A fissure is a narrow crack, split, or groove in a solid surface or structure. The word comes from the Latin fissura, meaning “a cleft,” and it appears across wildly different fields, from geology and medicine to dentistry and structural engineering. What ties all the uses together is the core image: a material that was continuous has separated along a line. Beyond that shared idea, though, the causes, consequences, and treatments of fissures diverge sharply depending on whether you are talking about a crack in the Earth’s crust, a painful tear in skin, or a groove on the surface of your brain.
Geological Fissures
In geology, a fissure is a fracture in the Earth’s crust that can range from a hairline crack in surface rock to a gaping rift kilometers long. The most dramatic examples are volcanic fissures, where magma rises through elongated fractures rather than erupting from a single central vent. In Iceland, for instance, entire fissure swarms run along the mid-Atlantic rift zone. The linear arrays of volcanic vents that mark these fissures are bounded by vertical faults, and the surrounding rock tilts inward as the ground subsides during eruptions. Researchers have proposed that the fissures have vertical feeder channels with lateral branches extending along the rift, and the inflation and deflation of these channels during eruptive cycles drives the subsidence and faulting seen at the surface.1Tectonics. Magmatic fissures and their systems in Iceland: A tectonomagmatic model
Fissure-fed volcanism is not unique to Iceland. In the Ethiopian Rift, extension fractures in the Earth’s crust serve as direct channels for magma to reach the surface, and most elongated volcanic vents and linear volcanic clusters in the region sit atop these fractures.2Journal of Volcanology and Geothermal Research. Volcanic vents rooted on extension fractures and their geodynamic implications in the Ethiopian Rift In the Andes, a transtensional tectonic setting drives parallel dyking and fissural eruptions that progressively shape the elongated anatomy of certain volcanoes over tens of thousands of years. The same process that builds the volcano also steepens its flanks, which can make it more prone to sector collapse.3Quaternary International. Transtension driving volcano-edifice anatomy: Insights from Andean transverse-to-the-orogen tectonic domains
Not all geological fissures involve volcanoes. In arid and semi-arid regions, pumping groundwater from deep aquifers can cause the land above to settle unevenly, cracking the surface. These “earth fissures” are a serious hazard in places where the ground profile includes a stiff cemented layer on top of a thick aquifer. The rigid cap does not flex gracefully as the water table drops; instead, stress concentrates and the surface fractures. Finite-element modeling has shown that the properties of that cemented layer, its thickness and stiffness, are key factors controlling where and how earth fissures form.4Quarterly Journal of Engineering Geology and Hydrogeology. Earth fissure formation from groundwater pumping and the influence of a stiff upper cemented layer This type of ground cracking damages roads, pipelines, and foundations in parts of the American Southwest, northern China, and the Middle East.
Fissures in Human Anatomy
In anatomy, the word “fissure” describes grooves, clefts, or dividing lines in organs and bones that are entirely normal. These are not injuries; they are features of how the body is built.
The brain is a good example. The folds on the brain’s surface create ridges and valleys. The ridges are called gyri and the valleys are called sulci, and these are the standard anatomical terms used to map different regions of the cortex.5PubMed Central. Fundamental functional differences between gyri and sulci: implications for brain function, cognition, and behavior Especially deep sulci are traditionally called fissures. The longitudinal fissure runs front to back between the two hemispheres. The lateral fissure (sometimes called the Sylvian fissure) separates the temporal lobe from the frontal and parietal lobes. These are landmarks that neurosurgeons and neurologists rely on to orient themselves within the brain.
The lungs also have fissures. These are formed by a double-layered fold of the membrane that covers the lungs, and they divide each lung into its lobes. The right lung has two fissures (an oblique and a horizontal one), creating three lobes. The left lung has one oblique fissure, creating two lobes.6Cureus. Anatomical Variations in Pulmonary Fissures on Computed Tomography (CT) On chest X-rays, the major lung fissures normally appear as hairline-thin lines; on high-resolution CT scans, they show up as sharp lines separating the lobes.7PubMed. Radiographic and CT appearances of the major fissures These fissures matter clinically because fluid can collect along them, infections can be contained within a single lobe, and surgeons sometimes need to operate along fissure planes.
Pulmonary fissure anatomy varies quite a bit from person to person. Some people have incomplete fissures, where the lobes are partially fused. Others have accessory fissures that create extra subdivisions. These variations are usually harmless, but they can change surgical planning and affect how diseases like pneumonia spread within the lung.
The Superior Orbital Fissure
One anatomical fissure that comes up in emergency medicine is the superior orbital fissure, a gap between bones at the back of the eye socket. Several important nerves and blood vessels pass through this narrow opening, including the nerves that control eye movement and sensation in the forehead and upper eyelid. If a facial fracture compresses the structures passing through this fissure, the result is superior orbital fissure syndrome, a constellation of problems including paralysis of eye movement, a drooping eyelid, a fixed dilated pupil, and numbness in the upper face. This complication occurs in fewer than one in a hundred cases of craniofacial trauma.8PubMed Central. Traumatic superior orbital fissure syndrome: current management Treatment is usually conservative, meaning doctors watch and wait for the nerve compression to resolve on its own, unless bone fragments are directly impinging on the nerves or the optic nerve itself is at risk.9PubMed Central. Traumatic superior orbital fissure syndrome: Review of literature and report of three cases
Anal Fissures
When most people hear “fissure” in a medical context, they are probably thinking of an anal fissure, a small tear in the lining of the anal canal. It is one of the most common causes of sharp pain during bowel movements and often causes bright red bleeding on toilet paper. Most acute anal fissures heal on their own within a few weeks with simple measures like fiber supplements, plenty of water, and warm baths.
