The surface of the Earth presents a dramatic range of elevations, from soaring mountain peaks to the ocean floor’s abyssal plains. The planet’s lowest points, situated beneath the surface of the global sea, offer a fascinating study in geology and human endeavor. These unique depressions exist through two primary mechanisms: immense natural forces that shape the Earth’s crust and large-scale engineering projects designed to reclaim land from water. Understanding these places requires a precise definition of the reference point used for all elevation measurements.
Understanding the Zero Point
All geographic heights and depths are measured against a standardized baseline known as Mean Sea Level (MSL). This zero point is not a fixed, physical line but rather an average height of the ocean’s surface over a long period, accounting for the constant fluctuations caused by tides and currents. For scientists, this average is aligned with a mathematical model of Earth’s gravity field called the geoid, which represents the theoretical surface of the ocean if it were only affected by gravity and rotation.
Land elevation refers to the vertical distance above MSL, while bathymetry describes the depth of the ocean floor below the water surface. Measuring land that sits below MSL is a direct application of this system, designating the negative distance from the average ocean height to the dry ground. This reference point is fundamental to cartography and engineering, establishing a stable standard for quantifying Earth’s topography.
Naturally Occurring Below-Sea-Level Locations
Naturally formed depressions on land are found in hot, arid regions where evaporation rates far exceed water inflow, preventing the basins from filling completely. The lowest exposed land on Earth is the shoreline of the Dead Sea, which sits at approximately 431 meters (1,410 feet) below sea level. This hypersaline lake occupies the Jordan Rift Valley, a geological feature formed by the slow separation of the African and Arabian tectonic plates. This plate movement causes the intervening crustal block to drop, a process called subsidence, creating the deep, fault-bounded basin.
The lowest point in Africa is the shore of Lake Assal in Djibouti, which lies 155 meters (509 feet) below MSL. This highly saline crater lake is located in the Afar Depression, another rift zone where tectonic plates are pulling apart. Heat and evaporation in this scorching desert climate concentrate the water’s salt content, making it one of the world’s saltiest bodies of water.
In North America, the lowest elevation is found in Death Valley’s Badwater Basin, California, reaching 86 meters (282 feet) below sea level. This basin is formed by the extensional tectonics of the Basin and Range Province. The Earth’s crust is stretched and fractured, causing large blocks of land to slide downward along faults, creating alternating mountain ranges and sinking valleys. These natural depressions are sealed basins where water collects but has no outlet to the sea, leaving behind vast salt flats as the water evaporates.
Regions Maintained by Human Engineering
In contrast to these geological formations, some significant below-sea-level areas exist only through continuous human intervention. The Netherlands is the most famous example, where approximately a quarter of the land surface is below MSL and requires constant management. Large tracts of land, known as polders, were reclaimed from the sea or lakes and are protected by an elaborate system of dikes.
The Flevoland polders, including the world’s largest artificial island, were created from the former Zuiderzee and lie up to 6.20 meters below the local reference datum. Maintaining these areas involves an intricate network of canals which collect excess water. Massive electric and diesel pumping stations continuously discharge this water into surrounding, higher-lying water bodies, operating with a combined capacity that moves thousands of cubic meters of water per minute.
Another major urban area relying on engineered defenses is New Orleans, Louisiana. A significant portion of the city is below MSL due to a combination of natural subsidence and the compaction of reclaimed marshland. The city is encircled by a system of levees and floodwalls designed to keep water out. Since the city sits in a bowl-like basin, all rainwater must be actively pumped out. This is achieved by a vast network of drainage canals and over two dozen pumping stations with a combined capacity exceeding 45,000 cubic feet of water per second, preventing the city from flooding during heavy rainfall events.