Sailing the Krakatoa seas

March 13, 2018

Scenic sunset in Kepulauan Seribu ("Thousand Islands") on the 6th day of the voyage (Photo: Shermaine Yung)

On 25 February, 15 NUS staff, students and alumni set off on a week-long NUS Study Trips for Engagement and EnRichment (STEER) voyage in collaboration with Tembusu College, from Jakarta to the Krakatoa archipelago. The trip was the ninth voyage by NUS Seafarers, an initiative of the Office of the Senior Deputy President and Provost, which has to date brought more than 100 NUS students and alumni on experiential sailing trips across Indonesia and the Philippines, teaching them about the biodiversity, as well as the economic, cultural and geographical aspects of these maritime nations. 

Associate Professor Martin Henz, NUS Computing and NUS Engineering, and Dr John van Wyhe, NUS Biological Sciences and Tembusu College Fellow pen their insights on the voyage.

How might one fathom the vastness of the biggest explosion in human history, the Krakatoa eruption of 1883? Can textbooks ever adequately convey the immensity of such events, the destruction they wreak and the regional and even global fallout they produce?

The Krakatoa catastrophe took place only 135 years ago, and many of the resulting geological features still stand in plain sight. Thus, our response to the educational challenge was to take the students on-site and immerse them in the landscape formed by that catastrophic event. 

We organised a Tembusu College STEER voyage — our “Recess Week Volcano Voyage” — to the Krakatoa archipelago for nine NUS students, two international exchange students and two NUS alumni. 

We boarded the 78-foot staysail schooner “Four Friends” in Jakarta on 24 February, set sail on the afternoon of 25 February, and reached the Krakatoa archipelago in the Sunda Strait in the early morning hours of the following day. 

seafarers-2.jpgIn front of Rakata Island, the largest remnant of the original Krakatoa volcano (Photo: Shermaine Yung)

The next three days provided ample opportunities to study the archipelago, consisting of Rakata, the tallest island which is often partially hidden by clouds and comprises the southern flank of the original pre-1883 Krakatoa volcano; two smaller Krakatoa remnants called Rakata Kechil and Sertung; and Anak Krakatau, a new volcanic island that emerged in 1927 from the vast seafloor hole created by the explosion. 

We explored the sea life that had re-established itself after the catastrophe, including several coral reefs and a large pod of dolphins, while snorkelling and navigating the area. We hiked through the tropical forests of Rakata and Rakata Kechil, which had grown back in the past 135 years on the fertile ash that the explosion had deposited on the surrounding islands. We established the heights of the peaks of Anak Krakatau (302m) and Rakata (810m) using sextant, GPS, radar and high school trigonometry. 


We examined rock samples from all four islands and conjectured their likely origin. While kayaking, we discovered pumice (volcanic rock) from recent eruptions, floating (yes, pumice is often lighter than water!) and washing up on the shores of the islands. We studied modern and historical maps and charts to complement our first-hand experiences.

Then, on 28 February, our third day in the archipelago, the stars aligned. A steady northerly monsoon wind exposed a cloud- and gas-free ascent path on the northern flank of Anak Krakatau. The seismic readings that we monitored using a satellite phone and with a Singapore-based collaborator showed benign levels of volcanic activity, and visual inspection of the crater elevated our hopes that a visit to the summit might be possible that day. We landed on the island using our motor boat and kayaks and made our way to the foot of the mountain through a vast and rugged lava field.

“Dr John” — as he was endearingly called by the students — scouted out a suitable route for our ascent, while the remaining team further inspected the lava field. Year 2 NUS Computer Science and University Scholars Programme (USP) student Chu Qinghao, Year 4 NUS Industrial Systems Engineering and Management student Daren Lau and Assoc Prof Henz decided to follow in the footholds that Dr John had prepared for them. Continuous Very High Frequency communication with the nearby anchored schooner and with each other during the ascent enabled us to react to any possible changes in the cloud pattern over the volcano and other signs of danger. 

seafarers-3.jpgClimbing a field of solidified lava leading to the crater of Anak Krakatau (Photo: Martin Henz)

The summit provided breathtaking views of the seascape towards Sumatra. Breathtaking in quite a different sense was the direction towards the caldera! We saw a complex amalgamation of igneous rock and ash riddled with a myriad of tiny holes from which hot water vapour and volcanic gases oozed. We flew a drone over the caldera and took movies and pictures, before carefully descending along the same path.

“The best part of the trip for me was being able to see Krakatoa itself up close after having read and heard so much about it. The scale of the place was astounding and I still find it hard to believe that I was at the site of such a significant event,” said Year 4 NUS Geography student Grace Tang.

Another participant, Year 2 NUS Business and USP student Wong Li Ching called it a multisensory learning experience in nature's classroom. “Spontaneous activities undertaken during the voyage encouraged experimentation and calculated risk-taking — these can hardly be learnt in the safe and organised learning environment in university. I felt connected to nature again,” she said.

Nicholas Seow, Year 4 NUS Geography student, added that the voyage proved that “geography is everywhere, you just need to be inquisitive and daring”.

Indeed, what better place to grasp the scale of the 1883 Krakatoa explosion than on top of the crater of Anak Krakatau, which grew from the depths of the sea at the site of the original volcano, with vapour and gases emerging from the ground on which we stood?


The Tembusu (Fagraea fragrans) is a large evergreen tree in the family Gentianaceae. It is native to Southeast Asia. Its trunk is dark brown, with deeply fissured bark, looking somewhat like a bittergourd. It grows in an irregular shape from 10 to 25m high. Its leaves are light green and oval in shape. Its yellowish flowers have a distinct fragrance and the fruits of the tree are bitter tasting red berries, which are eaten by birds and fruit bats.