Layered marine sediments uplifted to 500m elevation. Each layer records ancient climate cycles, creating a continuous record of monsoon intensity for 5 million years.
An ocean floor on a mountainside
Along the Wae Lare river on the island of Flores, a unique geological formation rises to 500 meters above sea level. This is the Flores pelite formation, a thick sequence of fine-grained sedimentary rock that was once mud on the deep ocean floor. Its existence on a mountainside results from immense tectonic forces. Flores is located at a complex junction between the Eurasian and Indo-Australian plates. The collision of the Australian continental crust with the island arc has been forcing the island upwards for millions of years.
The uplift in central Flores has been measured at approximately 800 meters over the last 2.5 million years, a rate of about 0.32 millimeters per year. This slow, persistent process lifted ancient marine deposits high into the air, exposing them to the elements. The formation is primarily composed of pelite, a sedimentary rock formed from consolidated clay and silt. Within these layers, scientists have found an almost unbroken record of the region's climate history, stretching back into the Pliocene epoch.
Reading the climate record
Each thin layer in the pelite formation acts as a page in a climatic diary. The sediments preserve chemical signatures, known as proxies, that reflect environmental conditions at the time of their deposition. Scientists analyze these proxies to reconstruct the intensity of the Australian-Indonesian monsoon system over geological time.
One important proxy is the element thorium, specifically the isotope 232Th, which is delivered to the ocean exclusively from the weathering of continental rocks. Higher concentrations of thorium in a layer indicate periods of intense rainfall and increased river runoff from the surrounding landmasses. By measuring the changing concentrations of these elements up through the sediment core, researchers can map out the fluctuations in monsoon strength. This data provides a high-resolution look at past climate, showing how the monsoon system responded to global climate shifts, such as the ice ages of the Pleistocene. The record provides a long-term record on the dynamics of the Intertropical Convergence Zone, the band of tropical rainfall that governs the climate for a massive portion of the world's population.
💡Fun Facts
The island of Flores is tectonically active, situated where an oceanic-island arc subduction zone transitions into a continental-island arc collision zone.
The uplift rate of about 0.32 mm per year means the formation has risen by the height of a 16-story building every 200,000 years.
The climate data from these sediments provides environmental context for the era when the ancient hominin *Homo floresiensis*, nicknamed the "Hobbit," lived on the island.
Proxies used to study past climates can include sediment chemistry and trapped pollen grains, microfossils, and even gases captured in ancient ice.
Accessible at all times, as it is a natural, unfenced geological feature.
Admission
Free.
Accessibility
The formation is in a remote, natural area. Access requires overland travel from a town like Bajawa or Ende, likely followed by a trek. The terrain is rugged and not suitable for wheelchairs or visitors with mobility issues. Hiring a local guide is recommended.
The Flores pelite formationEast Nusa Tenggara, Indonesia