Sinabung Volcano (Gunung Sinabung)

Sinabung volcano (2451m) is an andesitic volcano built up of layers of viscous lava flows and lava domes together with deposits from pyroclastic flows and surges associated with lava effusion. Four craters trending in a N-S orientation are found at the summit, the last of which (crater IV) essentially forming a scar on the upper SSE flank of the volcano. In 2010, activity was focussed on craters III and IV. The dome building occurring since the end of 2013 is also in this sector and results in pyroclastic flows being directed towards the southeast.

Large pyroclastic flow	Pyroclastic flow at night

Sinabung appears to have been largely inactive for over a thousand years since the most recent pyroclastic flow deposits on the SE flank near Bekerah village could be dated at about 1100 years old. The commonly propagated misconception in the press that the last eruption was 400 years ago, appears to derive from the classification of Indonesian volcanoes according to date of most recent activity. Sinabung had been classified as having not been active for 400 years in the sense that no activity had been documented in this period. However, this merely sets the minimum time since the last eruption, not a specific eruption date. The current eruptive cycle commenced in 2010 with several phreatic explosive eruptions resulting in ash clouds beyond 5 km above sea level. The 2010 eruptions are documented by Sutawidjaja et al. 2013 (Indones. J. Geol. 8(1), p.55-61). The ash was essentially composed of mobilized highly altered (non-juvenile material) and was erupted from both craters III and IV, resulting in two adjacent but distinct ash columns as material was forced out either side of an existing dome complex.

First evacuations were ordered around the volcano in 2010. Activity then declined until the volcano reawakened in September 2013 and activity increased over the following months. By the end of 2013, growth of a small lava dome could be observed in the summit region. An overhanging lava lobe developed on the SE side of the dome where a valley offers no topological constraint. Large pyroclastic flows resulting from collapses of parts of this lobe started to descend to the base of the volcanic ediface in January 2014. Flows of up to around 6 km have resulted in a devastation zone to the SE of the volcano.

Towards the end of January, PF activity was lower than during the 13-14 January peak documented on this page and a huge 800 m long and in places at least 50m thick viscous lava flow descended the ravine that had been channelling the pyroclastic flows.

Sadly, large pyroclastic flows on February 1, 2014 claimed about 15 lives, largely of people wanting to view actiivity at the volcano. Surges detached from a large flow in a corner and swept to a nearby road about 4km from the summit.

During February and March 2014, a large andesitic lava flow was emplaced on the SE flank of Sinabung. This prominent feature is documented further down on this page.

Dome growth, pyroclastic flows and explosions continue through to the end of 2015 (last page update)

View from east at night with incandescent lava lobe	Lava lobe under extrusive vent

According to Yoshimoto et al. 2013 (IAVCEI Conference 2013, Kagoshima, Japan, Poster 4W_4D-P14), Sinabung is younger than nearby Toba Caldera and its development can be considered to have occured in two distinct phases. The older phase, largely forming the western part of todays ediface, is composed of lava flows of porphyritic andesites, whilst the younger stage, forming the eastern part of the ediface and the summit domes is composed of lava flows and pyroclastic deposits of porphyritic basaltic-andesite to andesite (Note: Cameron et al. previously suggested that Sinabung was andesitic to dacitic (Geol. Map of Medan Quadrangle, Sumatra, 1982)). The presence of mafic enclaves in the lavas suggest magma mixing in the run-up to eruptions. No, deposits could be found which could be associated with Sub-Plinian or even Plinian eruptions, suggesting that such violent events may not have occured so far in the eruptive history of the volcano.

Much like nearby Sibayak volcano (see Visitor Information section), Sinabung has in the recent past been the site of sulfur mining operations, since the solfataric activity appears to have been persistent in all summit craters during the intereruptive period, and formed sublimate sulfur deposits.

Documentation of Viscous Flow and Lobe Collapse

Extrusion of lava from Sinabung lava dome feeds a SE-oriented extrusion lobe which is effectively a highly viscous slow-moving lava flow. The volcano has yet to build a significant-sized dome such as seen at Soufriere Hills, Shiveluch, Chaiten or Paluweh, to name but a few examples. The narrow summit region is indeed unlikely to be able to support such a large structure. Activity is similar to that sometimes observed at Colima in Mexico.

During the observation period, the lobe largely appeared to be relatively static, yet it was possible to observe motion of the lobe during the build-up to a lobe collapse. Further, the lobe collapse could be observed in rare detail thanks to unusually clear weather at the time.

