As Earth Tells Si Si Tao Toba and Bukit Barisan

Bandung, fitb.itb.ac.id This article appeared in the book potpourri Geographic Expedition 2009 North Sumatra Indonesia (Bakosurtanal – Coordinating Agency for Surveys and Mapping Agency).
book cover

“Basic fish you boy!”

Suddenly the earth shook violently. The massive earthquake that shook the mountainous land. Longitudinal fissure cracked ground. Soon the water gushed out unceasingly through the cracks-cracks of soil and rocks. On top, dark clouds hung heavy in the black sky. Lightning strikes the earth with a thrilling voice. Rain was pouring down continuously. The new Toba realized, to his expletives Naidoo has been opened should closely guarded secrets about the origins of his wife, who had a pretty big fish that once he gets.

Remorse came later. Water soon flooded the valley where the Toba is located and drown. That reward for taking care of their children impatience Naidoo who is naughty and voracious eating. Naidoo, on the orders of his mother, who again changed into fish, survived the climb up the hill. Valleys were flooded area was later turned into a lake, Tao Toba. Bukit Samosir place to escape into the island.

Thus the legend of Lake Toba is known in children’s stories archipelago. Moral of the story reminds us to always patient care of children and maintain the honor of the household. But behind it is implied extraordinary natural events on the formation of Lake Toba. Geologically already known how the largest lake in Indonesia is formed through the events paroksismalis between activity and tectonic plate movement, volcanic eruptions.

supervolcano Toba

Far from Toba, in a layer of ice freezing in Greenland near the North Pole, in the early 1970s experts glacial geology and paleoclimatology surprised to find ice core drilling sludge containing sulfuric definite anomaly associated with the deposition of volcanic ash. Thousands of volcanoes scattered over the Earth, volcanic deposition Which ashes scattered to the North Pole? The study found the data were astounding. Clive Oppenheimer in 2002 declared the anomaly associated with volcanic ash deposited by a volcanic eruption events 74,000 years ago. Precipitates with thicker same age found during the drilling of the seabed in the Indian Ocean and the Arabian Sea during the late 1980s and early 1990s. Everything turned out equivalent to the old white precipitate widespread in the highlands around Lake Toba. That is what is known as tuff Toba (Toba tuffs).

In the prehistoric era, 74,000 years ago, predicted a series of devastating volcanic eruptions have occurred along the cracks at the boundaries of the northeast and southwest of Lake Toba. R.W. van Bemmelen, a Dutch geologist – whose book “The Geology of Indonesia, 1949” always been a reference geology of Indonesia – in 1929 and 1939 put forward a hypothesis formation of Lake Toba. According to him, a pembumbungan the central part of North Sumatra, known as “tumor Batak” became the forerunner to the formation of Lake Toba. The tumor was incredible erupted violently combination of processes of volcanic and tectonic, causing the central part of the tumor amblesnya form a basin extends northwest – southeast, serarah elongated island of Sumatra, and also the direction of the Great Sumatran Fault and Bukitbarisan Mountains. That process also causes “terungkitnya” portion of subsidence, lifted his side to the southwest, forming the island.

Bemmelen opinion that has survived so long since 1929 was finally disproved by geomorphological research done by Verstappen during 1961 – 1973. He found their structural terraces in the steep canyons Sei Asahan in Siguragura on which deposited Toba tuff. It shows that Sei Asahan have formed long before the massive eruption of Toba according Bemmelen in 1929. That is, there is a possibility basin existed before the Toba eruption, or what was introduced by Bemmelen as the eruption of volcano-tectonic. Eruptions of it occurs in volcanoes are likely to occur in cracks and fault-fault that flank the steep escarpment escarpment-valley Lake Toba.

