© NASA/GFSC/Arizona State University

The Moon, Earth’s closest celestial neighbour, has long fascinated scientists and space enthusiasts alike with its stark, cratered landscape. While the Moon lacks the active volcanoes found on Earth, it bears the scars and remnants of a volcanic history that spans billions of years. In this exploration, we delve into the volcanic features of the Moon, uncovering the ancient eruptions, lunar plains, and volcanic remnants that provide crucial insights into the Moon’s geological past and the broader mysteries of our solar system.

From expansive lunar maria to enigmatic volcanic domes, the Moon’s volcanic features are a testament to the dynamic and turbulent processes that once shaped this celestial body. Most of the Moon’s volcanic features are ancient, dating back billions of years to a time when the Moon was more geologically active. The lunar maria, for example, were formed around 3 to 4 billion years ago.

BASALTIC VOLCANISM

Basaltic volcanism is a geological process that involves the eruption of basaltic lava onto a planetary surface, including that of the Moon. Basaltic lava is rich in iron and magnesium and has a relatively low viscosity, allowing it to flow more easily compared to other types of lava. Basaltic volcanism has played a significant role in shaping the lunar landscape, as well as the surfaces of other planetary bodies.

LUNAR BASALT

The majority of lunar volcanic features, especially those in the lunar maria, are composed of basaltic rock. These basaltic lavas erupted onto the lunar surface billions of years ago during periods of volcanic activity.

LUNAR MARIA

The lunar maria are extensive plains on the Moon’s surface that were formed by basaltic lava flows. These plains are characterized by their relatively smooth, dark appearance and cover approximately 16% of the lunar surface. Examples include Mare Imbrium (the Sea of Rains), Mare Serenitatis (the Sea of Serenity), and Mare Tranquillitatis (the Sea of Tranquility). The lunar maria are believed to have formed as a result of large-scale volcanic eruptions that occurred between 3.1 and 3.8 billion years ago. These eruptions produced vast quantities of basaltic lava that filled impact basins and low-lying areas, creating the smooth, dark plains we see today.

LUNAR DOMES AND CINDER CONES

In addition to the maria, basaltic volcanism on the Moon also produced smaller features known as lunar domes. Lunar domes are rounded, volcanic mounds that formed from the eruption of relatively low-viscosity lava. Also, while not as common as on Earth, lunar basaltic volcanism produced cinder cones. These are cone-shaped volcanic structures formed by explosive eruptions that eject volcanic fragments, such as ash and cinders, onto the lunar surface.

RILLES

Some basaltic volcanic features on the Moon are associated with sinuous channels called rilles. These channels are thought to be the remains of ancient lava tubes or channels through which lava once flowed. Rilles can be found both in lunar maria and highland regions.

VOLCANIC VENTS

Volcanic vents on the Moon are openings in the lunar surface through which volcanic material, including lava and gases, once erupted. These vents can be found at the centers of lunar domes, cinder cones, and other volcanic features.

GEOLOGICAL ACTIVITY

The Moon’s volcanic activity has significantly declined over the eons, and it is currently considered to be volcanically dormant. However, the study of lunar basaltic volcanism provides insights into the Moon’s early history and the processes that shaped its surface.

VOLCANIC PLAINS

Lunar volcanic plains, often referred to as lunar maria (singular: mare), are extensive regions on the Moon’s surface that were formed by ancient volcanic activity. These plains are characterized by their relatively smooth, dark, and flat appearance, in contrast to the rugged and heavily cratered lunar highlands.

COMPOSITION

Lunar volcanic plains are primarily composed of basaltic rock, which is rich in iron and magnesium. Basaltic lava, with its low viscosity, flowed across the lunar surface during ancient volcanic eruptions, creating these plains.

SMOOTH APPEARANCE

One of the defining characteristics of lunar maria is their relatively smooth and dark appearance. They lack the high density of impact craters that cover the lunar highlands, making them appear more uniform.

