■Mt.　Aso
Visitors to the southern island of Kyushu won’t want to miss Mt. Aso, one of Japan’s most spectacular sights.  Mt. Aso is by some accounts the largest active volcanic caldera in the world, with a circumference of about 75 miles (120 kilometers) and a diameter of nearly 17 miles (27 kilometers) at its widest point.

But if you’re picturing a seething sea of magma you couldn’t be more wrong.  Instead, the crater is a green, rolling landscape laced with roads and even rail, housing several towns.  The largest of these, Aso, has a population of over 30,000.  Large alpine pastures are used to graze cattle and horses, and the steep, verdant slopes of the caldera rim rise in the distance, with a large gap in the western wall where an ancient lake drained into the plain below.

Mt. Aso is a somma volcano, which occurs when an active cone (or cones) forms inside an older caldera.  Aso’s caldera was formed around 90,000 years ago in a colossal volcanic event that released material roughly equivalent to the mass of Mt. Fuji.  Following this collapse, five cones formed in the caldera, only one of which is presently active.  That cone, called Naka-dake, is one of the area’s principal attractions.  From its base, either a twenty-minute walk or a ropeway will take you to the crater’s rim, where you gaze down into a roiling mass of steam and twisted stone, with a grim lake appearing through breaks in the vapor.

As countless visitors will attest, Mt. Aso should definitely be on your itinerary if you’re planning a trip to Kyushu.

■The Kusasenri plateau is one of the most picturesque areas within Mt. Aso’s enormous caldera.  Spreading about a kilometer across, this green bowl slopes very gently down to a beautiful little crater lake.  The meadow is a popular stop for tour buses, but if you’re lucky with your timing you may have it mostly to yourself for a short while.  For much of the year you can ride horseback around the meadow, fun if you’re traveling with older children.  The Aso Volcano Museum on the edge of the plateau is interesting, showing the range of volcanic activity throughout the Japanese archipelago and even offering a glimpse into the heart of nearby Nakadake, the only active crater on Mt. Aso.  It’s also possible to hike to Nakadake from here, a walk that should take most people a little over an hour and provide a more interesting way to see the meadow and the approach to Nakadake than simply driving up to the ropeway station.

■Nakadake
Of the five peaks found within Aso’s caldera, Nakadake is the only one that is presently active, with occasional ash eruptions.  In fact, if you go to the summit you’ll find concrete bunkers to shelter in, should the vent begin lobbing superheated stones into the air.  A number of bunkers partially buried during an earlier eruption are also visible.

The top can be reached either by car along a toll-road, by ropeway, or on foot.  The active portion of the crater is in the north end, and is off limits, but you can walk around the southern portion of the mountain, taking in the eerie, blasted landscape.  The cauldron produces a more or less steady stream of gases and vapors, some of which are poisonous.  If activity within the cauldron is especially intense, Nakadake may be closed to the public.  Visitors with respiratory difficulties are cautioned to look for entertainment elsewhere, with gas levels reaching potentially hazardous levels even on days when the crater is open.

>>Access
Kumamoto IC===(40 min. by car)====Kusasenri ====(5 min. by car)====Nakadake

-Matt Mangham

>>Hotels and Ryokans close to Mt. Aso