Eruptions large gray paroxysmal spitting up all the layers of the stratosphere and spread around the surface of the Earth. Thick precipitate certainly falls around the eruption center around Lake Toba, resulting in Toba tuff, white rock with grains of volcanic glass, fragments of quartz and clay-sized glass matrix. The incident did not take place in one time only. The results of the study of stratigraphic layers Toba tuff and measuring absolute age, showed layers of tuff eruption of about 74,000, 450,000, 840,000, and 1.2 million years ago, resulting in a looping 375,000 years with a standard deviation of 15,000 years (Chesner et al. 1991 and Dehn et al., 1991, in Rampino & Self, 1993).

Rampino and Self (1993) suspect that the Toba eruption has produced volcanic ash eruption 2,800 km3 as high as 40 km into the sky which then can lead to cooling of the Earth‘s surface suddenly. Rampino and other researchers call the phenomenon of global cooling as a “volcanic winter”. Earth’s temperature fell an average of 3 – 5 ° C. It is probable eruption 74,000 years ago affects the inhabitants of Earth and humans at that time. Globally known of the symptoms associated with the bottle neck populations declined drastically human population coincide in time 74,000 years ago. In the archipelago, with the evidence of fossils found in Java, Homo erectus, and humans are more modern types such as Human Wajak, most likely to feel the impact of the massive eruption of Toba great. Indeed, there is no strong evidence of the phenomenon of Toba caused the extinction of the human species, but the influence of climate change is certain to change the pattern of their lives.

The closest example of global climate change due to volcanic eruptions is after the eruption of Krakatoa in 1883, and especially the eruption of Tambora in April 1815 were 10 times more powerful than the 1883 Krakatoa eruption has caused a strange phenomenon that snow in July in Europe, so in 1815 dubbed “the year without summer.” The years after it caused crop failures around the world due to global climate chaos.

Beginning in 2005, a view that has finally recognized misquoted by researchers from Monash University in Australia, Raymond Cas, stating their giant mass of magma beneath Lake Toba supervolcano to erupt as. The opinion makes this panic immediately contradicted many experts. Even if the mass of magma does exist, but the massive eruption will not happen in the near future. Of course we do not expect the paroxysmal eruption of the Toba supervolcano, even if it can stop the phenomenon of global warming phenomenon is happening lately.

sumut-srtm1

SRTM image of North Sumatra with key locations referred to in this article

In Indonesia Geographic Expedition VI in 2009 in the province of North Sumatra, Toba tuff observed when the majority of the teams entered an exclusive area on the shores of Lake Toba in brand named Taman Simalem Resort. The place berdisain luxurious and chic, with a plaza just facing the beautiful Lake Toba northwest. Where previously the status of protected forest has been transformed into expensive tourist areas, including the construction of the temple which is close to completion.

Slopes of the plateau occurred at Toba in Brand cut and stockpiled (cut and fill) into a pattern of winding streets produce exotic scenery. Vihara placed at one end of the cape and flanked by steep slopes. This is where problems will arise. Steep slopes dominated by Toba tuff is loose and sandy, and prone to denudation. The symptoms of erosion and avalanches have started to appear. Developers seem to understand properly the problems to be faced. Some of the retaining walls and gabion stone are built to withstand the instability of slopes. Maintenance that will constantly have controlled so that it will be very expensive.

Another Toba tuff outcrop on the road toward Sidikalang, through SUMBUL. SUMBUL lies exactly on a line extending morphology northwest – southeast as an expression of the Great Sumatran Fault. This line is occupied by the flow Lau Renun the sharp notch river valley. On the steep slopes Renun Lau, Toba tuff hard as stone material excavated foundations. Meanwhile, in the direction opposite ends in Doloksanggul – Onanganjang, most of tuff rock has undergone alteration. Soil yellow, orange, and red adorn the roadside due to the influence of magma in the process the remaining solution further.