ANIMATION OF LAVA LOBE MOTION AND COLLAPSE RESULTING IN PYROCLASTIC FLOW:

Lobe prior to collapse	Lobe during collapse

ANIMATION OF NIGHTTIME PYROCASTIC FLOW AND EXTRUSION LOBE COLLAPSE:

Pyroclastic Flows

Break-off of material at the front of the extrusion lobe results in rockfalls and pyroclastic flows. Numerous flows could be documented during the visit to the volcano from 12-18 January 2014, which included a period of unusually intense activity on January 14.

	Pyroclastic flow in sunlight

	Tornadoes (Large Ash Devils) generated on hot PF deposits

VIDEO OF PYROCLASTIC FLOW FOLLOWED BY TORNADOES:

Nighttime Pyroclastic Flow Activity (Sometimes Accompanied by Lightning)

During the night, the incandescent material at the base of pyroclastic flows becomes visible. Larger pyroclastic flows were sometimes accompanied by static discharges (lightning). These were clearly visible at night and could be heard as short cracking noises when close to the volcano during daylight. The discharges sometimes emerged from the ash cloud or illuminated it from within. Unlike normal meteorological lightning, the discharges very short and do not appear to involve multiple use of a plasma channel.

ANIMATION OF NIGHTTIME PYROCLASTIC FLOW WITH LIGHTNING:

Static discharges (lightning) near PF flow front (Evening 14 Jan.)	Lightning near PF flow front (Evening 14 Jan.)

Triple-lobed pyroclastic flow (Evening 14 Jan.)	Pyroclastic flow with triple lightning (Evening 14 Jan.)

As PF clouds blow away incandescent deposit becomes visible	Further PF approaching fresh deposits

Pyroclastic Flow (Evening 14 Jan.)	Pyroclastic flow (Evening 14 Jan.)

Pyroclastic flow (Evening 14 Jan.)	Pyroclastic flow (Evening 14 Jan.)

Wide-angle view following series of PFs	Wide-angle view following series of PFs

Small PF during night 13-14 Jan.	Small PF during night 13-14 Jan.

Small PF during night 13-14 Jan.	Glowing lava dome during night 13-14 Jan.

Impact of Eruption on Civilisation

The lower flanks and immediate surroundings of Sinabung volcano contain farmland and a number of small villages. All farms in the pyroclastic flow field have of course been destroyed, whilst heavy ashfall, in particular downwind of the volcano during major eruptive events, has smothered crops and overloaded roof structures causing the collapse of many buildings. For example on January 10, 2014, heavy ash fall damaged villages on the NE flank of the volcano. The thin corrugated metal roofs commonly used in the area were often unable to take the load of the ash and collapsed.

Ash cloud looming over landscape	Village NE of Sinabung Volcano covered in ash

Satellite dish covered by ash and vegetation	Volcanic ash and grey landscape	Satellite dish broken by volcanic ash load

School roof collapsed by volcanic ash load	School roof collapsed by volcanic ash load, Sinabung Volcano behind

Damaged school against backdrop of heavy ash fall	Damaged school and trees

Thin corrugated roofs tear easily under weight of ash	Mosque with roof collapsed under weight of ash

Inside of collapsed house	Ash falls off steeper roofs	Collapsed roof material

Removing ash from roof	Removing ash from roof

Graveyard under volcanic ash	Shrine covered by volcanic ash	House in shadow of ashing volcano

Layer of hardened ash on roof	Pyroclastic flow descending behind village

House and trees damaged by ash fall	Cart covered by ash	House and trees damaged by ash fall

Plantation in ash at foot of Sinabung	Tree with snapped branches due to weight of ash

Papaya, Orange plants coated in ash	Lettuce coated in ash	Coffee plant bent by ash

Young orange tree bent by ash	Banana tree	Young orange tree bent by ash

Ash falls and is remobilized by wind	Palm tree folded by ash	Frog killed by ash fall

Motorbike in ash	Loudspeaker in ash

Further villages were visited which lay SE of the volcano and had been subject to recent ash fall, although with lower intensity. This villages are also directly at risk if pyroclastic flow activity intensifies.

	Village SE of Sinabung Volcano

Locals in evacuation zone are not bothered by PF in background

Satellite dishes with light smothering of ash	Pumice on roof (strange that only seen at one location but local insisted it came from eruption)

BMX bike with ash "icing" stuck in ash layer	Ash-coated motorbike

Ash-coated BMX bike, detail. Ash was virtually impossible to detach from chain.	Front wheel of ash-coated BMX bike

Cabbage coated in ash	Flowers on grave coated in ash	Crops from around volcano are unpopular

Abandoned field coated in ash	Farmers hut with PF behind

Ash-smothered field	Ash-smothered field	Field slightly further from volcano

During the visit it was apparent that a large number of locals were not respecting the exclusion zone and continued to travel in and out of it or in some cases apparently were living in the zone. This kind of situation has led to fatalities at other volcanoes such as Soufriere Hills. Many of the locals, over 20000, have however been relocated into a network of evacuation centers where the are housed and fed.

