Elemental Composition of Crust

Element Composition of crustal rocks
Oxygen 46.2%
Silicon 27.7%
Aluminum 8.1%
Iron 5.0%
Calcium 3.6%
Sodium 2.8%
Potassium 2.5%
Magnesium 2.1%
Other elements 1.7%

Flood Basalts and Stratigraphic Boundaries

Flood Basalts and Stratigraphic Boundaries

The great continental flood-basalt lava flows exceeded 2000 cubic kilometres and comprise one form of large igneous province (LIP map). [image Columbia River Basalt Flows] Large igneous provinces are believed to have been caused by mantle plumes in the lithosphere, which injected magma into the lithosphere and erupted as huge basalt lava flows, probably within a million years or less.

The Deccan, Newark, and Siberian flood basalts (each with lava volumes greater than 2 x 10^6 km^3 over periods of 1 million years or less) have been correlated with major extinction events. Extinctions could have been caused by environmental impacts of released gases – climatic cooling due to sulphuric acid aerosols, greenhouse warming caused by CO2 and SO2 gases, and acid rain. Mantle plume activity and flood basalts may also have been associated with other deleterious global geological factors, such as changes in sea-floor spreading rates, rifting events, increased tectonism and volcanism, or sea-level variations.

The end-Cretaceous (Cretaceous/Tertiary or K/T boundary) mass extinction that wiped out the dinosaurs has been correlated with the impact of a 10-km diameter asteroid about 65 million years ago. Several other extinction events correlate with evidence of similar impacts.

Flood Basalt

Age Ma

Stratigraphic Boundary

Age Ma

Columbia River 0.25 x 10^6 km^3

16 ± 1 duration ~ 1 Myr Early/Mid-Miocene [image] 16.4
Ethiopia ~1 x 10^6 km^3 31 ± 1 duration ~ 1 Myr Early/Late Oligocene 30

North Atlantic >1 x 10^6 km^3

57 ± 1 duration ~ 1 Myr Paleocene/Eocene(Thanetian/Selandian) 54.8 (57.9)
Deccan >2 x 10^6 km^366 ± 1 duration ~ 1 MyrCretaceous/Tertiary [image]65.0 ± 0.1
Madagascar ? volume 88 ± 1 duration ~ 6? Myr Cenomanian/Turonian(Turonian/Coniacian)

93.5 ± 0.2 (89 ± 0.5)

Rajmahal ? volume 116 ± 1 duration ~ 2 Myr Aptian/Albian 112.2 ± 1.1
Serra Geral/Etendeka >1 x 10^6 km^3 132 ± 1 duration ~ 1 or 5 Myr Jurassic/Cretaceous(Hauterivian/Valanginian) [image 1] 142 ± 2.6 (132 ± 1.9)
Antarctica >0.5 x 10^6 km^3 176 ± 1 or 183 ± 1 duration ~ 1? Myr (Aalenian/Bajocian) (176.5 ± 4)
Karoo > 2 x 10^6 km^3 td> 183 ± 1 duration ~ 0.5 -1 Myr Early/Middle Jurassic [image 1, image 2] 180.1 ± 4
Newark >2? x 10^6 km^3201 ± 1 duration ~ 0.6 MyrTriassic/Jurassic [images]205.7 ± 4
Siberian > 2 x 10^6 km^3249 ± 1 duration ~ 1 MyrPermian/Triassic [image, image 2]248.2 ± 4.8

adapted from here.

Other flood basalts Paraña,

Geological Time Overview




The Precambrian extends through the Hadean, Archean, and Proterozoic Eons. The Phanerozoic commences with the Cambrian.

