The Moon possesses a dramatically varied landscape featuring towering peaks and deep troughs, confirming that it has its own versions of mountains and valleys. These topographical features are fundamentally different from those on Earth because they were created and preserved by entirely different geological forces. While Earth’s topography is constantly reshaped by wind, water, and plate movements, the Moon’s surface is a static record of its violent ancient history.
The Lunar Highlands: Defining Lunar Mountains
The Moon’s elevated areas are most visible in the bright, heavily cratered regions known as the lunar highlands, or terrae. These mountains are not the result of tectonic plates colliding and uplifting crust, as is common on Earth. Instead, lunar mountains are primarily the rims of massive, ancient impact basins or the central peaks and ejecta blankets created by cosmic impacts. These impact-formed peaks can reach immense heights. For example, the Leibniz Beta mountain features an elevation change of up to 10 kilometers relative to the floor of a nearby crater.
Craters and Rilles: The Moon’s Valleys and Depressions
The most ubiquitous depressed features on the Moon are the countless impact craters, which serve as the primary form of lunar “valley” or depression. These bowl-shaped features are formed when objects from space collide with the surface, displacing material and leaving behind a circular hollow. The vast, dark, low-lying plains known as the Maria (Latin for “seas”) represent the largest depressed areas. These are enormous basins filled with dark, solidified basaltic lava flows that flooded the deepest impact structures billions of years ago. The Maria are generally much flatter and less cratered than the surrounding highlands.
Rilles
Linear depressions, often called rilles, also crisscross the surface, resembling deep channels or trenches. Sinuous rilles, such as the famous Hadley Rille, meander across the Maria and are interpreted as the remnants of collapsed lava tubes or surface lava channels. Straight rilles are flat-floored troughs, known as grabens, that formed when the crust pulled apart under tectonic stress. Arcuate rilles are curved trenches found near the edges of the Maria, likely formed when the heavy lava infill cooled and contracted, causing the basin floor to sag.
The Origin Story: How Lunar Topography Was Formed
The Moon’s current topography is a direct consequence of intense bombardment and subsequent internal activity in its first billion years. The earliest era saw the Moon battered by a huge number of large asteroids and comets, a period often referred to as the Late Heavy Bombardment. These impacts excavated the giant basins that would later become the Maria, while simultaneously creating the towering rims and uplifted ejecta fields that define the lunar mountains. Following this initial violent phase, internal heating led to a period of extensive volcanism. Magma flowed out through fractures in the crust, filling the lowest-lying impact basins and solidifying to form the flat, dark basaltic plains of the Maria. The lack of plate tectonics meant that this crustal reshaping stopped long ago, leaving the features permanently etched into the surface.