

A typical Oshino scene (excl. souvenir shops)

Our next stop was lunch. We were served traditional Japanese food, meaning things that you don’t know what they are and there is no point in asking. You just eat it, no questions asked, and it’s delicious. Following that, we arrived at a CO₂ monitoring station: the Fuji Hokuroku Flux Observation Site. Hidden deep within a forest on the foothills of Mt Fuji (which we did not see by the way because of fog and clouds), this station is monitoring the CO₂ emissions from decomposing soil beneath the trees using boxes that trap the emitted CO₂ for several minutes and then analyse it:

Our local guide explaining the CO₂ gadget

There was also a tower equipped with all kinds of measurement instruments:

A 30-metre wobbly aluminium tower which we climbed all the way to the top

My Fuji is famous for the abundance of caves around it. Most of these are lava caves, formed as the top layer of a lava flow solidifies while the interior was still flowing. You can see familiar lava flow textures such as pahoehoe, but inside a cave:

Pahoehoe. In a cave.

What’s neat about lava flows, is that they occasionally flow over fallen trees. Once the trees decompose you end up with lava tubes, sometime large enough that you can crawl in them.

Lava tree mould in a lava cave with a mandatory (lava) shrine

We also visited an ice cave. While it wasn’t a cave made out ice but rather a cave that people used to hold ice because it’s so cold inside, it was still impressive. The special lighting in the cave only added to the dramatic effect.

Ice held in yet another lava cave

The next morning we had our first glimpse of Mt Fuji! It cleared up for about 10 minutes so we could see it from our hotel room.

Mount Fuji in all of its glory, and a rather impressive lenticular cloud above it

We started the long climb (by bus) to the mountain, to a place called the 5th station which is situated about 2400 metres high. It has a souvenir shop (obviously) and some other things to cater to people who starting climbing (by foot) from this position. From this spot you could clearly see why it was not possible to see Fuji from anywhere.

Clouds below. If you can’t see them, they can’t see you!

Looking up didn’t help either, as we couldn’t see the top because of clouds.

The top ~500 metres of the mountain obscured by clouds

On the one hand, we were slightly disappointed because the view wasn’t what we expected for. On the other hand, having clouds above and below gave this “floating island mountain” feeling which was still quite inspirational. We were scheduled to go and visit the Hoei crater, a crater that formed during Fuji’s last eruption about 300 years ago. Unfortunately, the winds were too strong and this bit of the excursion was cancelled (but see below).

We then took a short cruise on a pirate ship on Lake Ashi – one of the larger lakes in the area of Fuji.

Pirate ships. Japan, right?

We then visited the Onshi Hakone park, which promises magnificent views of Mount Fuji, as you can see in the following photograph:

Myself pointing to where Mount Fuji would be, if you could see it

Hakone Volcano and Hoei Crater trekking in Mt. Fuji

The second field trip was actually to the same area as before, the mountains of Fuji and Hakone, but the itinerary was slightly different. Our first stop was the Kanagawa Prefectural Museum of Natural History. I’ve been to several natural history museums in the past, and this one is definitely in the top of the list.

Overview of the Kanagawa Prefectural Natural History Museum

For a regional museum far away from any major city, it was impressive. It is not large and going though everything can take about one or two hours, but the exhibits were breath-taking. Usually in such museums, there are many “ok” specimens and several “amazing” specimens. In here, every single specimen was in a class of its own. They had huge dinosaur skeletons (replicas, btw), huge iron meteorite, a metre-wide single crystal of beryl, entire outcrops of geologically interesting localities put on display, and more.

A huge chunk of the Mundrabilla meteorite
This is just amazing

We left the museum, heading in the direction of a viewpoint which promised some of the best view of the Hakone volcano caldera with Mount Fuji in the background. However, the visibility was even worse than anything we had before and we got this instead:

Hakone caldera on the right, Mount Fuji on the right. At least that’s what they told us

Following this breathtaking view, we proceeded to the Hakone Sekisho, a historical checkpoint between Kyoto and Edo (aka Tokyo) which was used to control the movement of women and guns between the two cities.

