Mount Aso and me: How I risked death on a Japanese volcano

By now, we surely all know that Tokyo’s great for hiking, but what to do when you’ve scaled all the peaks in the capital’s foothills, quaffed all the beer for sale on their slopes and run the Chuo-sen trains ragged in your muddy boots?

Tired of the same old local trails, I decided to look a little farther afield and found myself fascinated with 1,592-meter Mount Aso in central Kyushu.

With jagged peaks, volcanic boulders, and steep inclines, it’s about as hardcore a hike as you’re going to get without having to rope up.

Mount Aso: Our idea of a fun day out ... in hell.

Oh, and did I mention it’s the largest active volcano in Japan? Double hardcore.

Charm points

The aspects that struck me about Aso were the contrasts. Barren desert-like landscapes and grassy fields. Black ash and beautiful blue skies. Massive boulders and sand fields. Fresh breezes and heat waves.

And, most importantly, life and death.

Is there life on Mars? Sometimes it seems more likely than there being any in Aso's more barren parts.

This is no exaggeration. Mount Aso is very much alive. It is also a taker of life. Numerous calderas emit constant puffs of volcanic gas that can take your breath away -- permanently, if you happen to be in the wrong area at the wrong time.

Sounds like my idea of a vacation: beauty and the beast.

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Keeping up the metaphor, I grabbed my husband, Matt, and the two of us made our way to Haneda Airport for the two-hour flight to Kumamoto and the hour-long drive to the trailhead.

What we call Mount Aso in the (English, naturally) singular actually consists of five mountain peaks. Mounts Taka and Naka are the tallest and most famous, but what many visitors don’t realize is that they sit inside a massive mega-caldera created some 300,000 years ago.

Enter the Dragon: the East Crater Lookout trail runs along the ridge of the caldera.

Today, half a million people, and farms and rice fields, sit inside the rim of a giant valley created by an eruption so enormous that its ash can be found more than 1,000 kilometers away in Hokkaido.

My favorite: Sensuikyo Ridge. The path is an ancient lava flow with breathtaking views from top to bottom. Navigating it requires a lot of balancing work and occasional scrambles on hands and knees.

It leads to Mount Taka, the peak, which affords unobstructed 360-degree views of the entire Aso area.

Life on Mars

Next we hiked over a saddleback to Mount Naka, which overlooks the largest active caldera in Japan.

The scenery drastically changed as we approached the peak. The lush, green vistas from Mount Taka quickly gave way to something rocky, alien, Martian -- ash and barrens, violently streaked with yellows, oranges, and other earth-tones, evidence of powerful forces at work beneath our feet.

Far below, a white cloud drifted up from the emerald waters filling the one active caldera, wafting up and disappearing into the blue sky like ... well ... poisonous hydrogen sulfide.

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It is just as we’re contemplating the beautiful, if potentially deadly, gases that we hear an alarm issuing from the visitor’s center on the other side of the rim.

“Warning. Concentrations of gases harmful to human life detected. Please evacuate Zone B-1 in an orderly manner. Warning. Concentrations of gases ...”

“That’s ... interesting,” says my husband. “Are we in trouble?”

“The thing is,” I tell him, “there’s no official measurement of levels here on the east side, so hikers like us have to use our own ‘guesstimates.’”

“I’m not sure that answers my question.”

The guesstimate is based on how thickly the sulfur smell is hanging in the air. Low tech, but hey -- it seems OK.

To be on the safe side, we make the decision to take a quicker route down than the one we took up. We paid attention to the wind direction coming off the caldera, put on a pair of gauze masks, and hoped for the best.

Still kicking

From Mount Naka, we hiked over to the East Crater Lookout, descending via an old concrete trail back down to the parking lot. Not only did this make a more efficient loop than having to retrace the same path back down, being paved it was easier going than Sensuikyo ridge.

Hold your breath -- gases rise from the most active caldera.

But it also follows the lip of the active caldera. Great for the eyes. Not great for the lungs if Mount Aso decides it has a bad case of gas that day.

Arriving back at the car an hour and a half later, we were finally able to breathe sulfur-free sighs of relief. But, no regrets.

Even though hiking an active volcano comes with its own unique concerns, it isn’t every day you get to gaze into a live dragon’s mouth.