Hadean Eon : 4.6 - 3.8Ga

Archean Eon : 3.8 - 2.5 Ga

3.8-3.6 Ga Eoarchean
3.6-3.2 Ga Paleoarchean
3.2-2.8 Ga Mesoarchean
2.8-2.5 Ga Neoarchean

Proterozoic Eon : 2.5 Ga ~ 542 Ma

2.5-1.6 Ga

Paleoproterozoic Era

Siderian 2.5-2.3
Rhyacian 2.3-2.05
Orosinian 2.05-1.8
Stratherian 1.8-1.6
1.6-1.0 Ga Mesoproterozoic Era Calymmian 1.6-1.4
Ectasian 1.4-1.2
Stenian 1.2-1
1.0 Ga-542 Ma Neoproterozoic Era Tonian 1.0 Ga -850 Ma
Cryogenian 850-635 Ma
Vendian or Ediacaran, 635-542

Phanerozoic Eon : 542 Ma - present

542-251 Ma Paleozoic Era Cambrian 542-488.3
Ordovician 488.3-443.7
Silurian 443.7-416
Devonian 416-359.2
Carboniferous 359.2-299.0 Mississippian and Pennsylvanian
Permian 299-251
251-65.5 Mesozoic Era Triassic 251-199.6
Jurassic 199.6-145.4
Cretaceous 145.4-65.5




65.5-present Cenozoic Era Paleogene 65.5-23.03 Paleocene 65.5-55.8

Eocene 55.8-33.9 : ends with Grande Coupure extinction event

Oligocene 33.9-23.03 : climate cooling begins by end of epoch
Neogene 23.03-present

Miocene 23.03-5.332

Pliocene 5.332-1.806

Pleistocene 1.506-.005

.005- present

Labels: , , , , , , , , , , , , , ,

Geological Time

Eon/time Era Period / comment Epoch / comment

Hadean Eon : 4.6 - 3.8Ga

Archean Eon : 3.8 - 2.5 Ga

3.8-3.6 Ga Eoarchean





stromatolite reefs

3.6-3.2 Ga Paleoarchean
3.2-2.8 Ga Mesoarchean
2.8-2.5 Ga Neoarchean

Proterozoic Eon : 2.5 Ga ~ 542 Ma

2.5-1.6 Ga

Paleoproterozoic Era

Siderian 2.5-2.3

evolution of oxygenic photosynthesis

continents stabilized

Rhyacian 2.3-2.05
Orosinian 2.05-1.8
Stratherian 1.8-1.6
1.6-1.0 Ga Mesoproterozoic Era Calymmian 1.6-1.4

Rodinia starts to assemble

evolution of sexual reproduction

Ectasian 1.4-1.2
Stenian 1.2-1
1.0 Ga-542 Ma Neoproterozoic Era Tonian 1.0 Ga -850 Ma

glaciations dubbed "Snowball Earth"

earliest multicelled fossils

Cryogenian 850-635 Ma
Vendian or Ediacaran, 635-542

Phanerozoic Eon : 542 Ma - present

542-251 Ma Paleozoic Era Cambrian 542-488.3

Cambrian "explosion"


Ordovician 488.3-443.7

began and ended (2nd largest) with extinction events: graptolites, first jawed fish, land plants

Gondwana, Taconinc orogeny

Silurian 443.7-416

Named for Wales. Euramerica and Caledonian orogeny

graptolites, coral reefs, first bony fish, Myriapods were first terrestrial animals, first vascular plants; eurypterids; brachiopods, bryozoa, molluscs, and trilobites abundant in warm seas

Devonian 416-359.2 "Age of Fishes", first sharks, first ammonites; land - first tetrapods, insects, spiders, and seed-bearing plants
Carboniferous 359.2-299.0

Pangaea assembling, Hercynian and Alleghanian orogenies

Mississippian and Pennsylvanian separated by an unconformity: cyclothemic coal deposits, widespread epicontinental seas and carbonate depostion.

Insect and amphibian gigantism. Foraminifera prominent.

