On January 27, 2010, a mild earthquake occurred in Ziarat area, causing panic and alarming the locals. However, the chaos and fear was not due to the jolts and shaky ground – instead it was caused by the spewing molten rocks, steam and sparks coming out from some cracks.
The intensity of 3.9 magnitude tremor was reported in Sari near a mountain in Ziarat Valley, Balochistan. The hypocenter or underground center of the earthquake was 60km beneath.
Two geologists from the Geological Survey of Pakistan (GSP) went to the spot for field investigation. Both of them had also surveyed the area in 2008 after a mild earthquake.
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The outpour of the lava was on a small scale and most of the molten material was confined to area around the fissure or crack. The molten lava was emitted from a small scoria or volcanic cone and from four small fissures. All the fissures could be seen on Tor Zawar Mountain at Sari, Ziarat. Experts agreed that the lava may have arisen from the upper mantle or recycled from pre-existing volcanic rocks in the ‘crust’ – the top most layer of Earth.
Old lava and plate tectonics
In geological terms the area is called Bibai formation, which is exposed for 1,200km in the region. It had been thoroughly studied by GSP in 1979, 1984 and 1996.
According to scientists, these activities are very old. The rocks erupted as submarine lava flowed some 72 million years ago, south of the equator and very far from the present location. This happened during northward drift of the Indian subcontinent. These volcanic rocks initially occurred as the molten lave residing in the subsurface magma chamber.
Molten material beneath the surface is called magma and when it erupts outside it is called lava. In this case, the outpour of the lava may have been driven by explosive expanding steam resulting from cold ground water touching the hot rocks or magma at Gogai-Wam Fault Line.
The geochemistry data corresponds to re-melting of Bibai volcanics at depth under very high temperature and pressure conditions. Frictional forces along the fault zone might be one of the reasons for the recycling of pre-existing Bibai volcanoes which had formed on the slopes of sea mounts as hotspot volcanoes on submarine fan on the margin of Indo-Pak Plate.
When the Gogai Wam fault ruptured in 2008, it may have created chambers from which molten rocks rose and eventually erupted through channels in the weak zone.
Earth vibrations might have developed new cracks and enlarged pre-existing fissures; local faults may have been reactivated during recent events, causing the molten material to ooze out. The molten material from may had shot from the fault related fissure which was not vertical near surface and fed smaller lateral lava conduits down the slope. It is also likely that minor earthquakes due to subsurface movement of magma, local deformation and ground swelling in the region, may have preceded a growing volcanic outpouring.
Though the present activity is on a very limited scale, yet we have seen the beginning of an entirely new phenomenon, which at the same time is suggestive of the massive rupture beneath the surface. It also indicates that active tectonic activity and seismicity coupled with magmatism, pose a new threat to this scenic valley, unheard of before the present event.
Although there is no indication that it will explode again in the near future, small eruptions can be expected from this growing volcano for which seismic devices may be installed on the magma pipe to record tremors induced as lava moves up into the dome. Strain meters should also be installed to measure any local deformation.
* Asif Nazeer Rana is Deputy Director in Geolabs, Geological Survey of Pakistan, Islamabad.