oldoinyo1_copy.jpg
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Written by: Sylvie La

Introduction
Volcanoes come in different sizes, shapes, contain different types of magma, and have different types of explosions. This page will focus on attributes of a special type of volcano.

Volcanoes are some of the most destructive and awe striking natural features on the planet. These dominating structures can be broken into five main categories, each with specific features:
Type of Volcano
Shape
Type of Magma
Typical Eruption Type
Shield
Great width compared to height
Basalt
Hawaiian
Cinder Cone
Conical, low pile of loose cinders
Basalt
Strombolian
Stratovolcano
Gentle slopes at base, steep near summit
Andesite
Vulcanian -> Plinian
Lava Dome
Bubble-like dome of magma
Rhyolite
Vulcanian
Caldera
Circular depression with central elevated mass
Rhyolite
Plinian
As the table suggests, a Stratovolcano typically has violet eruptions with mid to high viscosity magma. Oldoinyo Lengai in Africa is just such a volcano, but with different types of eruptions.
Origin of Name
The Maasai tribe who live nearby this unique volcano gave its name, Oldoinyo Lengai. It is translated from the Maasai people's language meaning, "Mountain of God." (4)

Where did it occur?
The Oldoinyo Lengai volcano is in Tanzania, Africa, which is located on the east side of the continent. In Figure 1, the map shows that there are other volcanoes nearby
.
Figure 1: Oldoinyo Lengai along with other volcanos are plotted northern of Tanzania. (http://www.swisseduc.ch/stromboli/perm/lengai/icons/lengmap.gif)
Figure 1: Oldoinyo Lengai along with other volcanos are plotted northern of Tanzania. (http://www.swisseduc.ch/stromboli/perm/lengai/icons/lengmap.gif)


What type of event was it?

Oldoinyo Lengai is a stratovolcano, which is the most common type of volcano. At first glance, it is presumed as just a mountain because of its high altitude of about 2886m (9524ft). (4) Figure 2 shows a top view of the volcano. The areas that are shaded in gray are hornitos, which are "rootless spatter cones." Lava is pushed up through an opening surface then collects around the opening which creates a steep, stacked cone. "They are 'rootless' because they are fed by lava from the underlying flow instead of from a deeper magma conduit." (8) Like any other stratovolcanoes, the Mountain of God is symmetrical and has a conical shape. Figure 3 shows a side view that portrays that lava has overflown and topple down the sides. There are several layers that make up the volcano such as pyroclastic debris and solidified lava flows. Stratovolcanoes are stronger than cinder cone volcanoes because they have solidified lava that acts as glue which holds the volcano together. As a stratovolcano, there is a broad range of hazards that it produces such as landslides, flank failures, volcanic storms, and ash flows. The volatile abundance of the volcano is moderate to high, which means that it releases gases that are harmful.
Figure 2: Hornitos are mapped out on the floor of the crater. (http://www.v-e-i.de/pictures/tan/lengmap606.jpg)
Figure 2: Hornitos are mapped out on the floor of the crater. (http://www.v-e-i.de/pictures/tan/lengmap606.jpg)
Figure 3: Hornitos are clearly seen as steep cones on the floor of the crater. Photo was taken by: Tom Pfeiffer (http://decadevolcano.net/photos/africa/oldoinyo_lengai/lengai_0803/lengai_34632.jpg)
Figure 3: Hornitos are clearly seen as steep cones on the floor of the crater. Photo was taken by: Tom Pfeiffer (http://decadevolcano.net/photos/africa/oldoinyo_lengai/lengai_0803/lengai_34632.jpg)


The volume of the eruption is moderate because of the type of explosion it produces. There are two types of eruptions that the stratovolcano produces. First is a vulcanian type of eruption, the early stage, which consists of viscous magma and gas. It is only the first stage because the volcano is clearing out its vent by blowing out pyroclastics and ash. Second is a plinian type of eruption, the final stage, which has a large volume of ash that explodes in a column and can reach up to 45km high. It is more explosive and powerful than the vulcanian eruption. The plinian eruptions do not always have to occur after vulcanian eruptions.

When did it occur?
The volcano's first eruptions have been dated back to about 1550 B.C., give or take 1000 years. Since then, there might have been eruptions that occurred in 50, 700, and 1350 A.D. There are records that show eruptions have occurred in 1880, 1882, 1904, 1907, 1914, 1916, 1926, 1940, 1954, 1955, 1958, 1960, 1967, 1994, 2006, and 2007-ongoing. In 1921, there are records of mudflows, also known as lahars.
(2) Since the volcano is so high in altitude, there can be snow. When an eruption happens, the hot ash melts the ice and snow causing it to create mud, which flows down the sides like hot cement. In 1966 and 1967 there were explosive eruptions that created a crater of ash, and in 1983, there was visible evidence that the volcano was being filled with lava. Over the years, the lava has spilled over the top creating layers upon layers on the volcano.

