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Mount Bromo and other volcanoes above a sea of mist at sunrise, on the island of Java

Natural wonder Asia

Java

Java is an island in Indonesia with many volcanoes. Some of them puff out steam and ash. Rare Javan rhinos live in a forest at one end of the island.

Java is an island of Indonesia on the Pacific Ring of Fire, and it has many active volcanoes. Its tallest, Mount Semeru, is also its most active. At its western tip, Ujung Kulon National Park protects the island's largest remaining lowland rainforest and the endangered Javan rhinoceros.

Java, in Indonesia, lies on the Ring of Fire and has many active volcanoes, NASA's Earth Observatory notes; Semeru, rising 3,676 m above the nearby coastal plains, is its tallest and most active. In the east, Bromo is a cinder cone inside the Sandsea Caldera, part of the larger Tengger Caldera, which formed about 8,000 years ago. In the far west, UNESCO's Ujung Kulon National Park shelters the Javan rhinoceros.

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Photo: Thomas Hirsch (= user Ravn), CC BY-SA 3.0, via Wikimedia Commons

Discover Java

Java is an island in Indonesia. It has many volcanoes.

This photo was taken at sunrise. Morning fog fills the land around the volcanoes, and two of them are puffing out smoke.

Java is an island of Indonesia. It is part of the Ring of Fire, a zone of frequent earthquakes and volcanic eruptions that partly rings the Pacific Ocean, and it has many active volcanoes. Mount Semeru, the tallest volcano on Java and also its most active, rises 3,676 meters above the nearby coastal plains, NASA says.

This photo, taken at sunrise in September 2002, shows the Tengger volcanoes in eastern Java, with morning fog all around them.

NASA's Earth Observatory places Java on the 'Ring of Fire', a zone of frequent earthquakes and eruptions that partially rings the Pacific basin, and describes the island as having many active volcanoes. It calls Semeru, rising 3,676 m above the nearby coastal plains, Java's highest volcano and, in 2022, its tallest and most active one; Merapi and Semeru both rank among Indonesia's most active volcanoes.

The hero photo, a Wikimedia Commons featured picture by Thomas Hirsch, shows the Tengger massif at sunrise on 26 September 2002: Bromo's smoking crater, Batok in front and Semeru smoking in the distance.

Country
Indonesia
Tallest volcano
Mount Semeru, rising 3,676 m
Tengger's Sandsea Caldera formed
about 8,000 years ago
World Heritage Site
Ujung Kulon National Park (1991)
Mount Bromo and other volcanoes above a sea of mist at sunrise, on the island of Java
Photo: Thomas Hirsch (= user Ravn), CC BY-SA 3.0, via Wikimedia Commons

Volcanoes inside a volcano

Long ago, a huge eruption left a giant bowl in the ground called a caldera.

Later, new little volcanoes grew inside the bowl. Bromo is one of them.

Mount Bromo is a small but active volcano in the middle of a giant bowl called the Sandsea Caldera. That caldera is part of an even bigger one, the Tengger Caldera. The Sandsea Caldera formed about 8,000 years ago in what must have been a massive eruption.

Later eruptions built a cluster of small cones on the caldera floor, including Bromo. Records show Bromo has erupted every few years since 1804.

NASA's Earth Observatory describes Gunung Bromo as a small but active cinder cone in the center of the Sandsea Caldera, itself only a portion of the larger Tengger Caldera; a caldera is the circular depression in a volcano's summit area. The Sandsea Caldera formed around 8,000 years ago, in what must have been a massive eruption.

Subsequent activity built the cluster of cinder cones on the caldera floor. The historical record shows eruptions of Bromo every few years since 1804, and geologic evidence points to eruptions at least several hundred years earlier.

Rainforest and rhinos

At the far west end of Java there is a big rainforest park.

Javan rhinos live there. They are very rare, so the park keeps them safe.

At the far southwestern tip of Java lies Ujung Kulon National Park, a World Heritage Site since 1991. It has the largest remaining area of lowland rainforest on the plains of Java, UNESCO says.

Several kinds of endangered plants and animals live there. The one in the most danger is the Javan rhinoceros. The park also takes in several offshore islands and the Krakatoa nature reserve.

UNESCO's Ujung Kulon National Park (inscribed 1991, criteria (vii) and (x)) lies at the extreme south-western tip of Java on the Sunda shelf. It includes the Ujung Kulon peninsula, several offshore islands and the natural reserve of Krakatoa, and is of geological interest, particularly for the study of inland volcanoes.

It contains the largest remaining area of lowland rainforest in the Java plain, and several endangered plant and animal species, of which the Javan rhinoceros is the most seriously under threat.

Visiting safely

Volcanoes can be dangerous. Grown-ups check the warnings before a visit.

When scientists say to stay away from a volcano, everyone keeps back.

Indonesia's volcano agency, the Center for Volcanology and Geological Hazard Mitigation (PVMBG), uses an alert scale from 1 to 4 and tells people how far to stay away from an erupting volcano. Its current warnings are worth checking before any visit.

When Semeru erupted strongly in December 2022, the agency raised it to level 4, the highest, and asked people to stay at least 5 kilometers from the summit and away from a river valley on its slope.

PVMBG, Indonesia's Center for Volcanology and Geological Hazard Mitigation, uses a 1-4 alert scale. NASA's Earth Observatory reports that during Semeru's eruption of 3-4 December 2022, which sent ash as high as 6,100 m and pyroclastic flows down the southeastern flank, PVMBG raised the status to level 4 ('awas') and urged people to stay at least 5 km from the summit and 500 m from the Besuk Kobokan river channel.

The general lesson for visitors: follow the agency's current alert level and exclusion zones, which change with each volcano's activity.

