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Water and gases bubbling up from beneath the Earth can mix with mud to create unique structures known as mud volcanoes. Unlike the famous igneous volcanoes that spew hot lava, mud volcanoes do not produce lava flows. Instead, pressure building deep underground pushes natural gases toward the surface. As these gases rise, they mix with sediment and mineral deposits. This mixture becomes a thick slurry that is pushed upward through cracks in the Earth called fissures or faults. When this slurry reaches the surface, it forms distinct structures. If these structures form while the Earth is covered by water, they are called submarine mud volcanoes. While mud volcanoes are not always caused by earthquakes or other seismic activity, they often appear near areas where the Earth's crust has cracked. These areas include subduction zones, where one tectonic plate moves under another, and lateral faults, where plates slide sideways past one another.
Mud volcanoes are generally much smaller than the standard igneous volcanoes that people often picture in their minds. The size of a mud volcano can vary significantly depending on the specific geological conditions. Some are small mounds that are only a few meters across, while others are massive structures that span several kilometers wide. Despite the wide range in dimensions, they all share the same fundamental formation process involving pressurized gas and mud moving from deep underground to the surface. This consistency in formation makes them a unique geological category despite their varied appearances.
Mud volcanoes can take on many different shapes depending on the specific conditions at the time of their formation. The shape is largely determined by the ratio of water to sediment, how active the volcano is, and the size of the underground channel that transports the mud. For instance, cone-shaped mud volcanoes usually form when the mud is thick and contains less water. This thicker mud moves slowly and builds up gradually around a central vent over a long period of time, creating a tall, pointed cone. In contrast, if the mud contains a high amount of water, it becomes much more fluid. This watery mud spreads out easily rather than piling up. As a result, it creates flatter, plateau-like structures. Scientists sometimes refer to these flat formations as mud pies because of their appearance.
Mud volcanoes and mud pots may look very similar to the untrained eye, but they form in very different ways. Mud pots are hot features often found in geothermal areas. In the United States, you can find mud pots in California at places like Lassen and the Salton Buttes. These areas are driven by intense heat from volcanoes underground. The mud pots bubble with a mixture of steam, gases, and highly acidic water. This hot, acidic water breaks down the surrounding rock into mud.
Mud volcanoes, often abbreviated as MVs, can pose serious risks to human structures located underwater. These include oil rigs, oil pipelines, communication cables, and wind farms. When mud volcanoes erupt, they often release large amounts of mud and methane gas into the ocean and the atmosphere. Research has estimated that mud volcanoes on land and in shallow water release between 2.2 and 6 million tons of methane into the atmosphere each year. Because of these potential risks and their significant impact on the environment, it is crucial for scientists to understand exactly where mud volcanoes are located around the world.
Mud volcanoes are cooler and form when pressurized mud and gas, most commonly methane and carbon dioxide, rise through faults to the Earth’s surface. Unlike mud pots, mud volcanoes do not always formed as a result of volcanic heat.
To address this need, researchers recently mapped 700 submarine mud volcanoes located in shallow seas. The resulting collection is known as the "Global Inventory of Submarine Mud Volcanoes." This inventory contains detailed information about where these mud volcanoes are located and what shapes they take. The new database includes both published data and new information calculated by the researchers. The published data includes specific details like location, height, diameter, water depth, and slope. The additional information calculated by the researchers includes estimated location, perimeter, area, volume, and various shape ratios.
This inventory of shallow sea mud volcanoes almost triples the number of known locations from previous records. It also adds new attribute information for every single feature found. The only previous global database of underwater mud volcanoes was published in 2015. That older database contained location information for only 258 features. In contrast, the 2025 study compiled size, shape, and slope data for 700 shallow sea mud volcanoes. This GIS data set is now available as a KMZ file for further study. This massive increase in data allows scientists to better understand the distribution and characteristics of these unique geological formations.
By understanding the location and behavior of mud volcanoes, researchers can better predict where they might erupt and how to protect human infrastructure. The detailed mapping of these 700 features provides a foundation for future research into methane emissions and underwater safety. The combination of precise location data and physical characteristics like volume and slope helps scientists model how these structures might impact the ocean floor and the atmosphere above. This work highlights the importance of continuous monitoring and data collection in geology. It shows how modern technology and systematic mapping can reveal the hidden dynamics of our planet's surface and subsurface. The transition from a database of 258 features to 700 represents a major leap forward in our ability to study these geological phenomena.
The study emphasizes that while mud volcanoes are often quiet and hidden underwater, they play a significant role in the Earth's natural systems. The release of methane is a key factor in climate studies, making these locations critical for environmental research. Furthermore, the potential threat to infrastructure means that accurate maps are essential for engineering projects in coastal and offshore areas. As technology improves, the ability to detect and map these features will only continue to grow. This ensures that future generations will have a more complete picture of the dynamic Earth beneath the waves.