In September 2007, there was an explosive eruption that sent a cloud of ash southward. The image below in Figure 4 is from NASA. It provides a clear illustration of the direction where the cloud of ash covers.
(6) Wherever the wind carries the ashes, it covers the region in darkness. In the photo below, the region south of the volcano will be dark due to the large volume of ash that was exploded. (1)
Figure 4: Ash from a recent eruption is headed south due to the direction of the wind. (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=19113)
Figure 4: Ash from a recent eruption is headed south due to the direction of the wind. (http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=19113)


What were its consequences?
According to the people who did research at Oldoinyo Lengai, they recorded reactions from people who lived in the area. In 2006 there was an eruption that caused 3,000 people to flee their homes. The rumbling from the eruption created fear, the smoke coming from the volcano caused panic, and the lava flow coming down the volcano caused even more panic. Apparently, eruptions happen every year. eruptions have destroyed communities, vegetation, and polluted residents' water sources. In 2007's eruption, rocks were propelling down to the villages and injured a few people. (5)



Uniqueness of the Oldoinyo Lengai Volcano
One characteristic that makes Oldoinyo Lengai different from other stratovolcanoes is that it has a low viscosity which makes it a fluid-like lava. The major attribute that highlights this volcano as unique is that it is the only volcano on Earth that produces natrocarbonatite lava. Natrocarbonatite is is made up of two minerals. The minerals contain an abundant amount of sodium and potassium which contain no water. The minerals easily and quickly reacts to the moisture in the atmosphere. An interesting fact about the natrocarbonatite substance is that is much cooler at 500-600 degrees Celsius (930-1,100 degrees Fahrenheit ) than the silicate lava at 700-1,200 degrees Celsius (1,300-2,200 degrees Fahrenheit). The flowing natrocarbonatite lava appears to be a dark, mud-like color, but lightens to an almost white after the lava has been exposed to the atmosphere for a few months. As in Figure 5, it illustrates a contrast between the fresh dark lava and cooled white lava. If it rains, the lava may quickly turn white. Since it is natrocarbonatite lava, only at night can the dark red glow from the volcano can be seen like in Figure 6. (6)
Figure 5: Fresh and old lava going down a stream. (http://blogs.stlawu.edu/lengai/files/2009/05/p270994-10-300x203.gif)
Figure 5: Fresh and old lava going down a stream. (http://blogs.stlawu.edu/lengai/files/2009/05/p270994-10-300x203.gif)
Figure 6: A calm eruption from a hornito. (http://www.v-e-i.de/pictures/tan/lengm0604.jpg)
Figure 6: A calm eruption from a hornito. (http://www.v-e-i.de/pictures/tan/lengm0604.jpg)

This stratovolcano produces not only vulcanian and plinian eruptions but also lava fountains, strombolian eruptions, aa and pahoehoe flows. (3)

The short clip below shows Oldoinyo Lengai spilling out its natrocarbontite lava. It is peaceful enough for people to come close to it but dangerous enough to keep a cautious distance. As stated before, unlike other stratovolcanoes, this one has a low viscosity which allows the magma to flow like water. The erupting lava follows in a stream that was created from other lava flows.



Conclusion: Hazard Mitigations
Whatever the type of volcano, is it essential to acknowledge the hazards if you live by one. Villagers near the Oldoinyo Lengai volcano such as the Maasai tribe need to be aware and educated about efficient evacuation plans, how to protect water sources, and installments of monitoring equipment. (7) Preparation and awareness for any kind of natural disaster can increase your safety.


Sources

1) Belton, Fredrick A. Ol Doinyo Lengai. 5 Nov. 2009. Web. 17 Feb. 2010. <http://frank.mtsu.edu/~fbelton/lengai.html>.

2) Global Volcanism Program. Web. 4 March 2010. <http://www.volcano.si.edu/world/volcano.cfm?vnum=0202-12=&volpage=erupt>.

3) Roscoe, Richard. Oldoinyo Lengai Volcano. Web. 4 March 2010. <http://www.photovolcanica.com/VolcanoInfo/Oldoinyo%20Lengai/Oldoinyo%20Lengai.html>.

4) Oldoinyo Lengai: A Unique Volcano. Web. 11 Feb. 2010. <http://blogs.stlawu.edu/lengai/>.


5) Oldoinyo Lengai Project. 2009. Web. 17 Feb. 2010. <http://www.v-e-i.de/vhdl/project/pleng.html>.

6) Simmons, Robert. Earth Observatory. NASA.18 Sep. 2009. Web. 17 Feb. 2010. <http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=40217>.

7) USGS Newsroom. "Tanzanian VillagersEnvouraged to Learn Hazards of Living Near Eruptong Volcano." 5 March 2009. Web. 5 March 2010. <http://www.usgs.gov/newsroom/article.asp?ID=2159&from=rss>.

8) Volcanic Geyser: Volcano Terms and Definition. Web. 4 March 2010. <http://volcano-pictures.info/glossary/hornito.html>.