The East African Rift Valley was created about 25 million years ago as a divergent (moving away from each other) tectonic plate boundary formed as the Somalian plate moves away from the Nubian plate.
The East African Rift (EAR) Valley, noted by Astronauts, is the most significant physical detail on the Earth’s surface from space. Our continental lithosphere (Earth’s crust and upper mantle) is typically 93 miles (150km) thick! The formation of the Rift thinned the continental lithosphere to about 12 miles thick, producing 30 active volcanoes in the area, such as the well know Mount Kilimanjaro. Of these active volcanoes, ONE is very special.
The Ol Doinyo Lengai, meaning “Mountain of God” and located in Tanzania, claim to fame, is being the only natrocarbonatite volcano in the world. The lava that erupts from Ol Doinyo Lengai is at a cool temperature of 1,000°F! Magma, being a complex fluid, ranges in temperature from 1300°F to 2400°F and most lava is comprised of silicate (silicon-oxygen compound) mixtures. The lava of this peculiar volcano erupts as a pitch-black fluid (no classic orange glow) and cools quickly to a stark white mineral.
So let’s break this down:
* Pure Calcium, housed in Argon gas due to its reactivity with atmospheric water
Silicon is a basic component in rock forming minerals (roughly 28% by weight) and silicate minerals compose of over 90% of Earth’s Crust! Sand and quartz are the purest form of silicates, SiO₂.
Carbonatites are a rare type of rock that is greater than 50% carbonate materials and less than 10% Silicon minerals. Nyerereite/Na₂Ca(CO₃)₂ and Gregoryite/Na₂K₂Ca(CO₃)₂ are the two main types of natrocarbonatite. (Natro meaning sodium, Na)
Carbonates: Two main types- limestone/CaCO₃ and dolomite/CaMg(CO₃)₂, with a type of pure limestone being chalk.
Most of the carbonate rocks we know are sedimentary in nature, meaning they were laid down in intercontinental shallow oceans, on a continental shelf, or on dry land, making them part of the Crust, a ridged material, during the Cambrian and Ordovician periods of the Paleozoic Era, about 541 million years ago.
*Bryce Canyon's Sedimentary Rock (Side Note: When Visiting Bryce, the Park Ranger refers to the landform in its proper name. Bryce Eroded Plateau)
Carbonatites carbon isotope is more indictive of a mantle rock, which “flows” from convection, or heat transferred from the interior of the Earth to the surface.
A small section of the upper mantle is molten. This allows movement of tectonic plates.
Carbonatites are rare and peculiar, as during the partial melt (within the molten upper mantle) they become immiscible (think oil and water) with the more abundant silicate materials.
Calcium density is almost half of Silicon, making it significantly lighter than the surrounding partial molten materials, creating Fractional Crystallization, one of the most important processes of the Earth’s lithosphere.
So, with all these mechanisms acting together, the most unique volcano on our planet erupts with low viscosity (the ability to flow, for example, corn syrup is highly viscose) and runs down the volcanic cone like water. Shield volcanoes, like those of the Hawaiian Island chain have low viscose lava, gently flowing out because trapped gas has been released, while Mount St. Helens had a highly viscose magma with trapped gases which is why she exploded violently. Ol Doniya Lengai, again is special, because while the carbonatite magma is very low viscosity (like in Hawaii) there is an abundance of dissolved carbon dioxide (like Mount St. Helens), causing a garden hose effect of sputtering before flowing like a waterfall.
*Continental Rift Volcanism with a Mantle Plume
Another very interesting physical aspect of Ol Doniya Lengai, is the carbonatite materials exhibit hygroscopic (water loving) and anhydrous (no water) traits. Nyerereite is very hygroscopic and becomes hydrated (surrounded by water molecules) when the magma reaches the surface allowing the lava to flow like water. Gregoryite, being anhydrous, quickly cools the lava within hours or days to a bright white material.
Our planet is so very interesting!
Until next time, Xo.