Permian 299-251


Permian-Triassic extinction event (largest) with loss of 90% to 95% of marine species and 70% of all land organisms

251-65.5 Mesozoic Era Triassic 251-199.6 starts and ends with extinction events, adaptive radiation after P-T extinction; angiosperms, pterosaurs
Jurassic 199.6-145.4

Pangaea break-up

"Age of Dinosaurs"

Cretaceous 145.4-65.5

Named for chalk (coccolith) deposits of France and South England

K-T boundary extinction event - Chicxulub impact crater

65.5-present Cenozoic Era Paleogene 65.5-23.03 Paleocene 65.5-55.8 (mammals)

Eocene 55.8-33.9 : ends with Grande Coupure extinction event

first modern mammals

Oligocene 33.9-23.03 : climate cooling begins by end of epoch
Neogene 23.03-present

Miocene 23.03-5.332

Horses, mastodons, first apes

Pliocene 5.332-1.806

Australopithecus, Homo habilis

Pleistocene 1.506-.005

glaciations, megafauna, anatomically modern humans

.005- present

end of recent glaciation, rise of civilization

Labels: , , , , ,

Lagerstätten & Biota

Lagerstätten are fossil beds that contain particularly well preserved fossils.






Doushantuo Lagerstätte Neoproterozoic, Vendian South China phosphatized microbial pseudomorphs [1]: algal thalli, acritarchs, and globular microfossils interpreted as animal embryos [2] (peripatus)
Ancient Stromatolite Reefs Northern Canada possesses some of the best preserved examples of Proterozoic reefs and other carbonates anywhere in the world. .[Precambrian pinnacle reef, NWT ; Steep Rock Stromatolites]
Ediacara Biota, Ediacara, Australia Ediacara Hills (SA); White Sea (Russia); Mistaken Point Formation (Nfld, Canada); Charnwood Forest, UK; South America, Namibia, South China

Cambrian Lagerstätten

Sirius Passet Formation Early Cambrian, 515-520 Ma Greenland oldest of major Cambrian lagerstätten (peripatus)

Chengjiang Lagerstatte,


Lower Cambrian, 515 to 520 Ma Yunnan Province, China: Qiongzhusi Formation soft-tissue fossils of algae, medusiform metazoans, chondrophorines, sponges, chancelloriids, ctenophores, cnidarians, nematomorphs, priapulid worms, hyoliths, possible ectoprocts, inarticulate brachiopods, annelid-like animals, anomalocharidids, onychophorans, arthropods, occassional trilobites, echinoderms, ‘hemichordates’ and probable early chordates
Burgess Shale Middle Cambrian, 505 Ma BC, Canada
Wheeler Shale Middle Cambrian Utah, USA: House Range University of California, Berkeley, web page
Andrarum Limestone Middle Cambrian Sweden
'Orsten' Late Cambrian Sweden


Beecher’s Bed Early Ordovician Utica, NY state, USA
Soom Shale Late Ordovician Cape Province, South Africa [1] Soom Shale, South Africa


Much Wenlock Limestone Early Silurian Wales 600 species of well-preserved invertebrates: crinoids, corals, brachiopods, trilobites, algae and bryozoans
Ludford Lane Bonebed Early Silurian Shropshire, Welsh Borderlands oldest known terrestrial ecosystem : vascular plants, centipedes, kampecarid myriapods, arthropleurid, trigonotarbid, arthropod fragments
Fiddler’s Green Formation Early Silurian NY state, USA eurypterid beds
Waukesha [1] Early Silurian Llandovery-Wenlock Wisconsin, USA arthropods and conodonts [1]
Lesmahagow Middle Silurian Scotland arthropods and fish


Rhynie Chert Early Devonian Scotland hot spring deposits
Hunsrück Shale(Hunsrückschiefer) Early Devonian (Late Pragian to Early Esmian) Rhine and Moselle Valleys,
Gilboa Middle Devonian NY state, USA spiders and pseudoscorpions
Escuminac Bay Late Devonian (Early Frasnian) Eastern Canada anaspids, placoderms, and other fishes including Eusthenopteron
Canowindra Late Devonian NSW, Australia fish
Cleveland Shale Late Devonian (Fammenian), 360 Ma Ohio, USA vertebrate sharks
Gogo Formation Upper Devonian (Frasnian), 350 Ma The Kimberley, NW Australia placoderm fish


