Geology and Ecology of Hawaii Exam 1

Lithosphere

Crust and rigid upper mantle

Asthenosphere

Flowing mantle layer, moved by convection currents

Layers of earth- Top down

Crust: continental and oceanic,

mantle: peridotite (iron, magnesium, silica)

Outer core: liquid iron, nickel, possibly oxygen

Inner core: solid iron due to high pressure

Continental Crust

low-density granite (rich in silica and aluminum), older, 20-70km thick

Oceanic Crust

Mostly basalt (rich in iron and magnesium), high density, younger, 6-10 km thick

Rock cycle

Shows transitions btwn rock types, driven by hydrological cycle and earth’s internal heat engine, demonstrates geologic history and rock interconnectivity

Mineral

-naturally occurring pure substance

-specific elemental composition

-3d repeating structure

Rock types

Igneous: form from cooled magma (slow-granite, fast-basalt)

Sedimentary: form from compressed rock fragments (sandstone, Limestone)

Metamorphic: form from altered igneous/sedimentary rocks under heat and pressure (marble, schist)

Mineral classes:

Sulfide

Oxide

Silicate

sulfate

halide

carbonate

phosphate

native element

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Sulfide

Oxide

Silicate

Sulfate

Halide

Carbonate

Phosphate

Native elements

Sulfide: S and metal

Oxide: O and metal

Silicate: Si + O + R

Sulfate: S + O + metal

Halide: Halogen anion (F, Cl, Br, I)

Carbonate: CO3 and metal

Phosphate: PO4 + R

Native elements: Ag, Au, Cu, C

Characteristics used to identify minerals

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Color

Streak

Luster

Cleavage

Hardness

Crystal Structure

Density

Texture

Grain Size

Field Relationship

Color

Streak

Luster

Cleavage

Hardness

Crystal Structure

Density

Texture

Grain Size

Field Relationship

Color- varies due to trace elements

Streak- powder left on unglazed porcelain reveals true color by removing surface variability

Luster: Way light interacts with surface, metallic, glassy, earthy, pearly

Cleavage: Breakage along planes, determined by weaknesses in atomic lattice

Hardness: ability to resist deformation (mohs scale 1-10)

Crystal Structure: determines mineral shape

Density: varies based on atomic structure

Texture: shape/distribution of mineral grains

Field relationships: nearby rocks provide clues about type and origin

Geologic history: Eras

Precambrian era (4.6 bya- 542 mya)

Paleozoic (542-250 mya)

Mesozoic (250-65 mya)

Cenozoic (65 mya- present)

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Geological periods:

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Precambrian:

-Hadean Eon

-Archean Eon

-Proterozoic Eon

Paleozoic:

-Cambrian

-Ordovician

-Silurian

-Devonian

-Carboniferous (Mississippian and Pennsylvanian)

-Permian

Mesozoic:

-Triassic

-Jurassic

-Cretaceous

Cenozoic

-Paleogene

-Neogene

-Quaternary

Precambrian Era

4.6 BYA-542 MYA

Hadean Eon: Earth and moon formed

Archean Eon: Plate tectonics, origin of life

Proterozoic Eon: O2 in atmosphere, sexual reproduction, photosynthesis

Paleozoic Era:

542 MYA-250 MYA

-Cambrian Period: Cambrian explosion, first vertebrates

-Ordovician period: pangea formed, first land plants, mass extinction

-Silurian period: 1st jawed fish, ozone layer

-Devonian Period: 1st forests, seeds, soils, insects and spiders, tetrapods, mass extinction

-Carboniferous: Mississippian: amphibians, limestone formations. Pennsylvanian: conifers, coal-forming swamps

-Permian period: mammal ancestor, 95% mass extinction

Mesozoic Era

250-65 MYA

Triassic: reptiles dominant, pangea starts separating, mass extinction

Jurassic: first birds

Cretaceous: angiosperms, rocky mountains, chalk cliffs of over, dino-killing asteroid

Cenozoic Era

65 MYA-Present

Paleogene: mammals diversify, Himalayas form

Neogene: Grasslands develop, hominids emerge

Quaternary: Ice ages, modern humans, megafauna extinct

Alfred Wegner

Continental drift theory, pangea, plate tectonics

Paleomagnetism

Evidence of variations in earth’s magnetic field

Magnetic anomalies indicate pole shifts

Fe rich minerals in cooling lava align with magnetic field. Preserve field orientation once solidified.

