Cone karst in Gunung Sewu is a landscape of many rounded limestone hills, each separated from its neighbours by closed depressions. The hills are the defining feature of the region’s surface, and they are the reason Gunung Sewu is so often used to explain this landform type. This page covers how cone karst differs from tower karst, what the hills are made of and how they are shaped, why the total number of hills is hard to pin down, and what the landscape means for the people who live on it.
Cone karst and tower karst are different landforms
The two terms are often used together, but they describe different things. Cone karst is made of numerous rounded, conical or dome-shaped hills, with closed depressions between them. Tower karst is made of steep, isolated towers of limestone, often with near-vertical sides, standing on a flat plain or basin. Tower karst is best known from southern China and northern Vietnam, where towers rise sharply out of the surrounding ground. Cone karst is a different kind of terrain, and it can share the landscape with ordinary plains, valleys, flat-floored basins, slopes and river terraces.
The distinction is useful because it points to different settings. Tower karst is typically found on plains or basins, where the limestone stands above a flat surface. Cone karst is found across a wider range of ground, including areas where the land has risen over time and water has worked on the rock for a long period. That is one reason the two are usually treated as separate forms rather than as two shapes on a single scale.
On the ground, the difference is one of spacing and steepness. Tower karst tends to have sharper outlines and steeper walls, with clear flat ground between the towers. Cone karst tends to have a more continuous field of hills, where the slope of one hill runs into the depression beside the next. The eye sees a sea of rounded tops rather than a set of separate spires.
What the Gunung Sewu hills look like
Gunung Sewu is one of the best-known places to see cone karst in Indonesia, and its hills are the kind of rounded, numerous forms that give the landform its name. The region sits on the southern coast of Java, and the hills run across Gunungkidul, with parts of the area in Wonogiri and Pacitan. The area spans Yogyakarta, Central Java and East Java, so a hill in one district may sit close to a hill in another province.
The shape of each hill depends on the rock it is made of and on how water has worked on it. Limestone dissolves slowly in water that is slightly acidic, and rain picks up carbon dioxide from the air and from soil as it falls. Water moving through cracks and pores enlarges them over time, and the rock is removed from the surface in the process. The result is a surface of rounded forms rather than flat ground cut by rivers.
Because the hills are shaped by dissolution rather than by stream erosion, the valleys between them do not usually cut deep channels. Water sinks into the ground rather than running off across the hills, so the landscape looks dry even in places where a great deal of rain falls. Walking across the hills, you may notice that a valley floor is a closed hollow rather than the start of a river.
How many hills there are in Gunung Sewu
The number of hills in Gunung Sewu is not settled. The commonly quoted total is roughly 40,000 cone hills, but the figure depends on how a hill is defined, what is counted as a separate hill, and what is treated as one shape broken into parts. The region is large and crosses several administrative boundaries, so a survey that stops at a district line will miss hills on the other side. A count made from imagery covers only what can be seen, which can be affected by vegetation and haze.
If you want a sense of scale without relying on one figure, count the hills along a single road or ridge. The pattern repeats so consistently that a short walk gives a reliable impression of how dense the hills are. Treat any single figure for the whole region as an approximate guide rather than a precise total.
Why the hills matter to the water system
The hills and the water are part of the same process. The same water that carves the hills also carves passages underground, and the underground water is the main way the landscape drains. Cave systems are part of the same story as the hill shapes. A visit to Goa Jomblang shows the vertical side of the system, where a cave is entered from above through an opening in the limestone, and the route of the underground water is covered on the page about Gua Bribin: location, access and what to expect.
Because the water runs underground, a visitor cannot judge the drainage from the surface alone. A dry gully may carry water in the next heavy rain, and a spring in the lowlands may draw on water that entered the hills above a different village. This is one reason the landscape is difficult to read from a road, even though the hills are easy to see.
Why the shape of a karst hill tells you about the rock
The shape of a hill is a record of the rock underneath it. Harder rock resists dissolution and keeps its outline, while more porous rock lets water in and wears away faster. Where the same limestone changes character over a short distance, the hills change shape with it. Two hills of similar height can therefore look different, depending on how their rock is fractured and how easily water can enter it.
For a visitor, the variety is easiest to see from a high point. A ridge or viewpoint lets you look across many hills and notice whether they are tightly packed, scattered, or arranged in shapes that follow the rock. The geopark guide on this site, Gunung Sewu Geopark: karst hills of southern Java, describes the wider setting, and the district overview on the Gunungkidul travel guide places the hills within the local roads and villages.
Gunung Sewu as a UNESCO geopark
Gunung Sewu was announced as part of the UNESCO Global Geopark Network in September 2015. The designation recognises the landscape as a place of geological and cultural interest rather than as a set of individual viewpoints. For the hills, the designation means that the surface features, the caves and the underground water are considered together, because each depends on the others.
Visitors who want to understand the hills should treat the geopark as a whole. A single cone hill tells you about the rock in one place, but the wider pattern of hills, depressions and water routes tells you how the region works.
What the hills mean for people who live there
Life on cone karst is shaped by the lack of surface water. Villages cannot depend on rivers running through the valleys, and water has to be found, stored or drawn from underground. The underground rivers and springs that support communities are products of the same landform. The shape of the hills and the flow of the water explain why the region is hard to farm and easy to misread from the road.
Within a single district the land can change quickly from one depression to the next, so a map at district scale hides much of the variety that matters on the ground. Farmers, builders and road crews all have to read the shape of the land before deciding where to put anything.
For anyone thinking about building, road work or quarrying on cone karst, the main lesson is that the surface is uneven and can change. A hollow can drain into a conduit, and a cut slope can behave differently from one shaped in solid rock. The landform is not hostile, but it does require the builder to read the shape of the ground before deciding where to place anything.
Frequently asked questions about cone karst in Gunung Sewu
Is cone karst the same as tower karst?
No. Cone karst is made of many rounded hills with closed depressions between them, and it can sit across a wide range of terrain. Tower karst is made of steep, isolated towers that usually stand on plains or basins. The two can look quite different on the ground, and the distinction matters for understanding how each landform developed.
Why are the Gunung Sewu hills not all the same shape?
The shape depends on the rock, its fractures and how water has worked on it over time. Harder rock keeps its outline, while more porous rock is worn away faster, so neighbouring hills can differ even when they are made of the same limestone.
How many hills are in Gunung Sewu?
The number is not settled. The total is commonly given as roughly 40,000 cone hills, but the figure depends on how a hill is defined and how far the count covers. Treat any single number as an approximate guide.
Where can you see the hills best?
From a high point or ridge, where you can see many hills at once and notice how tightly they are packed. The geopark guide and the Gunungkidul travel guide on this site point to the viewpoints and roads that give that view.
Related guides: Gunung Sewu Geopark: Karst Hills of Southern Java, Swallow Holes in Gunung Sewu: Where Rivers Go Underground.