Natural Hazards and Disasters: Volcano of the Week!

27/01/2014-02/02/2014

This week’s volcano of the week is:

Oldonyo Lengai

Location: Tanzania, East Africa

Type: Stratovolcano

Elevation: 2962m, 9715 ft

Last Eruption: 2013

Status: Active

Details:

Ol Doinyo Lengai, known as the ‘Mountain of God’ in Masai is the only active volcano in Tanzania located in the north of the country, in the region of north Arusha.

It is well known for its carbonatite lava and tephra that occur during eruptions and is the only volcano in the world that is known to do so. Carbonatite lavas are unique compared to other types of lava; hardly contain any silicon, are very fluid and have temperatures of only 510° Celsius compared to temperatures of over 1100° Celsius. It also glows orange at night but is black or brown in daylight and turns white when it comes in contact with water.

The volcano is conical in shape and has two craters on the summit; a southern one which is inactive and a northern active crater which measures approximately 700 yards. Pyroclastic and ash cones, explosion craters such as Shallow Crater and Loluni Crater and tuffs also occupy the volcanic landscape on the northern, southern and eastern flanks on the main volcano cone at various heights.

Activity is mainly centred on the main vents in the southern crater known as ‘Devil’s Needle’ and the number of cones found in the crater which are a result of past eruptions. The morphology of the northern crater has continuously been changing as a result of eruptions, causing it to increase or decrease in depth and steepness of crater walls as well as resulting in a number of ash and pyroclastic cones.

Numerous volcanic activities have occurred on Ol Doinyo Lengai from as early as 1880 to the last recorded one being in 2013. The activities have ranged between VEI 0 to 3; most being effusive and strombolian in nature and not causing damage. There have been a few exceptions to this, for example; in 1917 an eruption on Ol Doinyo Lengai caused the vegetation on the mountain to be entirely destroyed and led to the contamination of water, destruction of grazing land and loss of cattle that belonged to the local Masai tribes due to the widespread ash caused by the eruption.

Volcanic hazards such as lava, bombs, ash, tephra, lapilli and gas are hazards often associated with eruptions of Ol Doinyo Lengai and evidence of these exist on the volcano and the surrounding region.

Eruptions such as the ones between 1940 and 1941 caused tephra to be distributed over large distances such as 60 miles from the centre of the volcano. Large volumes of volcanic gases were also erupted during these eruptions and tephra and bombs were thrown from thirty to forty feet into the air. The distribution of these varies greatly. Most hazards such as bombs and tephra are found in the crater or the immediate area surrounding the main eruption centre and the distribution of lava flows also varies from the crater to the flanks of the volcano.

In July, August and October 2005 eruption; lava flows ‘natrocarbonatites’, ‘aa’ and ‘pahoehoe’ in nature (flowing at rates of 0.5 metres cubed per second in July) were reported to have taken place; flowing to the east and erupting in the north crater as well as eruptions of volcanic gas and lapilli, mainly from the centre of the north crater (0.5 metres in depth). Various cones in the crater of Ol Doinyo Lengai (a range of locations) were also reported to vary in height, some such as the cone labelled T49B in the centre of the crater had grown during the activity reaching up to 15 metres in height and is the tallest feature in the north crater. Further lava eruptions were reported in 2013.

This volcano continues showing signs of activity and erupting numerous times. Although not causing major threats to the local population, injuries have been reported caused during eruptions to the scientists and visiting tourists present in the crater during eruptions. The volcano’s activity is also known to produce earthquakes which are felt across northern Tanzania.