Oldoinyo Lengai is an active carbonatite volcano in Tanzania., UPSC.

Description

Ol Doinyo Lengai volcano

Context: Tanzania's outlandish Ol Doinyo Lengai volcano, the only volcano on Earth that is currently erupting carbonatite lava, has been sinking at a rate of 1.4 inches per year for the past decade.

Name	Ol Doinyo Lengai.
Local Name	Mountain of God.
Country	Tanzania, Africa.
Formation	In response to the development of the East African Rift system, a divergent plate boundary. The volcano is part of the Ngorongoro volcanic highland, a system of volcanoes that were active from the Miocene to present.
Landform	Composite.
Volcano Type	Stratovolcano.
Elevation	2,962 m (9,718 ft).
Characteristics	Light-colored ash cone and crater. Numerous side vents that surround its cone. Active and ephemeral stream channels, feeding into Lake Natron. It is the only active volcano known to emit natrocarbonatites, a rare type of volcanic rock that is rich in sodium, potassium, and calcium carbonate, but low in silica about less than 25% silica by weight.
Recent Finding	Ground around the summit of Ol Doinyo Lengai volcano, which sits along an active rift zone in East Africa, subsided at a rate of 1.4 inches (3.6 centimeters) per year between 2013 and 2023. The likely cause for this sinking volcano was the deflating magma reservoir, which is located 3,300 feet (1,000 m) under the volcano. The data collected from two satellite systems, Sentinel-1 and Cosmo-SkyMed.

Volcanoes and Volcanic Landforms

A volcano is a place where materials such as gases, ashes and/or molten rock material – lava – escape to the ground from the interior of the Earth.

Type of volcanoes based on the frequency of Eruption

Active Volcanoes

A volcano is called an active volcano if the materials mentioned are being released or have been released out in the recent past. Example: Kilauea Volcano, Hawaii island.
Most known volcanic activity occurs along converging plate margins and mid-oceanic ridges.

Dormant Volcanoes

These are not extinct but have not erupted in recent history.
The dormant volcanoes may erupt in future.
Example:Mount Kilimanjaro, Tanzania.

Extinct volcanoes

These have not erupted in the distant geological past. Example: Dhinodhar Hill, Gujarat.

From where do these materials come?

The layer below the solid crust is mantle.
It has higher density than that of the crust.
The mantle contains a weaker zone called asthenosphere.
It is from this that the molten rock materials find their way to the surface.

Difference between Lava and Magma

The material in the upper mantle portion is called magma.
Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.

Material composition

The material that reaches the ground includes lava flows, pyroclastic debris, volcanic bombs, ash and dust and gases such as nitrogen compounds, sulphur compounds and minor amounts of chlorene, hydrogen and argon.

Type of volcanoes based on nature of eruption

Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.

Shield Volcanoes

Barring the basalt flows, the shield volcanoes are the largest of all the volcanoes on the earth.
The Hawaiian volcanoes are the most famous examples.
These volcanoes are mostly made up of basalt, a type of lava that is very fluid when erupted.
For this reason, these volcanoes are not steep.
They become explosive if somehow water gets into the vent; otherwise, they are characterised by low-explosivity.
The upcoming lava moves in the form of a fountain and throws out the cone at the top of the vent and develops into cinder cone.

Examples: Barrier (Kenya), Erta Ale (Ethiopia), Mount Nyamuragira (Democratic Republic of the Congo), Mauna Loa, Hawaii.

Composite Volcanoes

These volcanoes are characterized by eruptions of cooler and more viscous lavas than basalt.
These volcanoes often result in explosive eruptions.
Along with lava, large quantities of pyroclastic material and ashes find their way to the ground.
This material accumulates in the vicinity of the vent openings leading to formation of layers, and this makes the mounts appear as composite volcanoes.

Examples: Mount Fuji in Japan and Mount Shasta in California.

Caldera

These are the most explosive of the earth’s volcanoes.
They are usually so explosive that when they erupt they tend to collapse on themselves rather than building any tall structure.
The collapsed depressions are called calderas.
Their explosiveness indicates that the magma chamber supplying the lava is not only huge but is also in close vicinity.

Example: Crater Lake, in Oregon.

Flood Basalt Provinces

These volcanoes outpour highly fluid lava that flows for long distances.
Some parts of the world are covered by thousands of sq. km of thick basalt lava flows.
There can be a series of flows with some flows attaining thickness of more than 50 m.
Individual flows may extend for hundreds of km.
The Deccan Traps from India, presently covering most of the Maharashtra plateau, are a much larger flood basalt province.
It is believed that initially the trap formations covered a much larger area than the present.

Mid-Ocean Ridge Volcanoes

These volcanoes occur in the oceanic areas.
There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins.
The central portion of this ridge experiences frequent eruptions.

Volcanic Landforms

Intrusive Forms

The lava that is released during volcanic eruptions on cooling develops into igneous rocks.
The cooling may take place either on reaching the surface or also while the lava is still in the crustal portion.
Depending on the location of the cooling of the lava, igneous rocks are classified as volcanic rocks (cooling at the surface) and plutonic rocks (cooling in the crust).
The lava that cools within the crustal portions assumes different forms.
These forms are called intrusive forms.

Batholiths

A large body of magmatic material that cools in the deeper depth of the crust develops in the form of large domes.
They appear on the surface only after the denudational processes remove the overlying materials.
They cover large areas, and at times, assume depth that may be several km.
These are granitic bodies.
Batholiths are the cooled portion of magma chambers.

Lacoliths

These are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below.
It resembles the surface volcanic domes of composite volcano, only these are located at deeper depths.
It can be regarded as the localised source of lava that finds its way to the surface.
The Karnataka plateau is spotted with domal hills of granite rocks.
Most of these, now exfoliated, are examples of lacoliths or batholiths.

Lapolith, Phacolith and Sills

As and when the lava moves upwards, a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane.
It may get rested in different forms.
In case it develops into a saucer shape, concave to the sky body, it is called lapolith.
A wavy mass of intrusive rocks, at times, is found at the base of synclines or at the top of anticline in folded igneous country.
Such wavy materials have a definite conduit to source beneath in the form of magma chambers (subsequently developed as batholiths). These are called the phacoliths.
The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material.
The thinner ones are called sheets while the thick horizontal deposits are called sills.

Dykes

When the lava makes its way through cracks and the fissures developed in the land, it solidifies almost perpendicular to the ground.
It gets cooled in the same position to develop a wall-like structure.
Such structures are called dykes.
These are the most commonly found intrusive forms in the western Maharashtra area.
These are considered the feeders for the eruptions that led to the development of the Deccan traps.