Amazing facts

  • Mount Bromo is a little volcano inside a giant old one!

    Bromo sits inside the Sandsea Caldera, which is part of the even bigger Tengger Caldera.

    Bromo is a cinder cone in the center of the Sandsea Caldera, itself only a portion of the larger Tengger Caldera (NASA Earth Observatory).

  • In 2022, ash from Semeru rose more than 6 kilometers into the sky!

    In December 2022, ash from Semeru rose as high as 6,100 meters at times.

    During the 3-4 December 2022 eruption, Semeru's gas and ash rose as high as 6,100 m at times, according to the Darwin Volcanic Ash Advisory Center (NASA Earth Observatory).

  • The Javan rhino is the animal in the most danger in Java's big rainforest park.

    Of all the endangered plants and animals in Ujung Kulon National Park, UNESCO says the Javan rhinoceros is the most seriously under threat.

    UNESCO lists several endangered species in Ujung Kulon, the Javan rhinoceros being the most seriously under threat.

  • Bromo has been erupting again and again for more than 200 years.

    Records show Bromo erupting every few years since 1804, and rocks show it erupted even several hundred years before that.

    The historical record shows Bromo eruptions every few years since 1804; geologic evidence indicates eruptions at least several hundred years earlier.

Words to know

volcano
an opening in the ground where melted rock, ash and gas come out
caldera
a large round hollow left at the top of a volcano after a big eruption
cinder cone
a small, steep volcano built from bits of rock thrown out in eruptions
Ring of Fire
a zone of frequent earthquakes and volcanic eruptions that partly rings the Pacific Ocean
plume
a tall cloud of gas, steam or ash rising from a volcano
lowland rainforest
a thick, wet forest growing on low, flat land

Discovery challenge

  1. Which is the tallest volcano on Java?

    Which volcano is the tallest and most active on Java?

    Which Javan volcano, rising 3,676 m above the coastal plains, does NASA call the island's tallest and most active?

    • Mount Semeru
    • Mount Bromo
    • Mount Batok
    Show the answer

    Mount Semeru

    Mount Semeru.

    Mount Semeru, which rises 3,676 meters above the nearby coastal plains.

    Semeru.

  2. What is the giant bowl around Bromo called?

    What is the big hollow that Bromo sits in called?

    Which caldera, formed about 8,000 years ago, contains Bromo?

    • A caldera (the Sandsea Caldera)
    • A lagoon
    • A glacier
    Show the answer

    A caldera (the Sandsea Caldera)

    A caldera.

    The Sandsea Caldera, part of the larger Tengger Caldera.

    The Sandsea Caldera, a portion of the Tengger Caldera.

  3. Which rare animal lives in Java's big rainforest park?

    Which endangered animal does UNESCO say is most under threat in Ujung Kulon?

    Which species does UNESCO single out as most seriously under threat in Ujung Kulon National Park?

    • The Javan rhinoceros
    • The polar bear
    • The kangaroo
    Show the answer

    The Javan rhinoceros

    The Javan rhino.

    The Javan rhinoceros.

    The Javan rhinoceros.

  4. Since when have people written down Bromo's eruptions?

    Since which year does the record show Bromo erupting every few years?

    From what year does the historical record of Bromo's frequent eruptions begin?

    • 1804
    • 1954
    • 2004
    Show the answer

    1804

    Since 1804, more than 200 years ago.

    Since 1804.

    1804; geologic evidence goes back several hundred years further.

  5. Before visiting a volcano, what should grown-ups check?

    What should visitors check before going near a volcano in Indonesia?

    Which official information should guide a visit near an active Indonesian volcano?

    • The volcano agency's alert level and safe distances
    • Only the weather for sunbathing
    • Nothing at all
    Show the answer

    The volcano agency's alert level and safe distances

    The volcano warnings.

    PVMBG's alert level (1 to 4) and the distances to keep.

    PVMBG's current alert level and exclusion zones.

Nearby places

Explore next

For parents & teachers

What children will learn

  • Locate Java and explain what the Ring of Fire is.
  • Explain what a caldera and a cinder cone are.
  • Describe why Ujung Kulon National Park matters.
  • Know that volcano alert levels and exclusion zones keep people safe.

Recommended ages: 3 to 17 · About 15 minutes

Talk about it

  • How can a small volcano grow inside a much bigger, older one?
  • Why might scientists change a volcano's alert level from day to day?
  • Why might one protected forest matter so much for a rare animal?

Try at home or in class

  • With a grown-up, fill a bowl with sand, press a large hollow into the middle, then build a small cone inside it: a model of Bromo inside its caldera.
  • Find Java on a map of Indonesia, then find the Pacific Ocean and trace the Ring of Fire around it.

Key vocabulary: volcano, caldera, cinder cone, Ring of Fire, plume, lowland rainforest

Where these facts come from

  1. Wikidata , Wikimedia Foundation (CC0 1.0)
  2. Gunung Bromo, Indonesia (Image of the Day, 7 December 2004) , NASA Earth Observatory
  3. Java and the Merapi Volcano (Image of the Day, 16 May 2006) , NASA Earth Observatory
  4. A Burst of Activity at Mount Semeru (Image of the Day, 6 December 2022) , NASA Earth Observatory
  5. Ujung Kulon National Park , UNESCO World Heritage Centre
  6. Natural Earth vector data , Natural Earth (NACIS) (Public domain)
  7. Wikimedia Commons , Wikimedia Foundation (Per file (public domain, CC0, CC BY or CC BY-SA); see each media record)

Checked, not yet human-reviewed. Last updated November 1, 2026. Spotted a mistake? Tell us.

Picture credits
  • Photo: Thomas Hirsch (= user Ravn), CC BY-SA 3.0, via Wikimedia Commons · source · license