On the island of Samosir, Toba tuff which is hard to be artifacts of the ancient kingdoms relics of Batak in the form of chairs and tables altar where torture captured enemy. The stones are very famous as a seat attractions in Siallagan, Simanindo District. Hard tuff stone is also a sarcophagus, a place to store the bodies of kings Sidabutar in Tomok, or idols. Toba tuff that when fired destroy the surrounding ecosystem, long after it apparently played a role in the development of culture Batak old kingdoms around Lake Toba and Samosir.

High levels of violence Toba tuff rocks are not only found on the slopes Lau Renun, Sidikalang, Dairi, or on the island of Samosir, but also reflected a very high waterfall and vertical Sipisopiso in Brand. Especially along the slopes are very steep gorge between Siguragura Sei Asahan and Appliances, District Porsea, Toba Samosir, Toba tuff rock glance looks like granite that need several times a powerful punch with a geological hammer to break it.

Sei Asahan as river drainage and where it comes out of Lake Toba is a maximum of 905 m above sea berpermukaan, eroded vertically and in Toba tuff rock follow the pattern of tectonic cracks. Tributaries into the valley Asahan as high waterfalls, outlines the water turns when the dew falls straight down the canyon walls. Sei Asahan stream leading to the northeast and then turn into a large river in Perhitian, Halado, once all the water out of the tunnel hydropower Stairs. The river eventually flows bermeander on the plains of the east coast of North Sumatra, to then empties as distributary rivers that meander in the delta environment in Teluk Nibung, Tanjungbalai. This place is a bustling harbor which becomes the Strait of Malacca to the boats for Selangor, Malaysia.

Four sheets of the geological map around Lake Toba clearly mapped distribution of this Toba tuff (Aldiss et al., 1983, Aspden et al. 2007, Cameron et al., 1982, and Clarke et al. 1982). Toba Tuff spread far to the north, and found to Pematangsiantar, even reaching Tebingtinggi. No need to wonder. If in the middle of the Indian Ocean might be found Toba tuff deposition, the distance to reach Tebingtinggi just not much for a super-powerful eruption. To the south, tuff sediment filled hills and valleys along Bukitbarisan since Sidikalang Mountains in the northwest to Tarutung and Sipirok in the southeast and south.

Tarutung is a small town that is very well known by researchers geoscience, particularly those engaged in the field of earthquake disasters. Place in Batak language means “durian” have been shaken by an earthquake of 6.6 on the Richter scale damage on 27 April 1987. It is the path in Bukitbarisan it is the fault line and active fault along Sumatra island, ranging from the Gulf Semangko in Lampung, continuous to the north through Bengkulu, Kerinci in Jambi, Lake Batur and Padang Panjang in West Sumatra, Tarutung – Sidikalang in North Sumatra, to Bandaaceh.

Morphological features valleys and hills extending as a result of active tectonic activity, evident in Tarutung, where Aek Sigeaon flows along the valley. Active tectonic activities which destroy rock strength also affect the condition of the road between Tarutung and Sipirok. Aek Latong, roads always ambles. Besides being located on active fault lines, plus there is the influence of clay stone is broken down and prone to landslides.

Cracks formed along the valley is also a way for the hot water discharge. Sipoholon hot springs near the measured temperature Tarutung 63,8oC become a bustling tourist spot. Sipoholon hot water out of the crevices of rocks and penetrate the Toba tuff. The precipitate formed by travertine hot water breaks Toba tuff produce precipitates with interesting patterns, such as the formation of stalactites and stalagmites, as well as the deposition of travertine terraces.

To the southeast is still found spring water with air bubbles with a slightly sour taste so people call it “soda water” in Parbubu. The water temperature is generally relatively warm, which 31,5oC. But because the air temperature is also quite hot (30,7oC), soda water Parbubu feels cold to the touch. The more to the southeast, in Sipirok, also found the hot springs in Aek Milas Sosopan utilized by the local mosque as wudlu water. Aek Milas in Batak language Sipirok indeed means “hot water.”