FORMATION

Lunar maria were formed by volcanic eruptions between 3.1 and 3.8 billion years ago, during a period known as the lunar volcanic period. These eruptions resulted in vast quantities of basaltic lava flooding large-impact basins and low-lying regions on the Moon’s surface.

LUNAR DOMES

Lunar domes are small, rounded, and often symmetrically shaped volcanic features found on the Moon’s surface. These dome-like structures are the result of ancient volcanic eruptions that produced relatively low-viscosity lava, which accumulated near the eruption vent. Lunar domes offer valuable insights into the Moon’s volcanic history and the nature of volcanic activity on our celestial neighbour.

FORMATION

Lunar domes were formed by the eruption of basaltic lava onto the Moon’s surface. Unlike the violent eruptions that create large volcanic mountains or calderas, lunar domes are the result of relatively calm, non-explosive eruptions. The low-viscosity basaltic lava flows slowly from the volcanic vent and accumulates near the vent, gradually building a rounded dome shape.

CHARACTERISTICS

Lunar domes typically have a smooth, dome-like appearance with a gently sloping profile. They can vary in size, ranging from a few hundred meters to several kilometers in diameter. The height of lunar domes also varies but is generally much smaller compared to volcanic mountains found on Earth. Many lunar domes exhibit a high degree of symmetry, often appearing nearly circular. This symmetry is a result of the even distribution of lava as it erupted from the vent and spread outward.

EXAMPLE OF LUNAR DOMES

Several lunar domes have been identified and studied on the Moon’s surface. Some examples include:

MONS RÜMKER

Mons Rümker is a prominent lunar dome located in the western part of the Moon’s near side. It has a diameter of about 70 kilometers and a central pit crater. This dome is one of the most well-known lunar domes and has been studied extensively.

MONS PITON

Mons Piton is another lunar dome, located in the northeastern part of the Moon’s near side. It has a diameter of approximately 25 kilometers and a relatively flat summit.

MONS BRADLEY

Mons Bradley is a smaller lunar dome located near the eastern limb of the Moon. It has a diameter of about 5 kilometers and exhibits a well-preserved, symmetrical shape.

CINDER CONES

Cinder cones on the Moon, also known as lunar cinder cones or pyroclastic cones, are relatively small, conical-shaped volcanic structures that were formed by explosive eruptions of volcanic material, such as ash, dust, and cinders. While the Moon’s cinder cones are not as numerous or as prominent as those found on Earth, they provide important insights into the lunar volcanic history and the nature of volcanic activity on our celestial neighbour.

FORMATION

Lunar cinder cones formed through explosive volcanic eruptions that occurred during the Moon‘s history. These eruptions ejected volcanic fragments, including fine ash, dust, cinders, and small volcanic rocks, into the lunar vacuum. Unlike basaltic lava flows, which produced lunar maria, cinder cone eruptions resulted in the accumulation of these pyroclastic materials around the vent.

CHARACTERISTICS

Lunar cinder cones typically have a conical or mound-like shape with a central vent at the summit. They are generally smaller in size compared to cinder cones found on Earth. The pyroclastic materials ejected during the eruptions give them a lighter, often brighter appearance against the lunar surface.

SIZE

Lunar cinder cones can vary in size, with diameters ranging from a few hundred meters to several kilometers. They are relatively smaller and less massive than many terrestrial cinder cones.

COMPOSITION

The pyroclastic materials that make up lunar cinder cones are primarily composed of basaltic rocks, similar to the composition of lunar maria and the Moon’s crust in general. This basaltic material reflects sunlight differently from the surrounding lunar regolith, contributing to their distinct appearance.

DISTRIBUTION

Lunar cinder cones are scattered across various regions of the Moon, including both lunar maria and highland terrains. They are not concentrated in specific lunar mare regions but can be found in different locations.