East Kirkton Early Carboniferous Scotland hot spring deposits; plants; arthropods (scorpions); amphibians and reptiles
Scottish ‘Shrimp Beds’ Early Carboniferous Scotland crustaceans, conodont animals, tomopterid worms, fish
Loch Humphrey Burn Early Carboniferous Southern Scotland terrestrial : several successive plant bearing horizons within a volcanic terrain
Mazon Creek Late Carboniferous Illinois, USA deltaic and near-shore marine
Karoo Late Carboniferous to Triassic Southern Africa rich mammal-like reptile fauna from the Beaufort Sandstone


Wellington Shale Early Permian Kansas, USA insects


Gres à Voltzia Triassic France deltaic deposits; terrestrial plants, insects, plus aquatic crustaceans and fish


Posidonia Shale Early Jurassic Germany
Posidonienschiefer, Holzmaden Early Jurassic Germany fossil reptiles - noteably ichthyosaurs, crustaceans, cephalopods
Karatau Jurassic South Kazakhstan insects, spiders, crocodiles, salamander, lizard, fish, pterosaurs, plants
Christian Malford Middle Jurassic England squids
Stonefield Slates Middle Jurassic Oxfordshire, England small mammal jaws and teeth
La Voulte-sur-Rhône Middle Jurassic (Lower Callovian) ~ 160 Ma Ardèche, France allochthonous benthic and nektobenthic, and in situ bivalve
Purbeck Beds Late Jurassic England insect fauna including dragonflies, locusts, grasshoppers, butterflies, ants and aphids
Morrison Formation Late Jurassic Wyoming and Colorado, USA
Solnhofen Limestone Late Jurassic(Lower Titonian) Germany fine-grained lagoonal sediments; most famous for the Archeopteryx and Compsognathus fossils


Santana Formation Cretaceous Brazil fossil fish and pterosaurs
Sierra de Montsech Cretaceous Spain fossil spiders, insects, crustaceans and vertebrates
Pierre Shale Cretaceous (Campanian) North Dakota, USA arthropods, vertebrates, including mosasaurs
Hajoula Limestone Cretaceous Lebanon fossil arthropods and fish

Liaoning Lagerstätte, Yixian Formation

Cretaceous (Barremian?), 120-150 Ma Liaoning Province, China: Yixian Formation true birds, dinosaurs, ‘feathered dinosaurs’
Las Hoyas Lower Cretaceous (Barremian), 121-127 Ma Cuenca, Spain rich terrestrial and freshwater assemblage of invertebrate and vertebrate trace fossils, early angiosperms, ferns, cycads, conifers, insects, birds, fish, crocodiles, a dinosaur, amphibians and lizards
Tlayúa Early Cretaceous, 100 Ma Mexico coral reef : fishes, foraminifera, sponges, gorgonids, bivalves, gastropods, belemnites, ammonites, echinoderms, crinoids, annelids, arthropods, arachnid, anispoterus, turtles, pleurosaurs, sphenodonts, lizards, crocodiles and pterosaurs


Green River Formation Eocene Wyoming, USA lacustrine fossil fish and other vertebrates
Monte Bolca Eocene, 52 Ma Italy tropical marine lagoon: fishes, plants, insects
Princeton Chert Middle Eocene, 49 mya BC, Canada permineralised flora
Grübe Messel Shale Eocene Germany lacustrine fossil plants, vertebrates and insects


Florissant formation Late Oligocene - Early Eocene Colorado, USA trees, plants, insects
Riversleigh Fossil Sites Late Oligocene (25ma) to Middle Miocene (10ma) to present Queensland, Australia mostly vertebrates, with a few snails and insects

Pliocene/ Pleistocene

Lake Turkana Pliocene/ Pleistocene, 4-0 Ma Lake Turkana Basin, Kenya, East Africa Australopithecus and Kenyanthropus, and Homo







Soom Shale

Karoo System

Lake Turkana, Kenya

Proterozoic (Vendian)

Late Ordovician

Late Carboniferous to Triassic

Pliocene/ Pleistocene, 4-0 Ma

Brazil Santana Formation Cretaceous

Ediacara Hills Biota, Ediacara, Australia

Gogo Formation


Proterozoic (Vendian)

Upper Devonian (Frasnian), 350 Ma

Late Devonian


Ancient Stromatolite Reefs

Mistaken Point Formation, Nfld.

