Principles of Geology: Volcanism, Weathering, and Sedimentary Processes

Vocabulary flashcards covering volcanism patterns, tectonic controls, volcanic hazards and resources, mechanical and chemical weathering mechanisms, and sedimentary processes from the Principles of Geology lecture notes.

Spreading Centers

Divergent boundaries along mid-ocean ridges and continental rifts where decompression melting forms basaltic magma, representing the primary volcanic zone on Earth.

Subduction Zone Volcanism

The second most common volcanic setting, occurring where an oceanic plate subducts beneath continental or oceanic crust and triggers fluid-induced melting to generate andesitic or basaltic volcanic chains.

Fluid-Induced Melting

The melting mechanism operating at subduction zones where water and volatiles driven from the descending oceanic plate lower the melting temperature of mantle rock.

Intraplate Volcanism

Volcanic activity occurring within tectonic plates above mantle plumes, producing basaltic volcanism in oceanic domains (such as Hawaii) and rhyolitic volcanism in continental crust (such as Yellowstone).

Mantle Plume

A column of hot mantle material rising from deep within Earth that generates a surface hotspot, typically producing voluminous flood basalts from the plume head and an age-progressive volcanic trail from the plume tail.

Aseismic Ridge

A volcanic island or seamount track, such as the Hawaiian Island and Emperor Seamount chains, that displays an age progression of extinct volcanoes devoid of earthquake activity away from the active hotspot.

Columbia Plateau and Steens Basalt

Massive outpourings of fluid flood basalt that erupted beginning $17\,\text{million years}$ ago and traveled down the Columbia Gorge to the Willamette Valley and Pacific Ocean.

Snake River Plain Calderas

A series of massive volcanic calderas formed by explosive, viscous rhyolite magma across southern Idaho as the North American Plate drifted west-southwest over the Yellowstone hotspot.

Lahar

A dangerous volcanic mudflow or debris flow generated when hot pyroclastic material melts snow and ice or mixes with water, such as the $1985$ Andes disaster that killed $25{,}000$ people and traveled $50\,\text{km}$.

Jokulhlaup

A catastrophic glacial outburst flood triggered when subglacial volcanic activity or a lahar melts ice from underneath a glacier, rapidly releasing enormous volumes of water.

Pyroclastic Flow

A fast-moving, high-density current of superheated volcanic gases, ash, pumice, and lava blocks (especially silicon-rich) that rushes down a volcano's slopes, responsible for rapid burial of populations such as at Pompeii.

Tephra

All fragmental rock material ejected into the air by an explosive volcanic eruption, ranging in grain size from fine ash to large volcanic bombs, which poses severe respiratory hazards such as silicosis.

Volcanic Gases

Volatile substances released by magmas—principally $CO_2$, $SO_2$, $H_2S$, $HF$, $HCl$, and $HBr$—that contribute to atmospheric sulfur cycles and cause acid rain.

Flank Collapse

The structural failure of an unstable volcanic flank sliding into ocean waters, triggering megatsunamis exceeding $800\,\text{ft}$ in height capable of transporting semi-truck-sized boulders across $30\,\text{miles}$ of ocean.

Caldera Collapse

The structural collapse of a volcanic edifice following the rapid evacuation of its underlying magma reservoir, exemplified by Long Valley Caldera (venting $CO_2$ since $1992$) and Yellowstone (uplifting at $7\,\text{cm/year}$ since $2004$).

Andisols

Highly fertile soil orders formed from the weathering of volcanic ash, pumice, and other volcanic parent materials.

Hydrothermal Vents

Mineral-rich vents on ocean spreading centers where volcanically heated seawater leaches, concentrates, and deposits metals and chemical elements into the ocean.

Geothermal Energy

Renewable electrical generation system where cold water is injected into hot subsurface rocks near magma, generating steam that rises to drive electrical turbines.

Sedimentary Stages of the Rock Cycle

The geological sequence starting with weathering and erosion of rock at an outcrop, downhill transportation, particle deposition, accumulating burial, and eventual diagenetic lithification.

Pressure-Release Jointing (Unloading)

A mechanical weathering process occurring when erosion strips away overlying rock or glacial ice, relieving confining pressure and allowing underlying rock to expand and fracture.

Sheeting

The physical weathering process where rock fractures and peels away in concentric layers or sheets parallel to the outcrop surface as a result of unloading expansion.

Exfoliation Dome

A massive, rounded rock landform, such as Half Dome in Yosemite in the Sierra Nevada Mountains, created by large-scale sheeting over exposed plutonic rock bodies.

Salt Wedging

A mechanical weathering mechanism common in coastal and semi-arid environments where salt crystals grow and expand within rock pores and fractures, prying apart mineral grains.

Tafoni

Distinctive honeycomb-like weathering pits and cavernous cavities formed in rock exposures, particularly seen along coastal areas like Salt Point on the Sonoma Coast, as a result of salt wedging.

Chemical Weathering

The alteration, breakdown, and dissolution of minerals into water-soluble ions via chemical reactions (carbonic acid dissolution, hydrolysis, and oxidation), which accelerates with higher temperature, moisture, and surface area.

Calcite Dissolution

The chemical breakdown of calcite by natural carbonic acid according to the reaction: $CaCO_3 + H_2CO_3 \rightleftharpoons 2HCO_3^- + Ca^{2+}$.

Hydrolysis

A chemical weathering reaction in which silicate minerals react with water, demonstrated by the decomposition of potassium feldspar into kaolinite clay and quartz: $2KAlSi_3O_8 + 3H_2O \rightarrow Al_2Si_2O_5(OH)_4 + 4SiO_2 + 2K^+ + 2OH^-$.

Goldrich Stability Series

A relative weathering vulnerability series showing that minerals crystallizing first at high temperatures (olivine and Ca-rich plagioclase) weather fastest, whereas minerals crystallizing last (quartz) weather slowest.