Emi Koussi is a high pyroclastic shield

Pyroclastic shield

In volcanology, a pyroclastic shield or terrestrial ignimbrite shield is an uncommon type of shield volcano. Unlike most shield volcanoes, pyroclastic shields are formed mostly of pyroclastic and highly explosive eruptions rather than relatively fluid basaltic lava issuing from vents or fissures on...

 volcano

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 that lies at the south end of the Tibesti Mountains

Tibesti Mountains

The Tibesti Mountains are a range of inactive volcanoes located on the northern edge of the Chad Basin in the Borkou- and Tibesti Region of northern Chad. The massif is one of the most prominent features of the Central-Sahara desert and covers an area of approximately 100,000 km². The northern...

 in the central Sahara

Sahara

The Sahara is the world's second largest desert, after Antarctica. At over , it covers most of Northern Africa, making it almost as large as Europe or the United States. The Sahara stretches from the Red Sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic Ocean...

 of northern Chad

Chad

Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...

. It is the highest mountain in Chad, and the highest in the Sahara. The volcano is one of several in the Tibesti massif, and reaches 3445 m in altitude, rising 2.3 km above the surrounding sandstone plains. The volcano is 60 by 80 km wide.

Two nested caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

s cap the volcano, the outer one being about 12 by 15 km in size. Within it on the southeast side is a smaller caldera, about 2–3 km wide and 350 m deep. Numerous lava dome

Lava dome

|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...

s, cinder cone

Cinder cone

According to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...

s, maar

Maar

A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...

s, and lava flows are found both within the calderas and along the outer flanks of the shield. The inner caldera contains large natron

Natron

Natron is a naturally occurring mixture of sodium carbonate decahydrate and about 17% sodium bicarbonate along with small quantities of household salt and sodium sulfate. Natron is white to colourless when pure, varying to gray or yellow with impurities...

 deposits which see some harvesting for domestic animal salt lick

Salt lick

A mineral lick is a natural mineral deposit where animals in nutrient-poor ecosystems can obtain essential mineral nutrients...

 use by the local people.

Emi Koussi has been used as a close analog to the famous Martian

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 volcano Elysium Mons

Elysium Mons

Elysium Mons is a volcano on Mars located in the Elysium Planitia, at , in the Martian eastern hemisphere. It stands about 13.9 km above the surrounding lava plains, and about 16 km above the Martian datum. Its diameter is about 240 km, with a summit caldera about 14 km across...

. One of the most important morphological differences between volcanoes on Mars

Mars

Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 and Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 is the widespread furrowing of the surface due to flowing water on terrestrial

Terrestrial

Terrestrial refers to things related to land or the planet Earth.Terrestrial may also refer to:* Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to in trees etc.** A fishing fly that simulates the...

 volcanoes. The furrows are shallow valleys. Larger channels have a different origin. Major channels can be seen on volcanoes on both planets and indicate low points in caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 rims where lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

spilled out of pre-collapse craters.