Burgess Shale

Escuminac Bay


Proterozoic (Vendian)

Middle Cambrian, ~505 Ma

Late Devonian (Early Frasnian)


Doushantuo Formation

Chengjiang Lagerstätte

Jehol Group

Yixian Formation (Liaoning)

Proterozoic (Vendian)

Early Cambrian, 515-520 Ma

Early Cretaceous

Cretaceous (Barremian?)


Charnwood Forest Vendian Biota

Christian Malford

Stonefield Slates

Purbeck Beds

Proterozoic (Vendian)

Middle Jurassic

Middle Jurassic

Late Jurassic


Gres à Voltzia

La Voulte-sur-Rhône


Middle Jurassic (Lower Callovian) ~ 160 Ma


Hunsrück Shale (Hunsrückschiefer)

Posidonia Shale


Solnhofen Limestone

Grübe Messel Shale

Early Devonian (Late Pragian to Early Esmian)

Early Jurassic

Early Jurassic

Late Jurassic (Lower Titonian)


Greenland Sirius Passet Formation Early Cambrian, 515-520 Ma
Italy Monte Bolca (Mt. Bolca): Musei della Lessinia web page Eocene
Kazakhstan Karatau Jurassic
Lebanon Hajoula Limestone Cretaceous
Mexico Tlayúa Early Cretaceous, 100 Ma
Russia Vendian Biota, (White Sea) Proterozoic (Vendian)


Rhynie Chert

East Kirkton

Scottish ‘Shrimp Beds’

Loch Humphrey Burn

Middle Silurian

Early Devonian

Early Carboniferous

Early Carboniferous

Early Carboniferous

South America

Vendian Biota

Proterozoic (Vendian)

Sierra de Montsech

Las Hoyas


Lower Cretaceous (Barremian), 121-127 Ma


Andrarum Limestone

'Orsten' Beds

Middle Cambrian

Late Cambrian


Wheeler Shale

‘Beecher’s Bed’

Fiddler’s Green Formation



Cleveland Shale

Mazon Creek

Wellington Shale

Morrison Formation

Pierre Shale

Green River Formation

Middle Cambrian

Early Ordovician

Early Silurian, 425 Ma

Early Silurian

Middle Devonian

Late Devonian (Fammenian)

Late Carboniferous

Early Permian

Late Jurassic

Cretaceous (Campanian)



Much Wenlock Limestone Formation

Ludford Bonebeds

Early Silurian

Early Silurian

Also Dominican Amber :

Labels: , , , , , , , , , ,

Minerals & Rocks: Minerals


mineral / chemical formula

properties / significance


magnetite (lodestone)Fe2O3 black ferrimagnetic mineral in the spinel group, converts to hematite on oxidation, produced from peridotites and dunites by serpentinization. most igneous rocks and metamorphic rocks, many sedimentary rocks, widespread ore deposits, banded iron formations

quartz (silica) SiO2

[gallery, 2, 3]

silica tetrahedra, tectosilicate, hexagonal rhombohedral crystals in numerous varieties named for color and microstructure, numerous growth forms commonest mineral, igneous, sedimentary, and metamorphic rocks, hydrothermal veins and pegmatites, granite, sandstone, limestone


Minerals & Rocks: Carbonates

Carbonates of iron, sodium, calcium, and calcium/magnesium:
Composition Formula Mineral name Rock
iron carbonateFeCO3SideriteIronstone
sodium bicarbonateNaHCO3Baking sodaNahcohlite
calcium carbonateCaCO3CalciteLimestone
calcium, magnesium carbonate(Ca, Mg)CO3DolomiteDolostone

Minerals & Rocks: Evaporates, Sulphates

Evaporation of brines and salines results chemically deposited rocks, including:
Composition Formula Mineral Rock
hydrated calcium sulfateCaSO4 & 2H2OSeleniteGypsum
sodium chlorideNaClHaliteRock salt

Minerals & Rocks: Metamorphic

Metamorphic rocks result from the subjection of a protolithic parent rock (igneous, sedimentary, or metamorphic) to heat and/or pressure and/or chemically active fluids. Metamorphic rocks are classified according to the parent rock and the degree of deformation to which the rocks have been subjected. Metamorphism occurs locally (contact) or on a large scale (regional).

