After thirty years of researching the Toba caldera, Toba in North Sumatra feels like home to Craig Alan Chesner. “I have dedicated myself to studying the caldera. I’ve done my research on Toba for Indonesia,” said the American scientist.
“I have already fallen in love with Toba.”
He made the statement during a meeting of worldwide caldera experts at the 2018 International Workshop on Collapse Caldera (IWCC) in Toba Cottages, Tuk-Tuk, Samosir Island, North Sumatra, at the end of September. He was present as a senior researcher with the department of geology and geography, Eastern Illinois University. Among the caldera experts, he was dubbed the father of the experts of Toba’s caldera. That refers to his deep expertise on the caldera.
Cheshire’s research partly revolves around the bathymetric or depth and mapping of water bases, such as lakes or seas. Based on the research, Chesner said, the depth of Lake Toba was uneven, but varied, between 50 and 500 meters.
Chesner’s research has become a reference for the recovery of KM Sinar Bangun, which sank in July 2018 in Lake Toba. It is known that the ship was at the bottom of Lake Toba with a depth of 500 meters. This later became the basis of the evacuation policy.
As a researcher, Chesner was relieved that he was able to record the depth of Lake Toba in 2005 and 2008. He was even more relieved because the research could be utilized. “Even though I was relieved, I was still sad because it was related to an accident. Even if it can be lifted, the equipment must be strong and the cost is certainly very high,” he said with concern.
Bathymetric research conducted by Chesner used the method of extracting depth data with single-beam sonar. This method uses a sound propagation (frequency) detection process under the tugboat. Furthermore, recording sound propagation results in accurate maps of water depth.
The expert of the caldera, who was accompanied by several experts during the study, found around 60 dots that served as 30 connecting lines of Samosir Island and Sumatra Island that surround Lake Toba. If his travel is carried out in a stretched line, Chesner for more than two weeks has traveled 600 kilometers in a zigzag route. The results of the study were published in the scientific journal Quaternary International, Elsevier Ltd and INQUA entitled “The Toba Caldera Complex” (2011).
Chesner is a world class caldera expert who for 30 years has researched the Toba caldera. During that time, he has visited Toba 10 times and lived around a month on Samosir Island. Over time, he has become increasingly recognized by the people around Samosir. He admitted that he really enjoyed it.
“If I come to Samosir, I always feel like going home. The hospitality of the people is not forgotten, especially its natural beauty, extraordinary,” he said with a smile.
He recalled when he first arrived in Toba, the residents of Samosir thought he was Hollywood film star Chuck Norris. He indeed looked similar, especially because he kept a beard like Norris. The children followed him and called him, “Mister […] mister!”
When Chesner took samples of the rock walls or dug up soil to examine the layers in several locations, the children and some residents were amazed. “What is mister doing? How come, mister is digging and taking notes … Digging again, then taking notes again. Mister also collects some rocks. What exactly is mister doing?” Chesner said, mimicking the questions from the residents.
“Well, they asked those questions in the first year I came to research. I am happy with their questions. That is, they care about the surrounding environment,” Chesner said.
The 60-year-old caldera expert is friendly and not stingy to anyone who greets and asks him. As long as it alludes to his research on the Toba Caldera, he enthusiastically and kindly answered it.
Challenges from lecturers
Chesner came to Toba for the first time in 1987 because one of his supervisors gave him a challenge to research the Toba Caldera. After he arrived once, he was hooked to continue and continue to research there.
He advised the young researchers to learn from the Toba Caldera. Toba, according to him, is a complete natural laboratory and has a large eruption trail that is intact to continue to explore. A massive eruption that left a crater more than 2,000 meters (2 kilometers) in diameter. That is the caldera.
“Toba erupted three times and the latest was recorded 74,000 years ago. If you go around Samosir Island, you will see towering walls that are parts of the eruption — during and after the eruption,” he said.
Toba Caldera is the largest caldera in the world approximately measuring 100 kilometers x 30 kilometers. The caldera character is rare, which comes from the eruption of the lake base that was lifted because of the very powerful magma kitchen underneath. Samosir Island is still active, going up to one millimeter per year.
There are many memories for Chesner, who has to travel for about 42 hours from his home in the United States with air transportation to Samosir Island. His left hand once was broken after falling down from a motorbike in Samosir. He must carry two bags containing sample rocks to study. He must take care of various permits to transport the rocks from the airport to the airport to get to his laboratory in America.
“This Toba caldera is so rich in science. It was the right decision to research directly here. There are still many things that have not been explored and examined because of the vastness of this caldera. I hope young researchers are interested in coming and studying here from all over the world,” he said with full enthusiasm.
Born: June 1958
Education: BA in Geology in 1980 from Franklin and Marshall College; Master and doctor in geology from Michigan University of Technology
Career: Professor in geology at the Department of Geology/Geography, Eastern Illinois University (1989 – present).