Evidence suggests multiple field reversals

Tectonic/lithospheric plates

14 crust sections floating on earth’s fluid mantle

move 1-15 cm/ yr

Possible mechanism: thermal convection currents in asthenosphere

Collisions lead to mountains and volcanic activity

Earth with no tectonic activity

no new mountains or volcanoes

erosion would flatten and submerge land

no >7 earthquakes

loss of magnetic field leads to atmospheric loss and ocean evaporation

Subduction zones

-dense oceanic crust subducts beneath continental crust

-subducting portion melts as it enters asthenophere

-accretionary wedges form from scraped off material

3 means of mountain formation

Continental convergence:

Subduction

Hot spot mantle plumes:

Continental Convergence

-continental plates collide, crust is crumpled and uplifted

Subduction

-oceanic crust subducts under continental crust

-scraped off material can form mountains

-parallel to accretionary wedge, under continental crust, subducting plate releases hot water, melting rock and creating magma, forming volcanic arc on continental crust

Hot spot mantle plumes

-buoyant magma released from mantle

-erupt as volcano

-carried away from hotspot by moving plate

-volcanoes can become inactive mountains or eroded to form island chains

Life cycle of a Hawaiian island

1. Deep submarine stage

2. Shallow Submarine stage

3. Shield-building stage

4. Post-Shield stage

5. Erosional Stage

6. Rejuvenation stage

7. Reef-growth stage

8. Atoll Stage

9. Guyot (Seamount stage)

Deep submarine stage

-rapid growth because buoyant force of water allows magma to amass at top near extrusion point. >300,000 years

3 components of magma

oxygen, silicon, aluminum

Factors affecting magma viscosity

pressure, temperature, silica polymerization (as temperature drops, silica tetrahedra form and polymerize increasing viscosity), Magma is liquid at >1300 C

Explosive vs Effusive eruptions

Effusive: minor, localized, predictable,

Explosive: eject ash, toxic gas and debris. Quick emptying can cause collapse. landslide and tsunamis.

Role of Gases and Viscosity in explosive eruptions

Less silica: less viscous. erupt in steady flow, gasses can escape-effusive eruption

High Viscosity: under high pressure, gases can’t escape. pressure increases until volcano breaks-explosive eruption

Felsic Rocks

high silica composition, made of light colored minerals like quartz, feldspar, and muscovite mica.

Mafic Rocks

low silica composition, made of dark colored minerals like olivine and biotite

Rhyolite

volcanic, felsic, extrusive. Pink with very fine crystals

Andesite

extrusive, intermediate. Equal amounts of felsic and mafic minerals. Grey, crystals= porphyritic

Basalt

extrusive, mafic.

dark grey, fine grained, porous

phenocrysts=olivine or plagioclase

Pahoehoe v A’a

Pahoehoe: solid sheet of lava

thin surface layer of volcanic glass

extensions=toes

flows smoothly until it drops off and tumbles, breaking into pieces

A’a: rough elements or various sizes. Formed when pahoehoe drops

Volcanic Glass

Columnar Lava

Pillow Lava

Volcanic glass: dark, shiny, opaque product of rapidly cooling basaltic lava

Columnar Lava: upright hexagonal prisms formed by slow cooling and contraction of thick lava flows. 90 degrees to coolest surface

Pillow lava: round masses of hardened lava that extruded into water and quickly hardened without causing steam explosion. Indicate volcano was aquatic at time of eruption.

Shield Volcano

Composite volcano

Calderas

Cinder Cones

Lava Domes

Shield volcano: broad, convex shape. flat summit region. largest volcanoes by volume

Composite volcano: cone shaped. made of alternating strata of solid lithic material and fluid lava at continental plate subduction zones

Calderas: large craters around summit caused by eruption, then collapse

Cinder cones: most common type. steep cones topped by summit crater

Lava domes: small, steep, rough sided

Cascades

subduction, then molten material erupted through continental rock to form a line of volcanoes parallel to coast

Convergent plate boundary eruptions are more explosive

subduction zone/convergent plate boundary eruptions have a higher gas content, which contributes to increased pressure

pressure causes lava to erupt explosively and be carried higher in air

lava is more viscous

at divergent plate boundaries, some lava is used to replace plate material that moved away

Rifting and landslides

heavy volcanic material pushes island down into crust, creating rifts and fault lines

slumps and landslides make up most of islands mass

Bowen’s reaction series

Top: all minerals are molten at 1250c and 1 atm

Bottom: all minerals are solid at 700c and 1 atm

olivine is at top, crystallizes at high temp

Discontinuous: mineral changes at specific temp and constant pressure

Continuous series: changes gradually as conditions are altered

Crystalline structure gets more complex as temp decreases

Lava tubes

Formation: peripheral surfaces of lava cool, inner portion stays hot and fluid.