The ones that do not heal tend to become chronic, and that is where the physiology gets interesting. The current understanding is that an initial tear triggers pain, which causes the internal anal sphincter to tighten. That increased resting pressure reduces blood flow to the tissue around the tear, which creates a low-oxygen environment that prevents healing, which keeps the tear open, which keeps triggering pain, and the cycle repeats.10PubMed. Increased anal basal pressure in chronic anal fissures may be caused by overreaction of the anal-external sphincter continence reflex Breaking that cycle is the goal of every treatment: reduce the sphincter pressure, restore blood flow, and let the tissue heal.11PubMed Central. Anal fissure
First-line treatments for chronic anal fissures include topical medications like nitroglycerin ointment or calcium channel blockers, which relax the sphincter muscle chemically. Oral L-arginine, a supplement that serves as a building block for nitric oxide in the body, has also shown promise in relaxing the internal sphincter and improving healing in clinical trials.12PubMed Central. L-Arginine is a feasible supplement to heal chronic anal fissure via reducing internal anal sphincter pressure: a randomized clinical trial study When topical treatments fail, botulinum toxin injections into the sphincter are another option. The injection temporarily paralyzes part of the muscle, lowering the pressure and allowing healing. Surgical internal sphincterotomy, where a surgeon makes a small cut in the sphincter to permanently reduce its tone, has a higher healing rate and lower recurrence than botulinum toxin injections, but it carries a greater risk of affecting continence afterward.13PubMed. Botulinum toxin injection versus lateral internal sphincterotomy in the treatment of chronic anal fissure: a randomized controlled trial That tradeoff often means doctors try the less invasive approaches first and reserve surgery for fissures that keep coming back.14PubMed Central. Minimal Lateral Internal Sphincterotomy (LIS): Is It Enough to Cut Less Than the Conventional Tailored LIS?
Skin Fissures
The term “fissure” also describes cracks in the skin, particularly on the hands and feet. Skin fissures tend to develop in areas where the skin is thick and dry: heels, fingertips, and the spaces between toes. When the outermost layer of skin loses too much moisture and becomes rigid, normal movement causes it to split rather than flex. The cracks can be shallow and painless, or deep enough to reach living tissue underneath, where they bleed and sting.
Cold dry weather, frequent hand washing, contact with irritating chemicals, and conditions like eczema or psoriasis all increase the risk. On the feet, heel fissures are especially common in people who walk barefoot or wear open-backed shoes. Treatment centers on restoring moisture and softening the hardened skin. Formulations containing humectants like urea and alpha-hydroxy acids are commonly used for dry, cracked feet with fissures and thickened skin.15PubMed Central. The influence of a humectant-rich mixture on normal skin barrier function and on once- and twice-daily treatment of foot xerosis For deeper cracks, liquid bandages or medical-grade skin adhesives can hold the edges together while new skin grows underneath.
Dental Fissures and Sealants
In dentistry, “fissures” refers to the narrow grooves and pits on the chewing surfaces of your molars and premolars. These are normal anatomy, not damage. But they are among the most cavity-prone spots in the mouth because toothbrush bristles are often too wide to clean out the bottoms of these grooves, allowing bacteria and food debris to accumulate.
Pit and fissure sealants were introduced in the 1960s specifically to address this vulnerability. A sealant is a thin resin coating painted into the grooves, where it hardens and creates a smooth, sealed surface that bacteria cannot colonize. Evidence from systematic reviews confirms that fissure sealants are effective at preventing cavities in children and adolescents compared to leaving teeth unsealed.16Cochrane Database of Systematic Reviews. Pit and fissure sealants for preventing dental decay in permanent teeth Sealants are most often applied to the permanent molars shortly after they erupt, typically between ages six and twelve. They are quick to place, painless, and generally last several years before they may need to be reapplied.
Fissures in Concrete and Building Materials
Engineers use “fissure” and “crack” somewhat interchangeably, though “fissure” sometimes implies a smaller or earlier-stage fracture. In concrete, the progression from micro-fissure to macro-crack is a well-studied failure pathway. Concrete is strong in compression but weak in tension, and when tensile forces exceed the material’s limit, tiny microcracks form first, especially at the boundaries between the cement paste and the aggregate (the gravel and sand mixed into concrete). Under continued loading, these microcracks grow and link up. When scattered microcracks coalesce into a continuous through-going fracture, the structure’s ability to carry loads drops sharply.17PubMed Central. Numerical Simulation of Crack Propagation in Concrete with Prefabricated Array Fractures Based on the Discrete Element Method Interestingly, evenly scattered microcracks can coexist with relatively high residual strength; it is the concentrated merging into a single dominant crack that causes failure.
