The inner world of Mt Asama

Investigating the crater’s secrets with some help from the academicians

Our luck was out. We’d left Tokyo in the early hours, hiked over the old volcano’s wall and now, around noon, we stood atop Mt Asama’s curving summit ridge. Sulphurous steam roiled at our feet before heaving its way up into the sky; today, there would be no gazing, spellbound, into the nether world of the crater floor, corralled by its ring of scorched and blasted cliffs.

What is it about Mt Asama? As a climb, it has little merit. Yet that crater has pulling power. It was Asama that Kojima Usui, the founder of the Japanese Alpine Club, chose for his first excursion over 2,000 metres. That was in 1899. A few years later, the adventure photographer Herbert Ponting brought along a step-ladder so that he could peer just a mite further into the crater. And, as we have seen, he nearly paid for his temerity with his life.

Nor can the savants keep away. Scientific observations at Asama started in 1910, seven years after Ponting’s visit, “motivated by eruptions and a seismic swarm”. In fact, this was one of the earliest seismic observations made of an active volcano. Since our own visit in the mid-1990s, a quiet period, Asama has hotted up. In 2009, a light ash-fall drifted as far as Tokyo. A few months later, cameras on the crater rim caught the opening of a new vent in the crater floor.

For the academicians, this activity has been an incitement. Starting with “only six seismometers” just before the turn of the century, they’ve festooned the mountain and surrounding areas with 30 seismometers, 15 GPS sites, 10 tiltmeters, nine microphones, and two cosmic muon detectors.

The kit has helped the geologists put together a clearer picture of Asama’s underworld. They can now tell you, at least tentatively, what you might find if you ventured down into the crater – that is, provided you could stand the noxious gases and the 200°C heat there – and if, like Professor Lidenbrock in Journey to the Centre of the Earth, you then decided to investigate that mysterious vent in the crater floor.

Jules Verne would certainly get a run for his money from this journey. Once you’d dug or drilled a way through the congealed lava that plugs the vent, you’d find yourself in a “conduit” about fifty metres across, twisting downwards into the darkness. You’d need a long abseil rope or ladder: the shaft drops more or less vertically for three kilometres – the height of the mountain plus a further kilometre into the depths of Japan’s basement rocks.

At last, the vertical shaft debouches into the ceiling of a vast chamber. If the view were not blocked by a sluggish volume of semi-molten rock, you’d see it opening out into a vast cavern – somewhat like one of those Cyclopean storm-sewers in Tokyo, yet hundreds of times larger, and rather higher than it is wide.

Now you get the picture – the upwelling lava has forced the country rocks aside for several kilometres. You follow this dyke – a giant underground ravine – for several kilometres, more or less horizontally.

It takes you westwards and slightly north of Asama’s summit, out under the old Kurofu crater rim. Strange, you ponder: wherever the lava that feeds Asama’s eruptions comes from, it seems not to rise from directly beneath the mountain.

Five or so kilometres northwest of Asama’s summit, the rugged walls of the dyke start to close in. And there you start to sense far below you – another few kilometres down – a steady, intense reverberation of dull-red heat.

So this is where the lava comes from – a vast magma chamber, offset to Asama’s west, and doming out some four or five kilometres below sea level. From there, the molten slurries force their way up periodically into the dyke, and thence to the surface. Well, we’re not going down any further – it’s hot as hell here in the dyke, so you’ll have to imagine conditions in the magma chamber for yourself…

Up on the summit of Asama, at 2,568 metres above sea level, the summer breeze blew cool. Clouds had started to drift in too, mingling as they lofted over the rim with the steam from the crater. It was time to go. We found the path and followed its slant across the black-ribbed slope.

At the foot of the cinder cone, we met a troupe of Thai girls, in sandals and T-shirts, on their day off from some nearby bar or factory. We could hear their laughter for a long time, floating down from the summit, while we climbed the J-Band back towards the outer world. Perhaps they’d been rewarded with a better view.

Reference

Y Aoki, M Takeo, T Ohminato, Y Nagaoka and K Nishida: Magma pathway and its structural controls of Asama Volcano, Japan - image of vent and chart above from this paper.

And see Tsubakuro's blog for a more recent visit to Mt Asama - complete with a spectacular image of the new "live" vent.

Fires of Tartarus

A close call for two foreign visitors on Mt Asama

What is it about Mt Asama? On a fine day in October 1903, while climbing the volcano's lower slopes, the two Englishmen had seen “a cyclopean pillar of writhing smoke and vapour pouring up into the vault of heaven”. This should have reinforced the warnings they'd already heard and dismissed. Yet still they pressed on – something drew them – until they stood on the very lip of the fuming crater.

SHOOTING THE VOLCANO IN OLD JAPAN -- Photographer and Coolie Living Dangerously, a photo by Okinawa Soba on Flickr.