Trade winds

unequal solar radiation heats equatorial air, driving hadley cell system.

rising air moves toward poles, sinks back to surface at 30 lat, returns to equator

earth’s rotation causes air in N hemisphere to flow from NE-SW otw back to eq, creating NE trade winds- Coriolis effect

Weathering:

-Mechanical

-Chemical

Weathering: the means by which rocks become sediment

-Mechanical: rocks break into smaller pieces due to interactions with ice, water, wind, or other rocks. Increases SA, accelerates chemical weathering

-Chemical: reactions change one type of mineral into another. Allows minerals to become stable at surface.

Ocean tides:

-Spring tides

-Neap tides

Ocean tides:

-moon’s gravity pulls seawater, creating tidal bulges and lowered water on either side- second bulge 180 away

-earth’s revolution pulls land masses thru the bulges and valleys of water, causing tides to rise and fall

SPRING TIDES:

high tides created when moon, earth, and sun are aligned. Suns pull increases size of bulge opposite moon.

NEAP TIDES:

low tides created when sun is 90 degrees to earth and moon

Waves:

Waves: wind and storms move water

little E is lost as a wave travels because affected water only moves a small distance

Feeling bottom- wave motion reaches a depth of half a swell’s wavelength. frictional drag slows swell so crests move closer together and get taller until water collapses as a breaker.

Undertow

Rip Currents

Undertow: backwash of waves moving onto beach, easier to feel in shadows

Rip currents: outward flow of water parallel to shore until a bottom irregularity causes them to flow out to sea.

SAND:

White

Black

Green

White- continental: quartz. Oceanic: calcium carbonate from coral and calcareous algae

Black- contact between lava and seawater creates a steam explosion and particles coated in volcanic glass

Green- fragmented olivine crystals created from erosion of Pu’u Mahana

Shoreline lithic features:

-Sea Stacks

-Blowholes

-Nips

-Sea Cliffs

Sea stacks: Islets formed from partially submerged basalt ridges.

—waves erode part of it, creating a sea cave

—cave extends thru ridge until it forms an arch

—arch roof collapses, remaining portion forms sea stack

Blowholes: roof of a sea cave develops an opening that leads to surface

—waves fill cave or tube, air is compressed, water and air erupt

Nips: sea lvl notches in shore rock caused by waves at constant height hitting rock over a long time

Sea Cliffs: inland part of a nip increases. Rock above collapses and is washed away.

Water’s heat capacity and Hawaii’s climate

water heat capacity moderates temperature adn increases humidity.

pcean absorbs heat by day and releases it at night

heat stored in ocean- evaporation-humidityand rainfall

ocean holds heat from summer radiation

Prevailing trade winds

blow northeast across Hawaii, present most days. gentle and consistent. usually under 25 mph

North pacific high

high pressure systems NE of north pacifc high generates eastward moving storm track

During summer NPH shields Hawaii from storms, not in winter

when low is near hawaii, it causes Kona storms and cold front storms

The inversion layer

the reason there is little rainfall on Hawaii mountaintops.

dry air descends after ascending above the eq and moving N due to hadley cell.

warms as it descends, creating layer with war, atop cold

usually present, weakest during winter (rains then). Prevents precipitation above itself by preventing wet tradewind air from descending

Hilo vs Kailua rainfall

hilo is on eastcoast. trade winds that blow over it are blocked by mauna loa and mauna kea, forcing air to rise and cool above hilo- precipitation. Mountains create upward convection current as they warm, bringin in moist ocean air. Kailua is at similar elevation and position to hilo, but nearest range is smaller and lower

island rainfall:

16% runs off into ocean, 44% evaporates, the rest permeates into groundwater and becomes part of basal lens

Basal lens

-fresh groundwater that floats atop saltwater, permeating base of island

-thickest at abocve sea level at island center, thinner and lower near coast

-hydrostatic pressure created by differnc in elevation causes freshwater discharge from subaerial adn submarine springs

-at equilibrium when amount lost to ocean=amount added

-some heated by volcanic activity and becomes hot springs

Groundwater

-porosity

-permeability

-perched water

porosity: quantity of gaps or pores between bits of sediment that allow water to enter

permeability: when pores in a substanve are sonnected and unobstructed, allowing water to move thru

layers of caldera-fillin

Perched water: water that collects in low-permeability area, can be extractd thru wells or tunnels

Soik and rainfall

More rainfall-may be more fertile, could be leeched

-well-draining can prevent swamp

-arid mountaintops may be more rich in salts and water soluble minerals

-fertile and well-drained=good for crops