Sedimentary rock Metamorphic product (low to high grade)

Meta-conglomerate, schist, gneiss

Breccia Meta-breccia, schist, gneiss
Sandstone Quartzite, mica schist
Shale/siltstone/claystone Phyllite, slate, schist, gneiss, "fubarite"
Limestone/dolostone Marble (color shows "argillaceous" or "carboniferous")
Black shale Black slate
Peat/coal Anthracite through graphite with or without associated natural gas, petroleum and asphalt; Mississippi-type lead and zinc deposits

Chemical metamorphic rocks:

CompositionMineral NameRock Name/Ore
Au Gold Gold Ore
Ag Silver Silver Ore
Cu Copper Copper Ore
Pt PlatinumPlatinum Ore
S Sulfur Native Sulfur

Deposition of metals results from regional metamorphism, volcanism, hydrothermal vents, and sulphide solutions:

CompositionMineral NameRock Name/Ore

Solutions of hot water chemically alter carbonates and silicates:

CompositionMineral NameRock Name
SiO2 transparent...Quartz, rock crystal
SiO2 translucent...Jasper, flint, chert, quartz, chalchedony, agate, silicified fossils, petrified wood
CaCO3CalciteTravertine marble, geodes, stalactites/stalagmites

Labels: , , , , , ,

Minerals & Rocks: Oxides

Oxides form as a result of chemical weathering (by oxygen and water) of iron and aluminum containing minerals:
Composition Formula Mineral name Rock name
iron oxide Fe2O3 Hematite Iron ore
iron oxide Fe3O4 Magnetite/Lodestone Iron ore
hydrated iron oxide 2Fe2O3 & 3H2O Limonite Rust/iron ore
hydrated aluminum oxide Al2O3 & 2H2O Bauxite Aluminum ore
aluminum oxide Al2O3 Corundum Ruby/sapphire

Radiometric Dating

Radiometric dating employs known rates of radioactive decay from a radioactive parent to its stable daughter element to estimate the age of a sample.

Mass number is the total number of protons plus neutrons in an isotope of an element. α-decay reduces the mass number by 4, β-decay does not alter mass number (K-40 → Ar-40), γ-decay reduces mass number by 1.

Elements may decay from radioactive parent to stable daughter through intermediate isotopes in a decay chain called a radioactive series. For the purposes of geological radiometric dating, ratios of radioactive-parent : stable-daughter provide sufficient information to estimate the length of elapsed time since an igneous rock containing radioactive elements cooled and solidified from magma or lava.

Each radioactive isotope (atoms of the same element differing in neutron number) has its own unique half-life, which is the time required for half of the parent radioactive element to decay to a daughter product. Radioactive decay occurs at a constant exponential or geometric rate, so half of parents will decay to daughters (1:1) in one half life and one half of the remaining parents will decay in the next half life (1:3).

Geologists estimate the length of time over which decay has occurred by measuring the ratio of radioactive parent element and stable daughter elements. Radioactive elements tend to become concentrated in the residual melt during the crystallization of igneous rocks, so traces of a radioactive mineral in an igneous rock will 'set the clock' at the time of cooling/solidification.

Radioactive elements and half-lives

radioactive parent

stable daughter


Sm-147 Nd-143 106 billion years
Rb-87 Sr-87 48.8 billion yrs
Re-187Os-18742 billion yrs
Lu-176Hf-17638 billion yrs
Th-232 Pb-208 14 billion years
U-238 Pb-206 4.47 billion years
K-40 Ar-40 1.26 billion yrs
U-235 Pb-207 704 million years
Be-10B-101.52 million yrs
Cl-36Ar-36300,000 years
U-234Th-230248,000 years
Th-230Ra-22675,400 years
C-14 N-14

5715 years = useful on materials less than 70,000 years old.

