Returning to Krakatau: Diving for Rock Samples and Building Research Bonds
One year after the R/V SONNE cruise, GEOMAR researchers returned to the waters around Anak Krakatau to gain a deeper understanding of an intriguing discovery made during their previous expedition. This latest endeavour, part of an on-going collaboration with BRIN, Indonesia’s national research and innovation agency, aimed not only to collect geological samples but also to strengthen scientific ties between GEOMAR and Indonesian researchers.
To unravel the mechanisms behind the catastrophic volcanic events of 1883 and 2018 at the Krakatau volcanic complex, GEOMAR’s PRE-COLLAPSE team conducted surveys using bathymetry, sediment echosounders, 2D seismic profiles, and sediment gravity coring during a research cruise onboard R/V SONNE in August 2023. As part of precise mapping, these efforts led to the discovery of extensive underwater rock fields southwest of Sertung Island, which have not yet been described or interpreted by the research community. As often happens in research, new discoveries cannot only enhance understanding but also challenge previous hypotheses and raise new research questions.
Could these rock fields shed light on the mechanisms behind the 1883 Krakatau explosion and the resultant tsunami? Understanding the nature of these rock fields and the sequence of their formation and deposition could reveal additional processes involved in tsunami generation. To answer these questions, the researchers needed rock samples from the seafloor, but how do they collect them, when large ships can't access the area? By diving.
Diving Expeditions to Collect Rock Samples
GEOMAR researchers typically use ROVs (Remotely Operated Vehicles) to collect samples from the seabed when sediment corers or dredges are not feasible. However, for this mission, the best approach was for real people to dive and manually collect the samples. Professor Morelia Urlaub and Postdoctoral Researcher Séverine Furst visited Krakatau Volcanic Complex and Java in August 2024. The highlight was a two-day expedition to Anak Krakatau Island. They were joined by three Indonesian researchers from BRIN, Semeidi Husrin, Daulat August, and Shofia Karima, and five professional divers, including two local experts with extensive knowledge of the area.
Equipped with cameras and briefed by the scientific team on how to locate large, house-sized blocks on the seabed, the divers explored the ocean floor southwest of Sertung Island. At depths of up to 40 metres, they encountered contrasting underwater landscapes, from sandy ocean floors with strong currents to coral-covered, blocky submarine realms. Despite the challenges of open-water diving, which is significantly more difficult than reef diving, across six dives they successfully collected several volcanic rock samples. The exact nature of these rocks will be determined through dating and petrological and petrographic analyses at BRIN and GEOMAR, promising valuable insights into the volcanic history and activity of the region. By comparing the major and trace element compositions of these offshore samples with well-documented onshore samples from the islands, the researchers aim to answer key questions about the rocks' origin, age, and the processes that transported them to their current locations.
Scientific Collaboration
Following the diving expedition, Morelia Urlaub and Séverine Furst spent a week at BRIN's facilities in Bandung, Java, where they had the opportunity to meet researchers and representatives of various research centres. During a dedicated workshop on Krakatau, they exchanged ideas and knowledge, discussing future procedures and projects.
The collaboration allowed the GEOMAR team to learn from Indonesia's rich local expertise and deep understanding of their volcanoes. “This trip to Indonesia was not just about understanding Krakatau's geological past—it's about building stronger international collaborations and advancing our collective knowledge of volcanic processes and tsunami generation,” emphasised Morelia Urlaub. She was impressed by the diverse expertise and deep knowledge the Indonesian researchers hold about their home volcanoes, adding, “It’s the things between the lines, like hearing about eyewitness reports that make such meetings especially valuable.”
The partnership also provided the GEOMAR team with insights into Indonesia's tsunami warning system, which includes strategically placed sea level gauges around Krakatau and along the coast of West Java. Integrated into the international tsunami warning network, these gauges provide real-time data on sea levels and wave patterns, offering crucial early warnings for potential tsunamis in the Krakatau region.
Visiting Research Fellowship at BRIN
Séverine Furst extended her stay at BRIN for four weeks under a visiting research fellowship, during which she worked on the sample preparation and description, engaged in further scientific exchange, and had the opportunity to visit the Merapi Volcano Observatory. “The hands-on experience from field trips, workshops, and interactions with specialists has not only refined my research skills but also contributed to developing a robust scientific network,” she said about her time in Indonesia.
This collaboration has been mutually beneficial, enhancing the research capabilities of both GEOMAR and BRIN. German researchers have gained invaluable insights from Indonesia’s local expertise, while BRIN has strengthened its research foundation for future projects. The exchange fostered a collaborative spirit that promises a deeper understanding of volcanic and tsunami hazards, not only in the Krakatau region.
BRIN, Indonesia’s National Research and Innovation Agency
Diving vessel and divers in the waters southwest of Sertung Island. (Images: Séverine Furst)
The diving team led by Samsul Hidayat (Balawista Carita Beach) discussing their expedition to collect rock samples at the seafloor southwest of Sertung Island. (Image: Séverine Furst)
Anak Krakatau and its surrounding islands in the Sunda Strait between Java and Sumatra during the eruption on February 3rd 2022. (Image: Copernicus)
(credit: Earth System Knowledge Platform, eskp.de)
Participants of the Krakatau workshop at BRIN, excluding those who attended via Zoom. They exchanged ideas and knowledge, discussing future procedures and projects. Séverine and Morelia presented the outcomes of last year's SONNE expedition to Krakatau. (Image: Franto Novico)
Delegation of BRIN's Geological Disaster Research Centre met with Morelia and Séverine. From left: Wilfridus (Willy) Banggur (volcanologist, researcher), Adrin Tohari (Reserach Director of the Geological Disasters Group), Shofia Karima, Morelia Urlaub, Semeidi Husrin, Séverine Furst, Franto Novico. (Image: Franto Novico)
Participants of the diving expedition at a pre-meeting. (Image: Semeidi Husrin)
The international research group enjoys traditional Sundanese cuisine. (Image: Séverine Furst)
Indonesian and german researchers decribe the rock samples (Image: Semeidi Husrinv)
On land, at Anak Krakatau, the team was able to observe stratigraphic formations, including pyroclastic and ash deposits in erosion gullies right next to their camp area. Also they were finally able to visit the crater itself with the fumaroles, sulfur and steam coming out. Check out the drone video below. (Images: Séverine Furst)
Drone Video flying over the Anak Krakatau Crater (Saud @sudive.sudrone)
Indonesia Tsunami Early Warnining System
Semeidi Husrin is involved in the development and implementation of the tsunami early warning system in Indonesia, specifically focusing on the Inexpensive Device for Sea Level Monitoring (IDSL). This system, developed in collaboration with the European Commission's Joint Research Centre, aims to enhance tsunami detection and warning capabilities by installing low-cost, easily deployable sea level monitoring devices in key locations across Indonesia. These devices are integrated into the broader national monitoring network and contribute significantly to tsunami mitigation efforts in the region.
Semeidi Husrin and Morelia Urlaub on board of the diving vessel during the Krakatau expedition (image: Morelia Urlaub).