AGE

The age of lunar cinder cones varies, but they are generally considered to be ancient geological features, dating back billions of years. Like other lunar volcanic features, they are remnants of the Moon’s more geologically active past.

VOLCANIC VENTS

Volcanic vents on the Moon are openings or fractures in the lunar surface through which volcanic material, such as lava, ash, and gases, once erupted during volcanic activity. These vents are crucial components of lunar volcanic features and provide valuable insights into the nature of volcanic activity on the Moon.

FORMATION

Lunar volcanic vents were formed as a result of volcanic activity during the Moon’s history. Volcanic eruptions occurred when molten rock (magma) from the Moon’s interior reached the surface through these openings, leading to the release of volcanic material.

CHARACTERISTICS

Lunar volcanic vents can vary in size and shape. They are often found at the summits of lunar volcanic features, such as cinder cones, pyroclastic deposits, and domes. The appearance of the vents depends on the specific volcanic feature and the type of eruption that occurred.

COMPOSITION

The volcanic material that erupted through lunar vents is primarily composed of basaltic rock, which is rich in iron and magnesium. This basaltic composition is consistent with the lunar crust and the materials found on the Moon’s surface.

TYPES OF ERUPTIONS

Lunar volcanic vents have been associated with various types of volcanic eruptions, including:

EFFUSIVE ERUPTIONS

Some vents were the sources of effusive eruptions, where relatively low-viscosity basaltic lava flowed from the vent and spread across the lunar surface. These eruptions contributed to the formation of lunar maria (volcanic plains).

EXPLOSIVE ERUPTIONS

Other vents were responsible for explosive eruptions that ejected pyroclastic material, such as ash and cinders, into the lunar vacuum. These materials accumulated around the vent and formed features like cinder cones and pyroclastic deposits.

DISTRIBUTION

Lunar volcanic vents can be found in various regions of the Moon, including both lunar maria and highland terrains. They are often associated with other volcanic features, such as lunar domes, rilles, and pyroclastic deposits.

AGE

The age of lunar volcanic vents varies, but they are generally considered to be ancient geological features, dating back billions of years. They are remnants of the Moon’s more active volcanic past.

DARK-HALO CRATERS

Dark-halo craters on the Moon are a type of lunar impact crater with distinctive dark or blackish deposits surrounding them. These dark-halo features have puzzled scientists for years, and their study has provided valuable insights into lunar geology and impact processes.

FORMATION

Dark-halo craters are formed through the impact of meteoroids or asteroids onto the lunar surface. When a celestial body collides with the Moon, it excavates material from beneath the lunar regolith (the loose layer of soil and rock on the surface). In the case of dark-halo craters, the impact exposes darker material from beneath the surface layers.

DARK-HALO DEPOSITS

The distinctive feature of dark-halo craters is the dark or blackish material that surrounds them. This material is known as the “dark-halo deposit” and is typically found in a relatively uniform ring or halo around the crater.

COMPOSITION

The dark-halo deposits are composed of a mixture of fine-grained, dark-coloured materials. They often contain various minerals, including pyroxenes and olivines, which contribute to their darker appearance. The specific composition may vary from one dark-halo crater to another.

ORIGIN OF DARK MATERIAL

The dark material in the halo is believed to be ancient volcanic material from the Moon’s interior. It is thought to have been exposed during the impact event and then settled around the crater, forming the distinctive halo.

EJECTA BLANKET

Dark-halo craters typically have an ejecta blanket composed of lighter-coloured material that was excavated during the impact. This lighter material contrasts sharply with the dark halo deposit, creating a visually striking feature.

DISTRIBUTION

Dark-halo craters are distributed across various regions of the Moon’s surface, both in lunar maria (volcanic plains) and highland terrains. They are not confined to specific lunar mare regions but can be found in different locations.

AGE

The age of dark-halo craters varies, as they can be found in different geological contexts on the Moon. Some are relatively young, while others are ancient, dating back billions of years. Their ages are determined based on their geological context and the superposition of other lunar features.