Labels: , , , , , ,

Tectonic Plate Boundaries

The lithosphere is divided into tectonic plates (im) that move, albeit very slowly, in relation to each other – converging, diverging, riding over/under one another, and sliding past one another.

type of boundary

associated phenomena and structures

converging plates

arc-continent (ocean-ocean)volcanic island arc, volcanoes, submarine trench, folding and faulting, subduction zone
ocean-continentsubmarine trench, magmatic arc, folding and faulting, subduction zone
continent-continentfolding and faulting, orogeny

diverging plates

ocean-oceanmid-ocean ridges (spreading centers, im, Iceland), volcanoes
continent-continentrift valleys, volcanoes

subduction zones

arc-continent volcanic island arcs, very deep earthquakes
ocean-continentvolcanic chains, very deep earthquakes

transform-boundary faults (im)

ocean-oceanshallow earthquakes, strike-slip faults
continent-continentshallow earthquakes, strike-slip faults

Labels: , , , ,

Weathering of Minerals

The mode of weathering influences the minerals that are formed from weathering of rocks.
Mineral Physical weathering Chemical weathering
Quartz sand-sized particles soluble silica
Feldspars/micas clay-sized particles soluble salts/soluble silica
Fe+/Mg+ black sands soluble Fe+ and Mg+ ions

Labels: ,


Volcanoes form where heated material escapes from the Earth's crust.

Type of eruption named for

Features structure; ejection; effusion

gas/silica content of lava


Hawaiian island shield volcanoes

spatter cones and ramparts; very broad, flat lava cones; very weak ejection of fluid blobs, cow-dung bombs and spatter, very little ash; followed by often extensive flows of low viscosity (fluid) lava low gas/low silica
Basaltic flood spatter cones and ramparts; very broad, flat lava cones, lava plains; very weak ejection of fluid blebs and cow-dung bombs and spatter, very little ash; followed by voluminous, wide-spread flows low gas/low silica



cinder cones; weak to violent ejection of pasty fluid blebs, spherical to fusiform bombs; cinder; small to large amounts of glassy ash; thicker, less extensive flows of moderately fluid lava; flows may be absent ↓ increasing gas/higher silica



Soufriere Hills

ash cones, block cones, block-and-ash cones; moderate to violent ejection of solid hot fragments of new lava; essential, glassy to lithic, blocks and ash, pumice; lava viscous, so flows commonly absent, thick and stubby if present, ash flows rare


Mt. Pelee

ash and pumice cones; domes; explosive activity like Vulcanian, commonly with glowing avalanches; domes and/or short, very thick flows of viscous lava; flows may be absent


Pliny the Elder, who died during the eruption of Vesuvius

widespread pumice lapilli and ash beds; generally no cone-building; ejection of large volumes of ash, with accompanying caldera collapse, ejecta are glassy ash and pumice; magma very viscous, so ash flows, small to very luminous, or effusive activity may be absent
Rhyolitic flood flat plain, or broad, flat shield, often with caldera; relatively small amounts of ash projected upward into the atmosphere; ejecta are glassy ash and pumice; viscous magma, so effusive activity confined to relatively small amounts of ash projected upward into the atmosphere Rhyolite
Ultravulcanian block cones; block-and-ash cones; weak to violent ejection of solid fragments of old rock; ejecta are accessory and accidental block and ash; no magma and no lava effusion
gas eruptions continuous or rhythmic gas release at vent; no ejecta or very minor amounts of ash, no magma
fumarolic generally no structure, rarely very small ash cones; no ejecta or rarely very minor amounts of ash; no magma, nonexplosive weak to moderately strong long-continued gas discharge

Labels: , , , , , , , ,

. . . since 10/06/06