streams, glaciers and NE history

taconic orogeny (450 Ma)

ordovician period, collision between ancient north america and gander microcontinent

acadian orogeny (400 Ma)

devonian, collision of NA + gander with avalon

alleghanian orogeny (300 Ma)

mississipian - permian, formation of Pangea through the collision of NA with africa and europe

North america 500 Ma in cambrian times

NH was a shallow marine environment, near the equator, evidence from fossil reefs in limestone, edge of North America was a convergent margin

taconic orogeny rock formations

as the ocean basin closed and continents collided huge mountain belts were formed generating thrust faults (Champlain VT), lebanon granite formed, tuff, ammonusic volcanics

gile mountain formation (acadian orogeny)

420 Ma, mud and sand deposited in kronos ocean basin, buried and metamorphosed into phyllite (was prev schist and quartzite)

NE in 200 Ma / jurassic period

NH begins to pull away from VT, failed rifting, beginning of the mid atlantic ridge

granite intruded

watershed

region that precipitation drains into, varies due to climate, geology, land uses, vegetation

stream formation

precipitation concentrates in local low point, ground water fills pores in soil, water table intersects surface

easier to form when bedrock is close, land in steep or wet envr

tributaries and confluence

tributaries are streams that join the main stem at the confluence

stream discharge

measure of how much water flows through a channel.

cross-sectional area x velocity

measured by stream gauging sys or a rating curve/hydrograph

stream power

rate of energy dissipation against the bed per unit of downstream length

density x acceleration x discharge x slope

stream sediment loads

dissolved: material carried in solution by the stream aka ions

suspended: carried by water column that is too fine to settle in most follow envr

bed load: large sediments, rolling or saltating

incision/down cutting

erosion, or removal of material from earth’s surface

base level

the level below which a stream cannot downcut, ocean or local base levels

changes to base level

increased sea level and crustal uplift increases base level

raised base level leads to increase sediment deposition forming allviums

lowered base level leads to erosion and a river terrace

cut bank

outside curve preferentially eroded and deepened

point bar

sediments deposited on the inside of the curve where velocity is low

glacier

mass of snow/ice that lasts year round and deforms under its own weight, types include valley, cirque and marine terminating

antartica

ice shelves extend into ocean, important for stability, west Antarctica is below sea level

importance of glaciers

respond and drive climate change, storage of freshwater, records past atmosphere in gas bubbles

freshwater storage and est. sea level rise

ice caps + small glaciers 0.5m

greenland 6-7km

east ant. 64km

west 8km

total 80km

sea level rise today

mainly from thermal expansion (h20 molecules are further apart

accumulation

adds mass to the glacier, through precipitation

ablation

area where mass is loss, due to sublimation (transpiration from solid ice to water vapor), ice berg calving

mass balance/equilibrium line

difference between accumulation and ablation

glacial flow

flows in direction of top surface, driving force is a result of thickness and surface slope

ice sheets spread laterally

plastic/internal deformation

behaves like metamorphic rock, grains flatten in direction of stress, occurs at depth due to pressure

basal sliding

water saturated sediment lubricates the bottom of the glacier which moves across it, extremely erosive

brittle deformation

occurs at the surface, forms crevasses

types of glacial erosion

plucking, plowing, scouring

glacial sediments

unsorted: till, sorted: glacial lake deposits (varves)

glacial retreat

occurs when melting out pases downward movement

moulin

waterfall like flow of glacial melt water, surface melting speeds movement of glacier and melting

ice shelves

extended far into the ocean, grounded by grounding line/sea floor, provides shelf stability and has a buttressing effect

warmer water can circulate below causing melting

Laurentide ice sheet

20,000 years ago, extended to LI and cape cod

900 - 3300m thick

drumlin

oval or elongated hill (football-shaped) formed by the streamline movement of glacial ice, composed of till, found in broad low land regions, axis parallel to ice flow direction

Moraine

ridges made of glacial till (ranging from boulders to silt) typically at the glaciers edge; types include medial, lateral and end moraines 

• Glacial moraines deposited by the laurentide ice sheet can be observed through NY and MA tracing the glacier’s path of retreat

Outwash

sediment that is carried and deposited by meltwater, sorted and layered due to water

Esker

an elongated ridge of sediments formed in a sub-glacial meltwater tunnel, as the ice moves away, sediment accumulates

Kettle pond

a depression formed in glacial sediments by a block of calved ice (which is buried by sediments)

Pro-glacial lake

lake that forms in front of a glacier or ice sheet, composed of meltwater 

Glacial varves

deposited by pro-glacial lakes, annual sediment layers formed by the deposition of sediments influenced by seasonal patterns

• sand/silt deposited in the summer (coarser, lighter)

• Clay deposited during the winter (finer, darker)

• The first varve and the bedrock can help track time of deglaciation 

• Varve thickness is influenced by proximity to the glacier, closer varves are thicker and farther away ones are thinner, differences in precipitation 

• Original materials perserved within varve layers are radio carbon dated to identity time of formation

Ice-sheet recession

• Time of deglaciation from varves deposition on till, gravel or bedrock

• Very thick basal varves indicate ice-proximal environments 

• Long island moraines deposited 23,000 years ago

• Ice began to move up the CT river valley about 19,000 years ago 

• Hanover deglaciated at 14,000 years ago 

• Varves show it took nearly 6,000 years for the ice sheet to move from NY to Hanover, varves progressively younger northward

aggregation

deposition of sediments