unit 2 - gradational processes

weathering

weathering

• the forces that essentially break down the surfaces on our earth

• the breaking down of rock into smaller particles

• 2 types: physical (mechanical) or chemical

frost shattering

• physical weathering

• water enters pores or joints in a rock and as it freezes, expands, and cracks it

thermal expansion

• physical weathering

• common in desert regions where temps. fluctuate

• during the day, the rocks get very hot and expand, but a night they become cool which causes them to contract (shrink) and cracks them

erosion

• the movement of original sediments

• the process by which soil and rock particles are worn away and moved elsewhere by gravity, wind, water or ice

deposition

• the depositing or laying down of sediments

• geological process where sediments, soil and rocks are deposited

mass wastage

• gravity exerting a downward pull on weathered particles

landslide

• rapid sliding of large rock masses as they “separate” from the slope

one method for stabilizing mass wastage

• long bolts (fastened into bedrock) = stabilizes soil and slope above

river stages/lifecycle

• young stream (steep slope), mature stream (moderate slope), old stream (gentle slope)

youthful stage

• deep cutting, v-shaped valleys

• fast flowing

• high erosion BUT low deposition (too fast!)

• generally flows in a fairly straight direction

• associated with rapids and waterfalls

mature stage

• flood plains have begin to form on either side of the river

• riverbed tends to get wider and meandering begins (squiggling)

• flow slows to a moderate speed

• deposition is taking place

old stage

• a lot of meandering

• river widens and is much more shallow

• deltas are being formed

• deposition is everywhere!

erosional action from rivers

hydraulic action

forces of water flowing in the river loosens sediment/rocks in the riverbed and carries them downstream and deposits when flow diminishes

abrasion (aka corrasion)

debris such as sand can act as powerful abrasion agent against river banks and beds (think polishing)

attrition

fast moving water (like a flood) picks up rocks, moves them along striking other rocks and breaking them apart

solution

minerals from rocks dissolve in water and create their own solution

suspension

very light material is carried along in the water and doesn’t touch the bottom (floating in air)

saltation

particles that are heavy bounce down the river bed

traction

heavy particles are dragged along the bottom of the river bed

features of rivers

oxbow lake

formed when a river “straightens” by cutting through a meander

cutbanks

the side of a meandering river where the water moves the fastest and greatest erosion occurs

point bar

depositional feature located on the inside curve of a meandering river where flow slows and increased deposition occurs

pothole

rivers can dig a pothole in the sediments at the bottom of the river (think “blender”)

river landforms

floodplains

created when rivers overflow (seasonally) leaving behind rich alluvial (clay, silt, sand, gravel) deposits

levees

natural banks created by the deposition of sediment (flooding), they can act as a natural protectant against floods

dike

person-made levee

delta

build up of sediments at the mouth of a river where it deposits more material than can be carried away

• arcuate (fan-shaped) delta

• bird’s foot delta

• estuarine delta

types of waves

spilling (constructive) waves

• flat, low in height and have a long wavelength

• their swash carries material up beach

• the wave energy gets weaker as it returns to the ocean (backwash)

• builds up the beach

plunging (destructive) waves

• large wave height but short wavelength

• high downward forces and strong backwash

• the high downward energy helps erode beach material

• occurs at cliffs as well as beaches

longshore drift

• waves normally approach the shore on an angle

• sand is driven up-beach by the power of incoming waves and is transported along the beach in a horizontal motion

• longshore drift = zig-zag movement of sand along the beach

erosional features of waves

• with cliffs, hydraulic action opens up a crack

• crack grows into a cave through abrasion and hydraulic action

• cave breaks through the headland and forms an arch

• arch is eroded and collapses, forming a stack

spit

• sand, silt and clay from eroded coastlines are slowly carried by longshore drift and ocean currents

• forms a protruding feature off the coast

tombolo

• natural pathway that joins an island to the mainland

stack

• isolated pillar left behind when an arch collapses

glacier

• a long-lasting body of ice (decades or more) that is large enough to move under its own weight

  • can advance, stay stationary, and retreat

glacier formation

• glaciers need 2 things to form:

  • prolonged cold

  • an accumulation of snow

types of glaciers

alpine (valley) glacier

• higher altitude

• follow the river valleys as they move from the mountains to the lowland areas

• often join with other alpine glaciers to create massive valley glaciers.

continental glacier

• higher latitude

• when valley glaciers are no longer confined to river valleys, they spread out to large ice sheets

• can be more than a kilometer thick

• move very slowly

• when they retreat, they leave behind rich deposits of soil, and many lakes across the prairies

snow layers

• new snow (snowflakes)

• old snow

• firn (crunchy ice crystals)

• glacial ice

moraines

sediment left behind by glaciers