VOLCANISM, FOLDS, AND FAULTS LECTURE NOTES
VOCABULARY: diastrophism, isostacy, volcanism, plutonism, lava, magma, intrusive, extrusive, batholith, stock, laccolith, dike, volcanic neck, lava flow, fissure, volcano, vent, shield cone, cinder cone, composite cone, pyroclastic debris, quiet, explosive, volatiles, crater, caldera, intermediate, fissure, gasses and vapors, volcanic bombs, blocks, cinders, ash, dust, aa, pahoehoe, pillow, mud torrent, earthquake, seismology, seismograph, focus, Mercalli scale, Richter scale, epicenter, fold, fault, law of original horizontality, cross-bedding, law of superposition, law of cross cutting relations, relative dating, unconformity, contact, geologic map, block diagram, cross section, anticline, syncline, dome, basin, recumbent fold, dip, strike, differential erosion, joint, fault, vertical fault, normal fault, reverse fault, hanging wall, foot wall, hanging wall block, footwall block, overthrust fault, horizontal fault, strike-slip fault, transform fault, fault plane, fault trace, fault scarp, horst, graben, thrust fault, fault-block mountain
diastrophism--folding, warping, and faulting (breaking of the crust)
isostacy--balancing of crust
volcanism--all process which give rise to magma, cause it to move, its expulsion from the earth, and which may refer to near or at surface only
plutonism--refers only to magmatic actions
magma moves toward the surface by: cracking and breaking rocks; melting overlying
•magma--molten rock within the earth
•lava--molten rock at or near the earth's surface
•intrusive--magma and resultant igneous bodies within the earth
•extrusive--lava and resultant igneous bodies at or near the earth's surface
types of intrusive bodies--(molten or solid)
- batholith--large pocket of magma or rock cooled from magma
- stock--small pocket of magma or rock cooled from magma (a small batholith)
- laccolith--a "blister" which causes overlying layers to dome or bend upward
- dike--magma cutting through preexisting rocks which is vertical or somewhat vertical; a discordant intrusion
- sill--magma penetrates between two rock layers forming a flat sheet parallel to the bedding; a concordant intrusion
- volcanic neck--feeder pipe of a volcano
types of extrusive bodies
- lava flow--extrusion of lava which flows over the surface of the earth
• fissure--crack in the earth from which a lava flow may form if it is sufficiently fluid and does not emerge from a volcano; it may form a lava plateau
- volcano--cone shaped mound of material extruded from within the earth
• vent--the hole in the earth from which material comes to form a volcano
Igneous Bodies
three types of volcanic cones
- shield cone--basaltic--gentle slope, large base, fluid lava
- cinder cone--small, steep, pile of ash and cinders blown out
- composite cone--intermediate in size and slope with mixed lava and pyroclastic (fire
fragment) debris
types of eruptions
- quiet--non-explosive, basaltic lava, gives off gas, spread, shield
- explosive--volatiles (gaseous material dissolved in the lava)
• crater--depression at center of volcano
• caldera--large crater or where explosion has blown away part of the cone
- intermediate--alternates between quiet and explosive
- fissure--very fluid--produces the lava flow without forming a volcanic cone
products of eruptions
- gasses and vapors
- fragmental
• volcanic bombs--solidify while airborne
• blocks--large
• cinders--medium
• ash and dust--fine
- liquid lava
• aa--blocky
• pahoehoe--smooth ropelike
• pillow
- mud torrents--ash mixes with precipitation to form a flowing mud mass
earthquakes--150,000 a year estimate
seismology--the study of earthquakes
shallow focus 0-20 miles most destructive 95% of all quakes
deep focus 20 - 400 miles 5% of total, 435 miles deepest
Mercalli scale--qualitative Roman numerals, I--XII
Richter scale--quantitative 1-10; effect on seismograph 100 km for epicenter
epicenter--point at earth's surface directly above the focus
distribution
- 1. Pacific Basin (Ring of Fire)
- 2. Mediterranean and trans-Himalayan
- 3. Mid-Atlantic and Mid-Indian Ocean
- 4. African Rift Valley
- 5. Hawaiian Islands
geologic map--shows the rocks at the surface of the earth
block diagram--shows both a surface view and the rocks at depth
cross section--shows the rocks within the earth; the top line is the surface; like looking at a slice cut into the earth
contact--the boundary line between two different rocks (rock units)
reaction to pressure--folding (bending) or faulting (breaking)
Law of Original Horizontality--when sediment is deposited, it is USUALLY deposited in a horizontal layer
•exception--cross-bedding
Law of Superposition--when sediments are deposited, the oldest layer will be found underneath the younger, and they remain this way unless they are overturned
Law of Cross Cutting Relations--when one geologic feature cuts across another, the one which is cut across had to exist beforehand so it is older than the feature which cuts through it
relative dating--dates one event in relation to another
unconformity--a gap in the rock record; erosion has occurred and removed materials form the area and then later more material was deposited on this erosion surface
Relative Dating Diagram 1
anticline--upfold of the rock layers--dip is away from center
syncline--downfold of the rock layers--dip is toward the center
dome--a double upfold of the rock layers
basin--a double downfold of the rock layers
recumbent fold--strongly folded (overturned)
dip--angle between a horizontal plane and a rock layer
strike--orientation in which rock layer is intersected by a horizontal plane, at right angles to the dip direction
differential erosion--it is important to note that the resistance of the rock units is the greatest influence on the topography