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Stratovolcano
A stratovolcano, also called a composite volcano, is a steep, conical volcano built from alternating lava flows, tephra, and pyroclastic flows, like Mount Fuji and Mount St. Helens.
Stratum
A stratum (plural strata) is a layer of rock distinguished from adjacent layers by lithologic properties. Their study, stratigraphy, traces how rock layers relate to geologic time.
Stratus cloud
Stratus cloud is a generally gray, low cloud layer with a fairly uniform base that may give drizzle, snow, or snow grains, sometimes forming from lifting fog.
Stream capture
Stream capture, also called river capture or stream piracy, is the natural diversion of a stream's water into a neighboring drainage basin, reorganizing river networks.
Stream gauge
A stream gauge is an installation on a river or stream that continuously records water-surface height, called stage, from which the flow volume, or discharge, is computed.
Stream metabolism
Stream metabolism is the combined rate of organic-carbon production and consumption in a stream, measured as gross primary production, ecosystem respiration, and net ecosystem production.
Stream power
Stream power is the rate at which a river expends energy, especially in transporting its sediment load, and underlies sediment transport theory, channel classification, and models of river incision.
Streamflow reconstruction
Streamflow reconstruction is a paleohydrology method that uses tree-ring chronologies, calibrated against gauge records, to estimate annual river flows back over a thousand years, helping water managers assess drought risk.
Streamwise vorticity
Streamwise vorticity is the component of vorticity parallel to the ambient wind. Tilted upward by storm updrafts, it creates the mesocyclone rotation that defines supercells.
Strike and dip
Strike and dip are the two measurements defining the orientation of planar geological features such as bedding planes and faults, and are fundamental to geologic mapping.
Strike-slip fault
A strike-slip fault is a fault where two sides slide past each other horizontally, occurring as transform plate boundaries or within continents, notably the San Andreas Fault.
Stromboli
Stromboli, northernmost of the Aeolian Islands in the Tyrrhenian Sea, is a persistently active stratovolcano whose regular mild explosions define the Strombolian eruption type; paroxysms in 1919, 1930, 2003, and 2019 mark its hazards.
Strong ground motion
Strong ground motion is the potentially damaging shaking of the ground or structures in an earthquake, recorded with accelerographs and analyzed for building codes and design.
Strontianite
Strontianite is a strontium carbonate mineral (SrCO3) of the aragonite group, named in 1791 after Strontian, Scotland, its type locality. Though the richer strontium ore, it is mined less than celestite.
Sturtian glaciation
The Sturtian glaciation was a global Snowball Earth glaciation of the Cryogenian Period, from about 717 to 660 million years ago, the longest in Earth history.
Subarctic climate
The subarctic climate, also called boreal climate, is a high-latitude continental climate with long, cold winters and one to three months averaging above 10 °C, underlying the boreal forest.
Subduction
Subduction is the process at a convergent plate boundary in which one tectonic plate, usually the denser oceanic plate, sinks beneath another into the mantle.
Submarine fan
A submarine fan is a large sediment accumulation on the ocean floor, built by turbidity currents; the Bengal Fan, the largest, is about 3000 km long.
Submarine groundwater discharge
Submarine groundwater discharge (SGD) is the flow of water from the seabed into the coastal ocean, combining fresh groundwater and seawater recirculated through coastal sediments.
Submarine landslide
A submarine landslide is the downslope movement of sediment or rock on the seafloor under gravity, occurring on slopes as gentle as 1 degree, destroying seabed infrastructure, and generating tsunamis.
Submersible
A submersible, or submersible craft, is a self-propelled underwater craft that carries personnel while operating below the surface and surfacing under its own buoyancy control.
Submesoscale ocean process
A submesoscale ocean process is an ocean current or circulation feature between mesoscale eddies and small-scale turbulence, with horizontal scales of roughly 1 to 10 km and time scales of hours to days.
Subsidence
Subsidence, also called land or ground subsidence, is the sinking of the Earth's surface caused by groundwater pumping, mining, or soil drainage; over 80 percent of known US subsidence stems from groundwater use.
Subsidence analysis
Subsidence analysis is a geology method that reconstructs a basin's downward movement through time, using backstripping to remove sediment loading and isolate tectonic subsidence, whose curve shape diagnoses basin type.
Subtropical climate
A subtropical climate is a climate zone between the tropics and temperate latitudes, typically found on eastern sides of continents between 20° and 35° latitude.
Subtropical gyre
A subtropical gyre is a large rotating system of ocean currents in each ocean basin, clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.
Subtropical jet stream
The subtropical jet stream is a band of strong westerly wind in the upper troposphere near 30° latitude, strongest in winter and driven by angular momentum conservation in the Hadley cell.
Subtropical mode water
Subtropical mode water (STMW) is a nearly uniform-temperature upper-ocean water mass, typically 250 m thick, formed by deep winter convective mixing on the equatorward side of western boundary current extensions in subtropical gyres.
Subtropics
The subtropics, or subtropical zone, are the climatic zones between the tropics and temperate regions, roughly 20 to 40 degrees of latitude in each hemisphere.
Suchitan
Suchitan (Suchitán) is a dormant twin-peaked andesitic stratovolcano, 2,042 m, in southeastern Guatemala northeast of Jutiapa, GVP 342160, with no confirmed historical eruptions; the 1469 report belongs to Atitlán.