Researchers study this process at the mesoscopic scale, looking at how cracks interact with individual aggregate particles inside the concrete. Cracks tend to propagate along the weaker interfaces between cement mortar and aggregate until they encounter a particularly hard piece of aggregate, at which point they either detour around it or, under high enough stress, cut straight through.18Scientific Reports. Study on the mesoscopic failure and fractal characteristics of concrete with holes and cracks Understanding these pathways helps engineers design concrete mixes and reinforcement strategies that delay the transition from harmless micro-fissures to dangerous macro-cracks.
Outside of concrete, desiccation fissures are a concern in clay soils. When clay dries out, it shrinks as moisture leaves the spaces between particles. If the shrinkage is uneven, tensile stress builds up and the surface cracks into the polygonal patterns you see in dried mud flats. The extent and depth of cracking depend on the balance between capillary pressure pulling particles together and the tensile strength of the soil resisting fracture.19Geotechnical and Geological Engineering. Modeling and Mechanisms of Desiccation-Induced Cracking and Curling in Clay Soils: A State-of-the-Art Review These cracks are a practical problem in earthen dams, clay liners under landfills, and foundations on expansive soil.
Self-Healing Concrete
One of the more inventive responses to cracking in concrete is bio-self-healing concrete. The concept involves embedding dormant bacteria within the concrete mix during construction. The bacteria remain inactive as long as the concrete is intact. When a crack forms and moisture seeps in, the bacteria wake up, consume nutrients placed alongside them, and produce calcium carbonate, the same mineral found in limestone. This calcium carbonate fills the crack and restores some of the material’s structural integrity.20PubMed Central. Bacteria-powered self-healing concrete: Breakthroughs, challenges, and future prospects
The biological approach is one of several strategies for autonomous crack repair. Chemical methods use embedded fibers, crystalline admixtures, or polymer capsules that release healing agents when a crack ruptures them.21Journal of Materials Research and Technology. Microbial self-healing in concrete: A comprehensive exploration of bacterial viability, implementation techniques, and mechanical properties Both biological and chemical self-healing approaches are most effective for micro-fissures; once a crack widens past a certain point, autonomous repair cannot keep up, and traditional patching or structural reinforcement is needed. Still, the ability to seal tiny cracks before water and corrosive chemicals penetrate to the steel reinforcement inside could dramatically extend the lifespan of bridges, tunnels, and marine structures.
Detecting Hidden Fissures
Finding fissures before they cause problems is a challenge in both medicine and engineering. In the lungs, as mentioned above, CT imaging is the standard tool: high-resolution scans can distinguish normal fissure anatomy from abnormal fluid collections or incomplete fissures that might affect surgical planning.22PubMed. Radiographic and CT appearances of the major fissures
For geological and mining-related fissures, the problem is trickier because the cracks may be underground and invisible from the surface. In coal mining areas, ground fissures caused by underground extraction can remain hidden until they suddenly swallow equipment or disrupt water tables. A combined detection approach using drone-mounted infrared cameras and ground-penetrating radar has shown promise. The infrared technique exploits the fact that the ground surface directly above a hidden fissure tends to be warmer than the surrounding area, because the crack changes how heat moves through the soil. Ground-penetrating radar then provides a subsurface profile to confirm the fissure’s location and depth.23International Journal of Rock Mechanics and Mining Sciences. Detection of hidden mining-induced ground fissures via unmanned aerial vehicle infrared system and ground-penetrating radar Used together, the two methods can map hidden fissures efficiently enough to guide where mining or construction activity should be restricted.
Fissures Beyond Earth
Perhaps the most unexpected use of the word “fissure” in recent science involves Saturn’s moon Enceladus. The Cassini spacecraft discovered in 2005 that four long, roughly parallel fractures near Enceladus’s south pole, nicknamed “tiger stripes,” were actively spraying plumes of water ice and vapor into space. These are fissures in the moon’s ice shell, and they have been erupting more or less continuously since their discovery, though the intensity fluctuates with tidal forces as Enceladus orbits Saturn.
Modeling suggests that the tiger stripes behave as tidally flexed slots that puncture the entire ice shell. As Enceladus moves through its elliptical orbit, Saturn’s gravity stretches and compresses the moon slightly, opening and closing these fissures in a rhythmic cycle. Frictional heating within the fissure walls as they flex may generate enough energy to explain both the sustained eruptions and the total heat output of the tiger stripe region. The model implies that once these fissures form, tidal energy can maintain them over geological timescales, potentially keeping a subsurface ocean in contact with the vacuum of space for millions of years.24PubMed Central. Sustained eruptions on Enceladus explained by turbulent dissipation in tiger stripes That long-lived connection between a liquid water ocean and the surface is one of the reasons Enceladus is considered a top candidate in the search for extraterrestrial life. The fissures, in a sense, are windows into a hidden ocean, and future missions may fly through the plumes to sample what comes out of them.