geo exam4

What does crust type have to do with oceans?

Compared to continental crust (composed of a lot of granite), oceanic crust is more dense, thinner, and younger.

About how much of the Earth’s surface is covered by ocean

70.8%

is the ocean the deepest in the center

no

How do we describe water depth?

- bathymetry, variation of depth

How does the bathymetry vary as you move from land to the center of the ocean (passive vs. active margins) 

• PASSIVE MARGIN. It begins to get deeper and deeper but slowly (continental slope) has abyssal planes

• ACTIVE MARGIN When you reach the shelf break is when it gets deep very quickly (continental shelf) has seamounts

abyssal plain.

the lithosphere moves away from the mid-ocean ridge spreading centers it cools down and sinks. then is flat

seamounts

Hot-spot volcanoes (not plate boundary related) that do not rise above sea level

salinity

the measure of all the salts dissolved in water typically expressed in parts per thousand (PPT)

• Average in ocean about 35

Why does salinity vary?

• Water Temperature: warmer water can hold more salt. Like sugar and sweet tea 

• Addition of fresh water from river runoff, ground water, ice melt, direct rain. These are all fresher water that can bring the salinity down 

• Evaporation rate at oceans surface, taking away water leaving behind more salt

Solar Radiation Reaching Earth

Less solar radiation around north and south pole causing the water to be colder and then warmer around the equator due to more solar radiation

Current

 well-defined stream of ocean water

• Surface current:

• are caused by interaction between wind and the surface of water. Only affects the upper few hundred meters of water.

Deep Currents: 

are also influenced by wind due to zones of upwelling and downwelling

Upwelling- water being pushed to the left and up

Downwelling- water being pushed to the right and down

Coriolis effect

-– The deflection of objects, winds, and currents on the surface of the Earth owing to the planet’s rotation

Gyre

A large, circular flow pattern of ocean surface currents 

Thermohaline circulation

– the rising and sinking of water driven by contrasts in water density which is due in turn to differences in temperature and salinity; this circulation involves both surface and deep water currents in the ocean

What causes ocean tides?

The larger tidal bulge is on the side closest to the moon and the smaller tidal bulge is on the other side so it develops as the earth spins relative to the two

Tidal reach (range)

– the elevation difference between sea level at high tide and low tide.

How does wave energy vary with water depth? 

Energy decreases with depth

wave action

shear of wind blowing over the water surface

Wave morphology

• Crest - top of wave

• Trough - low area between waves.

• Wave base - the level (in depth) to which a wave affects the water

Wave parameters

• Wave height – distance between trough and crest

• Wavelength – horizontal distance between crests

Wave refraction

- the bending of the waves as they approach the shore at an angle (refraction basically equals bending).

Coast

– the belt of land bordering the sea

Longshore current

- moves parallel to the shore. Water current going the direction of the wind

Longshore drift

– the movement of sediment laterally along a beach; it occurs when waves wash up a beach diagonally

Groin

– a concrete or stone wall built perpendicular to a shoreline in order to prevent longshore drift from removing sand

water table

 the boundary, approximately parallel to the Earth’s surface, that separates substrate in which groundwater fills the pores from substrate in which air fills the pore

Stream

– a ribbon of water that flows in a channel

Drainage network (basin)

– an array of interconnecting streams that together drain an area

• There are 5 common types of drainage networks: dendritic, rectangular, trellis, radial, and parallel

what controls the type of network that will develop?

The geology, rock type

Drainage divide

a highland or ridge that separates one drainage basin (network) from another

Permanent streams

• Water flows all year

• • Bed/floor of channel is at or below the water table

• • Humid or temperate climates

• • Sufficient rainfall

• • Low evaporation

• • Discharge varies seasonally

Ephemeral Streams

• Do not flow all year

• • Bed/floor of channel is above the water table

• • Dry climates

• • Low rainfall

• • High evaporation

• • Flows mostly during rare flash floods

Laminar vs. Turbulent flow 

• Laminar  occurs when a fluid flows in parallel layers, with no disruption between the layers

• Turbulent a flow regime characterized by chaotic property changes

How do streams erode?

Scouring – running water removes loose fragments of sediment 

Breaking and lifting – running water can break clasts of solid rock off the channel floor or walls 

Abrasion – running water containing sand to gravel size particles that act like sandpaper and grinds away at the channel floor or walls 

Dissolution

– running water dissolves soluble minerals as it passes and carries the minerals away in solution

Geologists refer to the total volume of sediment carried by a stream as its sediment load.

Bed load

– larger solid particles (sand, pebbles, or cobbles) that bounce or roll along stream floor

Suspended load

– small solid particles (silt or clay size) that swirl along in the water without settling to the floor of the channel

Stream competence

Stream capacity

Stream competence – refers to the maximum particle size a stream can carry 

Stream capacity – refers to the total quantity of sediment it can carry (depends on competence and discharge)

What conditions (high/low energy, fast/slow water) propose sediment erosion/transportation and sediment deposition?

High energy (fast moving water) = sediment erosion/transportation

 Low energy (slow moving water) = sediment deposition

• Water flow rates (energy) decreases when?

• a stream/river reaches a water body (ocean). When this happens, the larger clasts are deposited first, then medium size clasts (sand), and finally small clasts (silt/clay). Sorting occurs.

Delta

– a wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out 

Stream gradient

– the slope of a stream’s channel in the downstream direction

Longitudinal profile

A cross-section image showing the variation in elevation along the length of a river

 Base level

– The lowest elevation a stream channel’s floor can reach at a given locality 

Ultimate base level is sea level (sea level can move up and down) A lake (natural or man-made) represents a local base level 

A stream “tries” to erode down to base level (slow process)

Meander

– A snake-like curve along a stream’s course

Braided stream

– A sediment-choked stream consisting of entwined sub-channels.

channel

an elongate depression or trough through which a stream flows

Groundwater

– water that resides under the surface of the Earth, mostly in pores and cracks of rock or sediment

 Karst landscape

– a region by underlain by caves in limestone bedrock; the collapse of the cave creates a landscape of sinkholes separated by higher topography; or of limestone spires separated by low areas

Porosity

– the total volume of empty space (pore space) in a material, usually expressed as a percentage, pores can become filled with water

Permeability

– the degree to which a material allows fluids to pass through it via an interconnected network of pores and spaces

Water table

– the boundary, approximately parallel to the Earth’s surface, that separates substrate in which groundwater fills the pores from substrate in which air fills the pores 

Unsaturated zone

– the region of the subsurface above the water table, pore space may contain some water and some air 

Saturated zone

– the region below the water table where pore space is filled with water

Aquifer

– sediment or rock that transmits water easily (has high porosity and permeability)

Aquitard

– sediment or rock that does not transmit water easily and therefore retards (slows down/stops) the motion of water (typically has both low porosity and permeability)

- Confined aquifer – an aquifer that is separated from the Earth’s surface by an overlying aquitard

- Unconfined aquifer – an aquifer that intersects the surface of the Earth

Infiltrate

seep down into 

Recharge area

Discharge area

Recharge area – a location where water enters the ground and infiltrates down to the water table

Discharge area – a location where groundwater flows back up to the surface, and may emerge at springs

Artesian well

– a well in which water rises on its own (due to angled bedrock and natural pressure within the system)

What happens when the water table intersects that Earth’s surface?

Water flows from the ground to the land surface. Water changes from groundwater to surface water.

Travertine

– A rock composed of crystalline calcium carbonate formed by chemical precipitation from groundwater that has seeped out at the ground surface.