One of evacuation centers in Berestagi	Inside tent which is now home for many people

Communal kitchen	Supplies	Administration office

Recovering belongings from evacuation zone	Human activity deep in evacuation zone continues

Sinabung in 2015 (30. June - 5. July)

Activity during the observation period was low as a large lobe had collapsed in the preceeding week. The visit was thus largely used to document the changes in the structure of Sinabung, in particular the changes in the summit structure and the prominent andesite lava flow emplaced in January-March 2014. Further, the site of the fatal February 2014 pyroclastic flow was visited as was the end of the main pyroclastic flow deposit.

View from SE (Kuta Tengah)	Road Block as approach Kuta Tengah	View from SE (Kuta Tengah)

SE View. Note large andesite lava flow deposit	Summit area	Front of large andesite flow

View from SE	Andesit flow, active dome at top	View from SE

View from ESE	View from ESE of andesite lava flow

Approaching Sinabung from SSE	Roadblock SSE of Sinabung	Small pyroclastic flow

	Dome nesting on top of summit crater

Summit structure	Close-up of andesitic lava dome	Close-up taken on later date (note: small right-hand lobe is gone)

View from SSE of forest flattened by pyroclastic flows	View of main flow field from SE (flattened trees at top image)

	Small dome collapse generated pyroclastic flow

	View from SE (about 7km distance)

	View from SE (about 7km distance)

Further checkpoint as proceeding from SE to SSE viewpoints	View from location on left image

Checkpoint south of Sinabung	View over PF / Lahar flow field

River bed shaped by lahars flowing off PF flow field	Structure damaged by lahars	Structure damaged by lahars

ANIMATION OF INCANDESCENT ROCKFALL:

Nighttime observation from elevated SSE viewpoint	SSE overview	SSE overview

SSE overview, evacuated village to bottom left	Lighter deposits from recent pyroclastic flow	Lenticular cloud forming on summit

Detail of flow field looking NW	Detail of flow field looking NNW	View from main road SE of Sinabung

Location of fatal 01. Febr. 2014 pyroclastic surge. The flow followed its usual path turning left (left image), but a surge spilled outwards as it turned and reached nearby road.

Vegetation still shows signs of damage more than 1 year later	Flow bed seen through damage vegetation

	Villages in exclusion zone (theoretically evacuated)

	Ash on cars in Berestagi

Visitor Information

Sinabung volcano lies in the Toba highlands, about 10 km NW of the capital of the Karo regency, Kabanjahe, and about 50km from the major city of Medan which has over 2 million inhabitants. Medan, the capital of northern Sumatra province, has a large international airport and is the most practical starting point for visits to the volcano. Visits to Sinabung can easily be combined with visits of the Toba caldera, site of the largest known eruption in the last 25 million years. The lake which fills the caldera is 100km long and contains a large post-caldera dome complex in its midst. The lesser known Sibayak volcano, which last erupted in 1881 is also found nearby (about 10km N of Kabanjahe) and has interesting geothermal manifestations. It was also the site of minor sulfur mining operations in the past.

Main viewing hill with temporary visitor infrastructure	TV crew at one of Viewpoints

Approaching Sibayak crater	Roaring gas vent	Bubbling pool

	Crystalline Sulfur Deposits in Sibayak

Lake Toba, North end	Waterfall feeding into Lake Toba	Traditional Village near Lake Toba

Visitors should be aware that in the most recent eruptions, pyroclastic flows from Sinabung have been channelled in a SE direction towards Kabanjahe. An extremely large eruption can present a danger to inhabitants and visitors alike. On February 1, 2014, at least 15 people were killed by pyroclastic flows after entering the exclusion zone illegally. This illustrates the dangers presented by the volcano. Pyroclastic flow deposits of most previous eruptions appear to extend about 5 km from the summit in various directions, extending thus similarly to those already emplaced by the current eruptive episode. Hence, this extent can be regarded as typical for the volcano in recent times and thus unlikely to be significantly surpassed. During the 2013- eruption an exclusion zone has been established for a radius of several km around the volcano. The exact radius and further restrictions in specific areas are adapted to the activity levels at a given time. For the current situation visitors should obtain local advice in particular from the Volcano Observatory.

Monitoring the seismic data in Observatory	Thermal imaging of Sinabung

Digital seismic readout	Digital seismic readout

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