5,021 articles
Magma chamber
A magma chamber, also called a magmatic reservoir, is the region beneath a volcano's vent where molten rock (magma) is stored prior to eruption, often as crystal-rich mush.
Magnesian Limestone
Magnesian Limestone is a Permian succession of dolomites deposited about 255 million years ago on the margins of the Zechstein Sea, outcropping from Nottinghamshire to County Durham.
Magnesite
Magnesite is a magnesium carbonate mineral, MgCO₃, in the calcite group, mined as the principal ore of magnesium and heated to MgO, a refractory that lines steelmaking furnaces.
Magnetic anomaly detection
Magnetic anomaly detection (MAD) analyzes measured local magnetic fields to detect weak magnetic sources such as buried ferromagnetic material, applied in mineral exploration, unexploded ordnance clearance, archaeology, and military submarine detection.
Magnetic declination
Magnetic declination, also called magnetic variation, is the angle between magnetic north, where a compass points, and true north; it changes with location and time, and compass bearings must be corrected by it.
Magnetic survey
A magnetic survey is a geophysical method that maps spatial variations in Earth's magnetic field to image subsurface geology, mineral deposits, and buried structures, measured in nanotesla.
Magnetostratigraphy
Magnetostratigraphy is a stratigraphic technique that dates and correlates rocks by matching their record of magnetic polarity reversals against the geomagnetic polarity time scale, providing time lines where direct dating is not possible.
Magnetotellurics
Magnetotellurics is a passive geophysical method that uses natural electric and magnetic field variations to image subsurface electrical conductivity from hundreds of meters to hundreds of kilometers deep.
Magnitude of completeness
The magnitude of completeness (Mc) is the lowest magnitude at which 100% of earthquakes in a region are reliably detected by a seismic network; below it, smaller quakes are missed.
Maharashtra floods of 2005
The Maharashtra floods of 2005, also called the Mumbai Mega Flood, killed about 1,094 people after Mumbai recorded 944.2 mm of rain in 24 hours on 26 July.
Main Central Thrust
The Main Central Thrust (MCT) is a major thrust fault running nearly the entire length of the Himalaya, first named by Heim and Gansser in 1939.
Majorite
Majorite is a high-pressure garnet-group mineral in which silicon enters octahedral sites, occurring in the mantle transition zone and in shocked meteorites; it was named for Alan Major.
Makrana marble
Makrana marble is a white calcite marble quarried at Makrana in Rajasthan, India, the stone of the Taj Mahal and Asia's first Global Heritage Stone Resource in 2023.
Malachite
Malachite, also known as Bremen green as a pigment, is a green copper carbonate mineral used for thousands of years as a copper ore, pigment, gemstone, and sculptural material.
Malmberget mine
The Malmberget mine is a large underground iron ore mine at Malmberget near Gällivare in Swedish Lapland, operated by the state-owned company LKAB since 1890.
Mammatus cloud
Mammatus cloud, also written mamma, is a supplementary cloud feature of rounded pouches hanging from a cloud base, often on thunderstorm anvils, and is not a tornado signal.
Manam
Manam (Manam Motu) is a basaltic-andesitic stratovolcano island, 10 km wide, 13 km off Papua New Guinea's Madang coast; eruptions recorded since 1616, two summit craters, major 2004-05 and 2019 eruptions, and top-tier global volcanic SO2 and CO2 emissions.
Mancos Shale
The Mancos Shale is a Late Cretaceous marine shale formation of the Western Interior of the United States, named in 1899 for Mancos Valley and the town of Mancos, Colorado.
Manganese nodule
A manganese nodule, also called a polymetallic nodule, is a potato-sized concretion of iron and manganese oxides lying loose on the deep seabed, rich in nickel, copper, and cobalt.
Mantle (geology)
The mantle is the mostly solid silicate layer of Earth between the crust and core, about 2,900 km thick, whose slow flow drives plate tectonics and volcanism.
Mantle convection
Mantle convection is the slow creeping flow of Earth's solid mantle, which moves a few centimeters per year and drives the plate tectonics responsible for earthquakes, mountain ranges, and volcanoes.
Mantle plume
A mantle plume is a buoyant upwelling of hot, low-viscosity rock rising through Earth's mantle, proposed in the 1970s to explain hotspot volcanism; the classic example is the Hawaiian chain.
Mantle transition zone
The mantle transition zone (MTZ) is the layer of Earth's mantle between about 410 and 660 km depth, separating the upper mantle from the lower mantle.
Map
A map is a symbolized representation of geographic reality showing selected features for situations where spatial relationships matter most; making and studying maps is called cartography.
Marble
Marble is a metamorphic rock formed when limestone or dolostone recrystallizes under heat and pressure, prized for sculpture and architecture since antiquity for its polish and workability.
Marcellus Formation
The Marcellus Formation, also called the Marcellus Shale, is a Middle Devonian black shale in the Appalachian basin, extensively developed for natural gas since 2007.
March 2026 North American blizzard
The March 2026 North American blizzard was a major winter storm from March 14 to 16, 2026, dumping 30.9 inches on Wausau, Wisconsin, its largest snowstorm on record.
Marginal ice zone
The marginal ice zone (MIZ) is the dynamic interface between open ocean and sea ice, where waves break the cover into small floes and strongly influence atmosphere–ocean heat fluxes.
Mariana Trench
The Mariana Trench is the deepest oceanic trench on Earth, in the western Pacific Ocean east of the Philippines near Guam, whose deepest point, Challenger Deep, reaches about 10,935 meters.
Maricunga belt
The Maricunga belt is a metallogenic belt in the Andes of northern Chile hosting epithermal and porphyry gold deposits, with about 40 million ounces of gold discovered since 1980.