Krakatoa (or Krakatau) is an archipelago in the Sunda Strait of Indonesia, located between the islands of Java and Sumatra. This volcanic complex is globally recognized for the catastrophic eruptions that occurred in August 1883. The power of these events established the volcano’s reputation as one of the most destructive natural forces ever recorded. The history of Krakatoa is a study of geological violence followed by remarkable biological recovery.
The 1883 Eruption: Mechanics of Destruction
The cataclysmic phase of the 1883 eruption began on August 26, following months of smaller activity. A series of four massive explosions occurred on August 27, culminating in the final, most intense blast at 10:02 a.m. local time. This event involved the volcano collapsing inward, which obliterated nearly two-thirds of the main island mass and created a massive submarine caldera. The explosion registered a 6 on the Volcanic Explosivity Index (VEI).
The island’s destruction was followed by pyroclastic flows and immense tsunamis. Pyroclastic flows, which are superheated clouds of ash, gas, and rock fragments, traveled at high speed across the sea surface. One flow traversed the 40-kilometer-wide Sunda Strait, reaching Sumatra and killing approximately 1,000 people. The collapse of the volcanic edifice into the sea displaced an enormous volume of water, generating devastating waves.
The largest waves reached up to 42 to 46 meters along the coastlines of Java and Sumatra. These waves swept away over 165 coastal villages and settlements, accounting for the vast majority of the estimated 36,417 deaths. The force of the tsunamis was sufficient to fling massive chunks of coral reef, weighing hundreds of tons, far onto the shore.
The final explosion at 10:02 a.m. remains the loudest sound ever documented in modern history. The acoustic pressure wave ruptured the eardrums of sailors 40 miles away. The sound was heard across more than 10% of the Earth’s surface, reaching Rodrigues Island near Mauritius, some 4,800 kilometers away. The energy released by the volcano reshaped the local geography, leaving behind only small remnants of the original island.
Worldwide Atmospheric and Oceanic Impact
The eruption’s effects extended far beyond the immediate region, influencing the entire globe through atmospheric and oceanic phenomena. The acoustic pressure wave traveled multiple times around the planet, registering on barographs (pressure-measuring instruments) worldwide for days.
The volcano injected gas and pulverized material, including sulfur dioxide and fine ash, high into the stratosphere, reaching altitudes of up to 20 kilometers. These stratospheric aerosols circled the Earth, creating a global veil that acted as a solar radiation filter. Consequently, global average air temperatures dropped by approximately 0.5°C to 1.2°C in the year following the eruption, a temporary cooling effect known as a volcanic winter.
The fine particles scattered sunlight, producing spectacular, prolonged sunsets and optical effects for several years. Vivid red and purple twilight skies were reported globally, and the phenomenon was immortalized in art, such as in the works of Edvard Munch. The displacement of water also generated transoceanic tsunamis recorded on tide gauges thousands of miles away, including in the English Channel and off the coasts of South Africa.
The Return of Life: Ecological Succession
The 1883 eruption sterilized the remaining islands, burying them under meters of ash and pumice, creating a blank canvas for life. This provided a unique laboratory for studying primary ecological succession—the process by which life returns to a barren environment. Scientists documented the gradual recolonization of the islands, which began almost immediately.
The first signs of life were pioneering species whose spores or seeds were carried by wind and sea currents. Within a year, a single spider was discovered, and simple organisms like blue-green algae began to form a crust on the volcanic ash. Ferns and mosses, easily dispersed by wind, soon followed, establishing themselves in the hostile environment.
Within a few decades, the landscape transitioned through distinct ecological stages. The initial pioneers gave way to dense fields of grass, particularly species like Saccharum spontaneum, creating a savanna across the island remnants. This grass cover helped stabilize the ash and contributed organic matter to the nascent soil.
As the soil improved, the islands saw the arrival of species dispersed by the sea, such as coastal shrubs, followed by plants carried by birds and bats. By the mid-20th century, the islands were blanketed in a mature tropical forest, demonstrating resilience and speed of recovery. The study of Krakatoa continues to provide insights into island biogeography and the ability of ecosystems to rebuild after catastrophic disturbance.
Anak Krakatoa: The Next Generation Volcano
The submerged caldera created by the 1883 collapse did not remain dormant for long, as volcanic forces continued beneath the surface. In 1927, new eruptions began within the submerged crater, leading to the formation of a new volcanic cone named Anak Krakatoa, meaning “Child of Krakatoa.” This new volcano rapidly emerged from the sea and continued to grow, frequently erupting and adding new layers of lava and ash.
By 2018, Anak Krakatoa had grown to approximately 300 meters above sea level, a steep and unstable structure of loose volcanic material. On December 22, 2018, an eruption triggered a major flank collapse on the volcano’s southwestern side. This event saw an estimated 0.2 to 0.4 cubic kilometers of the cone slide rapidly into the Sunda Strait.
The sudden landslide generated a devastating local tsunami that struck the coastlines of Java and Sumatra with virtually no warning. The resulting waves caused the deaths of hundreds of people and underscored the ongoing geological hazard presented by the still-active volcanic complex. Anak Krakatoa continues to undergo periods of growth and collapse, serving as a reminder of the ongoing cycle of devastation and rebirth in this volatile region.