The hot springs along Tarutung – Sipirok the hot springs that occur as a result of the fault, even hot springs are thought to originate from sources magmatis well. It is different with the hot water temperature 47,3oC that ache in the teeth because it is very acidic pH in Aek Rangat located on the slopes of Mt. Pusukbuhit, near the island. Hot water is very clear in Aek Rangat directly related to volcanic activity Pusukbuhit, as well as hot water also appear at Lau Sidebukdebuk, on the slopes of Mt. Sibayak, Tanah Karo

Land Batak Beautiful

At the end of the expedition exploring the history of Lake Toba eruption is exceptional as well as products tufnya widespread, the impression gained is awe landscape formed by natural processes, the processes of geological, tectonic and volcanic lasted berribu- thousand years. Lake, plateau, mountains, hills, valleys, and rivers, and forests, plantations and its people, North Sumatra entirely natural compile into a beautiful harmony of nature. It is suitable meanings as buts nauli Tapanuli, beautiful land. Let outsiders who roams just 10 days in North Sumatra, a native of Batak still always amazed with the land of their birth.
How to love the Batak against his native land, always exemplified when a Batak sang “O Tano Batak” (1933) written by S. Dis (Siddik Sitompul, 1904-1974) with most of the lyrics are as follows:

O Tano Batak halolonganhu …
O Tano Batak sinaeng hutahap,
dapot honon hu, tano hagodangan hi
(Oh Batak who always longed for … Oh Land Batak always I looked up, I want always to return home to the land of birth).
How hard character of the Batak, his eyes glazed, maybe even sobbing, while singing the song. Moreover, when did this sense of homesickness while away wander.

O Tano Batak, I have always wanted to get back your beauty …
book

Aldiss, D.T., S.A. R. Whandojo, Sjaefudien A.G., and Kusjono (1983), Geologic Map of the Sidikalang Quadrangle, Sumatra 0618, Scale 1:250,000, Geo. Res. And Dev. Centre, Bandung.
Aspden, J.A., W. Kartawa, D.T. Aldiss, A. Djunuddin, D. Diatma, M.C.G. Clarke, R. Whandoyo, and H. Harahap (2007), Geologic Map of the Padangsidempuan and Sibolga Quadrangle, Sumatra 0717, Scale 1:250,000, Geo. Res. And Dev. Centre, Bandung.
Bemmelen, R.W. van (1949), The Geology of Indonesia, Vol. IA, Martinus Nijhoff, The Hague, The Netherlands.
Cameron, N.R., J.A. Aspden, D. McC Bridge, A. Djunuddin, S.A. Ghazali, H. Harahap, Hariwidjaja, S. Johari, W. Kartawa, W. Keats, H. Ngabito, N.M.S. Rock and R. Whandoyo (1982), Geologic Map of the Medan Quadrangle, Sumatra 0619, Scale 1:250,000, Geo. Res. And Dev. Centre, Bandung.
Clarke, M.C.G., S.A. Ghazali, H. Harahap, Kusyono, and B. Stephenson (1982), Geologic Map of the Pematangsiantar Quadrangle 0718 Scale 1:250,000, Geo. Res. And Dev. Centre, Bandung.
Oppenheimer, C. (2002), Limited Global Change Due to the Largest Quaternary Eruption Toba 74kyr BP, Quat. Sci. Rev. 21 (14-15), pp. 1593-1609.
Rampino, M.R., dan S. Self (1993), Climate-Volcanism Feedback and the Toba Eruption of ~ 74,000 Years Ago, Quaternary Research, Vol. 40, pp. 269-280.
Verstappen, H.Th. (2000), Outline of the Geomorphology of Indonesia, A Case Study on Tropical Geomorphology of a Tectogene Region, ITC, Enschede, the Netherlands.

Ditulis oleh : Dr.Ir. Budi Brahmantyo, M.Sc (Anggota KK Geologi Terapan http://blog.fitb.itb.ac.id/BBrahmtyo)