In Yogyakarta the city's ground was brought down by the volcano
Twenty-eight kilometres to the north stands a 2,930-metre cone that has erupted regularly since 1548. The plain where everyone lives is made of what has come down off it, and the rivers keep bringing more every rainy season.
A reasonable question on arriving is why so many people live so close to a thing like that. There are villages on the flank at seventeen hundred metres, with the crater above them.
The answer is underfoot. Living near the volcano is dangerous every few years; living far from it, on this island, means giving up the best agricultural soil in the world. People have been doing that arithmetic for centuries.
01 Twenty-eight kilometres away
The volcano is 2,930 metres today. I say today because the figure changes: in the 2010 eruptions the summit lost thirty-eight metres of height and the cone's characteristic outline was altered.
It is the country's most active volcano and has been erupting regularly since 1548. Because of its history of destructive episodes and the number of people living around it, it is on the international list of volcanoes considered to deserve priority monitoring.
And even so, there are villages on its flanks at seventeen hundred metres. How far you are from the crater is not measured in safety but in fertility: the closer you are, the better the soil and the more water, and the less margin when the cone wakes up.
02 The ash is the soil
What a volcano of this kind throws out is ash and fragmented rock rich in minerals. As it breaks down it produces deep, loose soils with a fertility ordinary tropical soils do not have, because in the tropics rain washes nutrients away as soon as they appear.
That is the key to the whole island. A young volcanic soil is renewed from above every time there is an eruption, so fertility is not exhausted by centuries of cultivation, which is exactly the opposite of what happens almost anywhere else in the wet tropics.
The result is visible from any road: terraced rice fields as far as you can see, two or three harvests a year and a very high population density. The plain is not just any flat ground; it is the fan of material the cone has been shedding for millennia.
03 The rivers are conveyor belts
What comes down off the cone does not arrive all at once. An eruption deposits enormous quantities of ash and loose rock on the flank, and that material sits there, with no cohesion, waiting for the next heavy rain.
When it really rains, all of it mobilises and comes down the ravines as a flow of mud and stones. In November 2010, a few days after the eruptions, intense rain generated flows of that kind which caused more damage than the ash itself.
That is why the channels leaving the volcano do not look like rivers but like wide tracks of grey sand. And that is why the sand is worked: the material is a first-order economic resource for the whole district, and the lorries carrying it up and down are part of the everyday landscape.
04 And to the south, the exact opposite
A few dozen kilometres to the southeast, the territory changes completely. A limestone region begins, with thousands of conical hills, known for that reason as the thousand mountains, recognised as a global geopark since 2015 and covering some 1,300 square kilometres.
There is no volcanic soil there and no terraced rice. There is limestone, dolines, closed valleys and, above all, no surface water: the rain sinks in and travels inside, through underground rivers and caves.
The contrast is textbook and you cross it in an hour's drive. To the north, fertile, densely populated land the volcano renews; to the south, a dry district poor in water that has historically had to solve its supply by drawing it from below.
05 From crater to ocean in no time
The whole administrative region covers 3,170 square kilometres: it is the country's second-smallest province-level entity, behind only the capital. And in that space fit an active volcano, an extremely dense agricultural plain, a karst region and a coast open to the Indian Ocean.
That compression is what makes it so easy to travel. From the city, which sits a little over a hundred metres up, you reach the volcano's flank or the coast in an hour or two, and the three units of the landscape can be seen on a single short trip.
It is worth knowing that the southern coast is not a swimming coast. It faces the open ocean directly, with heavy surf and currents, and works more as a viewpoint, a zone of cliffs and dark-sand beaches, than as a pool.
06 How to travel it
The useful way to organise yourself is in bands, north to south. The upper band is the volcano and its slopes; the middle one is the rice plain and the city; the lower one is the limestone hills and the coast. Each asks for half a day and all three are genuinely different.
The north is visited early, and not for the light: the cone is usually clear at first light and covered in cloud by mid-morning. If you came to see the volcano, the real window is at dawn, and in the rainy season it may not open for several days running.
And there is a way of looking that changes the trip. When you cross one of those wide grey-sand channels that look like quarries, notice that they all point to the same place. You are crossing the route by which the mountain has been moving to the plain, and the rice around you is the end product of that transport.