Or perhaps Asama's attractive powers weren't so mysterious. Herbert Ponting - the photographer who would later accompany Captain Scott on his last expedition - was in Japan to write a travel book and take pictures, the more spectacular the better. He'd already visited Aso-san in Kyushu, but that gigantic crater had proved disappointingly mild-mannered. So he had high hopes of Asama... Here Ponting takes up the story in his own words:

We saw an immense pit, six hundred feet or more across, and almost perfectly round, with perpendicular walls towering up from the bottom, five hundred feet or so below. These walls were burnt, and scorched, and stained with fire to every colour of the spectrum, and from a myriad cracks and crannies sulphurous jets of steam hissed out, each contributing its quota to the filmy vapours that rose out of the abyss from the fires of Tartarus below. Through the thin steam the entire crater floor was visible. It was a huge solfatara, with numerous holes from which molten matter was spurting, and red-hot lava pools which now and then were licked by little tongues of flame.

The noise of the place was truly infernal. There is no other sound on earth that can be likened to the sticky, sputtering buzz of a volcano. It is fearful to listen to — this vibrating, throbbing, pulsating din of ceaseless, steady boiling. The thing seemed to be fermenting with suppressed rage, and one half expected that any moment it would burst open and loose the furies it could scarce restrain …

Whilst absorbed in the contemplation of these beautiful surroundings, and the wondrous red and purple colouring of an ancient broken crater on the mountain's western side, the time sped swiftly on, and it was not until 3 o'clock that we prepared to leave. Our coolies went on ahead, but Hurley and I stopped a few moments for a last look at the crater, from which we found it hard to tear ourselves away. As we stood on the brink of the diabolical abyss there was a crash like a thunder-clap, and the earth seemed to split before us as the bed of the crater parted asunder and burst upwards, throwing thousands of tons of rock against the walls. For a moment or two the noise was like the din of battle. Masses of rock were hurled against the cliffs and shivered to fragments with reports like exploding shells, and showers of stones, whistling past us, shot many hundreds of feet into the air.

It all occurred so quickly that I cannot recall all my sensations, but remember thinking that my last moment had surely come. It seemed we must inevitably be struck by the falling stones. My first impulse was to seek safety in flight; but after running a few paces it occurred to me that the stones were just as likely to hit me running as standing still. Hurley had also started to run, but was evidently seized with the same conviction, for, without a word, he stopped too, and we both waited for our fate. Just then the smoke, which rose from the crater immediately after the explosion, swept in a great cloud above us, so that we could not see the flying stones, or form any idea where they were likely to fall. I shall not soon forget those moments, as we gazed upwards, with arms involuntarily held tightly over our heads for protection, waiting for the descending missiles to drop out of the smoke-cloud and annihilate us.

And then the stones came clattering down — sticking, with sharp thuds, deep into the ash. By good luck the main force of the explosion was directed slightly to the east, and on that side of the crater most of them fell. We were on the southern rim, and in our vicinity only a sprinkling dropped compared with the hail of rock that must have fallen a little farther off.

No sooner, however, were we safely delivered from Scylla than the perils of Charybdis were upon us. The smoke that was belching from the crater's mouth now enveloped us, and in a moment we were choking and almost asphyxiated with the sulphurous fumes. It was impossible to breathe, as, with hands tightly pressed over our mouths and nostrils, we blindly ran through the smoke for air. Fortune again was with us. In less than twenty paces we emerged suddenly from the chaos into brilliant sunlight, and staggered well out into safety before we fell upon the ground, gasping and filling our lungs to their fullest extent with great draughts of sweet pure air. It was a happy thing for us that the strong breeze which was now blowing was coming from the south ; thus the smoke was blown away from our side across the crater. Had it been blowing from the north we should have been unable to escape from the suffocating fumes.

This column of smoke was a thing of most awesome beauty, and held us fairly spell-bound. It belched up into the air in great, black rolls, which were emitted with such force and quantity that they were pushed far back into the teeth of the wind, and several times we had to retire still farther off as they bellied out towards us. It rose to the heavens in immense, writhing convolutions, and from the centre of the mass huge billows of snow-white steam puffed out, and bulged against the smoke, seeming to fight with it for mastery. But as white and black rose higher and higher in turn they mingled with each other, and soared up to the skies in a gradually diffusing pillar of grey which was tilted northwards by the wind and borne off rapidly into the clouds above.

References

Herbert Ponting, In Lotus-Land Japan (1910)

Many thanks to Okinawa Soba for posting Ponting’s dramatic photo on flickr, whence it is linked here. And to Tom Bouquet, volcanologist and educator, for originally posting this photo on his own (alas, dormant) Japan volcano blog. I hope he won’t mind me duplicating his efforts.