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Primitive equations
The primitive equations are the set of atmospheric and oceanic motion equations, simplified by the hydrostatic approximation, used in most numerical weather prediction and climate models.
Principle of faunal succession
The principle of faunal succession is the geologic principle that fossils appear in a definite, recognizable order, so rock layers can be matched and relatively dated by their fossils.
Principles of Geology
Principles of Geology is a three-volume work by Scottish geologist Charles Lyell, published between 1830 and 1833, arguing that present-day processes shaped Earth's past and heavily influencing Darwin.
Probabilistic seismic hazard analysis
Probabilistic seismic hazard analysis (PSHA) is a method that estimates the annual frequency of earthquake ground shaking exceeding specified levels at a site, formalized by C. Allin Cornell in 1968.
Probable maximum flood
The probable maximum flood (PMF) is the flood resulting from the most severe meteorological and hydrologic conditions reasonably possible for a drainage basin, used as the upper-limit design flood for high-hazard dams.
Probable maximum precipitation
Probable maximum precipitation (PMP) is the greatest rainfall depth meteorologically possible at a location, the design basis for extreme floods at dams and nuclear plants.
Prograde metamorphism
Prograde metamorphism is the recrystallization of a rock toward higher metamorphic grade as pressure, temperature, and fluid pressure rise; its gradual form is called progressive metamorphism.
Project Azorian
Project Azorian, also known as Project Jennifer, was a secret CIA operation during the Cold War to raise the sunken Soviet submarine K-129, lost with all hands in 1968.
Project Mogul
Project Mogul, also called Operation Mogul, was a top secret US Army Air Forces program from 1947 to 1949 that used high-altitude balloons to detect Soviet atomic tests.
Project Mohole
Project Mohole (1957–1966) was an American scientific program led by the American Miscellaneous Society that attempted to drill through the oceanic crust to the Mohorovičić discontinuity.
Project Stormfury
Project Stormfury was a joint US Navy and NOAA program, running from 1962 to 1983, that tried to weaken hurricanes by seeding them with silver iodide.
Prosperite
Prosperite is a rare hydrated calcium zinc arsenate mineral, approved in 1978 and known only from the second oxidation zone of the Tsumeb Mine in Namibia, where it forms white prismatic crystals up to 10 mm.
Proterozoic
The Proterozoic, or Proterozoic Eon, is the second of Earth's four geological eons, spanning 2,500 to 541 million years ago and forming most of the Precambrian.
Protolith
A protolith, also known as the parent rock or precursor, is the original unmetamorphosed rock that a metamorphic rock formed from; it may be igneous, sedimentary, or previously metamorphosed.
PSJ Cobre Mendocino
PSJ Cobre Mendocino, formerly the San Jorge project, is a copper-gold porphyry mining project in Uspallata, Mendoza Province, Argentina, developed by Minera San Jorge S.A.
Public opinion on climate change
Public opinion on climate change, the measured beliefs, risk perceptions, and policy preferences gathered through repeated surveys, shows large majorities worldwide accept climate change and want stronger government action.
Pull-apart basin
A pull-apart basin is a structural depression formed by localized crustal extension at a releasing bend or stepover in a strike-slip fault system, named in 1966, with the Dead Sea basin among the largest.
Pululahua
Pululahua, a potentially active dacitic-andesitic lava dome complex 15 km north of Quito, Ecuador, with a ~3 km depression formed by VEI ~4 eruptions 2.6–2.3 ka; last eruption ~2.2 ka; inhabited crater and geobotanical reserve.
Pumice
Pumice is a light-colored, highly vesicular volcanic rock, a froth of silicic glass that forms in explosive eruptions; its sealed pores make most varieties float on water.
Pump-and-treat
Pump-and-treat (P&T) is a groundwater remediation method that pumps contaminated water from wells to an above-ground treatment system; it has been used at over 800 US Superfund sites.
Pumping test
A pumping test pumps a well at a regulated rate while measuring water levels in observation wells to estimate aquifer properties such as transmissivity and storativity.
Purico Complex
Purico Complex, a Pleistocene pyroclastic shield volcano in northern Chile's Central Volcanic Zone at 23°S 67.75°W, 5,703 m high, formed by two ~1.3 Ma ignimbrite sheets with Holocene domes, the Macon stratovolcano, and the active Alitar maar.
Putana
Putana (Jorgencal, Machuca) is a 5,884 m Holocene stratovolcano on the Chile-Bolivia border in the Central Andean arc, with vigorous summit fumaroles, sulfur mining, a reported 1810 CE eruption, and 2009 uplift unrest.
Pycnocline
A pycnocline is the ocean layer where water density changes most rapidly with depth, typically caused by temperature or salinity gradients, which restricts vertical mixing and stabilizes the water column.
Pyramidal peak
A pyramidal peak, also called a glacial horn, is a sharp pyramid-shaped summit formed when cirque glaciers erode a mountain from three or more sides; the Matterhorn is the type example.
Pyrite
Pyrite, also called iron pyrite, is a common iron disulfide mineral (FeS₂) with a brass-yellow metallic luster nicknamed fool's gold; its oxidation causes acid mine drainage.
Pyrochlore
Pyrochlore is a brown to black niobium oxide mineral with a cubic crystal structure, first described in Norway in 1826, and the world's primary source of niobium.
Pyroclastic flow
A pyroclastic flow, also called a nuée ardente, is a hot, dense mixture of volcanic ash, rock fragments, and gas that races down a volcano's flanks at over 100 km/h.
Pyrocumulonimbus
A pyrocumulonimbus, or pyroCb, is a thunderstorm generated by wildfire heat, officially named flammagenitus, that injects smoke high into the atmosphere and spreads embers and lightning.
Pyrolusite
Pyrolusite is a manganese oxide mineral with formula MnO₂, the most stable polymorph of manganese dioxide and the principal ore of manganese, used to decolorize glass since antiquity.