Terrible visibility, but the fog makes everything seems magical

We had no idea because we couldn’t see it, but we were on the shore of Laki Ashi. We only realised it when we actually got to the water itself (by hearing it, not because we could see it). Once we got there we observed this scene, which made me chuckle and think “ah right, I know this place lol”

Pirate ships + fog = epic win

Back to geology now. Mount Fuji is probably the more spectacular volcanic feature of this area, but the nearby Hakone is bigger.

Mount Fuji and Hakone caldera (with Lake Ashi in it), 2x vertical exaggeration

We started our tour of the caldera by examining volcanic deposits on the caldera’s wall:

Interbedded ash fall deposits, lava flows and paleosoils. Added fog for dramatic effect

Hakone is rather an old volcano, in Japanese standards. The large eruptions that formed the caldera occurred tens to hundreds of thousands of years ago, and magmatic activity ceased almost 3000 years ago. Since then there were several minor phreatic eruptions, but nothing of interest for several hundres of years. Since then, the only activity was hydrothermal activity. The water were exploited for hot springs in the area and the famous Owakudani black eggs were produced and sold on site. All of this changed in 2015 when another phreatic eruption occurred, forcing the closure of the tourist and visitor centre located just above the hydrothermal vent field. We were granted special authorisation to enter the site and given personal protection equipment and monitors.

Our guide with H₂S and SO₂ monitors, and the author with helmet and respirator

To our surprise, we discovered that the black eggs were actually produced on site by workers who had no protection equipment!

We couldn’t actually see the hydrothermal vent field because of the fog, so in the meanwhile we had a stroll around the area, seeing some surreal sights.

A stream sourced from the hydrothermal water
Sulfur! Sulfur for everyone!

We could definitely hear and smell the hydrothermal vents, but we could only see them for very brief periods when the fog cleared a bit. Here’s one:

Eventually, the fog cleared enough to allow us to see the main hydrothermal vent. The video doesn’t do justice to it, but here it is anyway:

The trend of clearing fog continued throughout the trip. The visit to Hoei crater on Fuji was cancelled in the first field trip, but we sure got to see it now. The Hoei eruption was the last eruption on Fuji, starting late 1707 to early 1708. The eruption occurred on the flanks of Fuji, creating a huge crater.

Myself with the Hoei crater in the back. The eruption exposed some of the feeder dykes to the fissure vents that formed the flows that make Mount Fuji. Some of them are clearly visible above my right hand

We were also fortunate to observe rocks falling from the crater walls (and fortunate to stand elsewhere):

Leaving the mountain, we travelled to the extensive lava flows produced by the 864 Jogan eruption. The lava started flowing from a fissure vent on the flanks of Mount Fuji, as seen by this 3D model…

Lava flow highlighted in white

…which was then placed in a wider context provided by a geological map:

3D geological map of Mount Fuji, located in Fujisan museum

The lava flows reached one of the lakes surrounding Mount Fuji, splitting into two separate (but hydrologically connected) lakes. The location provides spectacular views of Mount Fuji, which we could actually see this time!

No fog and special thanks to whoever put that chair in there

The lava flow is covered by the Aokigahara forest, notorious for the unusually high number of suicides in it and legends of ghosts and spirits that haunt it. We had a brief stroll through the forest, but we were not looking for any supernatural activity. Instead, we entered a very impressive lava cave, one of the many that exist below the forest (this is a lava flow formation after all).

Our guide discussing lava flow textures on the cave walls
Guess the flow direction
On the way out of the cave

Our last stop (of scientific interest) for the field trip was a cross section of the Jogan lava flow, which features like the following are visible.

A mystery!

It wasn’t clear what this one. The local Japanese geologists suggested that these were tree moulds, but some of the American geologists who were participating in the trip as well insisted those are gas escape conduits which fragment the partly solidified lava flow (forgive me for forgetting what the term for that is).

That is all. I would like to thank again my supervisor John Mavrogenes and the Vice-Chancellor’s HDR Travel Grant for making all of this possible.