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Glacial legacies new
 

Glacial legacies new

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    Glacial legacies new Glacial legacies new Presentation Transcript

    • At least 4 geologically recent ice ages glaciers covered almost all the land surfacNew York State and Vermont. This is probably what most of the state looked likeits peak about 20,000 years ago.2
    • 3GlacierGlacier::•• A mass of ice and surficial snowA mass of ice and surficial snowthat persists throughout the year andthat persists throughout the year andflows outward or downhill like a fluidflows outward or downhill like a fluidunder its own weight. Most range inunder its own weight. Most range insize from 100 meters to 10,000size from 100 meters to 10,000kilometers.kilometers.Two types of glaciers:Two types of glaciers:• AlpineAlpine (form in mountains/valleys)(form in mountains/valleys)• ContinentalContinental (exist at the poles, advance(exist at the poles, advancecovering continents)covering continents)
    • 6The average global temperatures over the past 1000,000 years (see below).There have been 5 Ice Ages throughout earth’s history.The last continental glacier was called the “Wisconsin Ice Sheet.”6
    • What causes Ice Ages?• Milankovitch Theory: small, regularchanges in the earth’s orbit and in the tiltof earth’s axis cause Ice Ages.» Shape of earth’s orbit changes every 100,000thousand years. Elliptical to circular and back» Tilt of earth’s orbit: (21.5 to 24.5 degrees)» Precession: circular movement of earth’s axis.• Other: irregularities of the sun, volcanicdust, or position of the continents.
    • 8Ice coverage of North America approximately 21,000 years ago
    • 99The only part of New York that wasclearly never covered by glaciers isAllegheny State Park in Western NewYork State.Long Islandwas built byglacialsediment.
    • Evidence of Glaciers in VT• Rounded mountain tops (abrasion)• Roche moutonnée topography (Camels Hump is aclassic and well-known example, with a sloping northface and very steep south face)• Lake Winooski and Lake Hitchcock (CT River)• Eskers• U-shaped valleys• Champlain Sea and the Charlotte Whale• Gravel and sand deposits along Lake Champlain• Striations and erratics• Glacial and Fjord-type lakes (Crystal Lake, LakeWilloughby)
    • 11The alpine Athabaska Glacier in Alberta, Canada is one ofthe most accessible modern glaciers. Note the road andcars parked left of the melt water lake.Which type of glacier is this?
    • 12Glaciers push, drag and carry great quantities ofsediment from clay size to boulders. The blue linesshow the far edge of this glacier about a quarter mileaway.This is the Castner Glacier in Alaska.1212
    • Two lateral (side) moraines beside the Athabaska glacier. Iceflowing in the valley to the right has pushed these ridges ofunsorted till into place.1313
    • 14Debris from the continental glaciers was left behind asirregular terrain such as this terminal (end) moraine on CapeCod. 14
    • 15Locations of moraine deposits in New YorkState
    • Glacial till sediment, insome places hundredsof feet thick, coversmost of New YorkState.What can we say aboutthe “sorting” of glacialtill?16
    • Within moraines closed depressions are common. Some may have been createdby a block of ice melting within the glacial deposits. Here we see ice on a formerwater surface. The ice makes this kettle northwest of Oneonta especially visible.17
    • Terminal moraines form the backbone of Long Island and extend to the east.18
    • 19The Ronkokoma Moraine dips below sea level atMontauk Point. This is New York’s most easternlandfall. Note the boulders washed out of themoraine.19
    • This hummocky, irregular land surface south of Naples, NYis a part of the Valley Heads Moraine. The irregular landsurface and kettle holes are typical of moraines.20
    • 21Sedimentdepositeddirectly by theice Is a mixedjumble ofsediment fromclay sizeparticles tolarge boulders.But this islayered glacialoutwash onLong Island thatis deposited bywater from themelting glaciers.Layeringindicates waterdeposits while ajumble ofunsortedmaterial is asign of glacialice deposits.
    • The north shore of Long Island has bluffs of glacial till in the HarborHill Moraine. The transported rocks of diverse types settle onto thebeach.2222
    • Glacial outwashdeposits are a primesource for high qualitysand and gravel.Surprisingly. this isNew York State’s mosteconomically valuablegeological resource.23
    • The ice wall is thelower end of theCastner Glacier incentral Alaska.Glacial meltwaterfeeds this fastflowing riveremerging from theglacier. Much ofthe melting occursat the bottom ofthe ice.Long ridges calledeskers aresometimesdeposited intunnels by thesesubglacialstreams.24
    • An esker is along US Route 6 in Northern Westchester County, NY.25
    • Another esker follows NY Route 79 north of Binghamton, NY.26
    • 27Parts of Route 79 were built right along the esker. (See the arrows.)Eskers make a firm road base, that is well drained and can supply hgh qualitysand and gravel.
    • Glacial depositssuch as these atCroton Point in theLower Hudson Rivercontain rocks thathave beentransported by themoving ice.Although most ofNew York State doesnot have igneous ormetamorphicbedrock, these rocktypes are commonthroughout the statein glacial deposits.28
    • Cobblestone homesin Western New YorkState wereconstructed fromglacially depositedstones that wereembedded in thickmortar.Many of these stonesdiffer greatly from thecomposition ofnearby bedrock.Some of them wereclearly transportedhundreds of milessouthward fromCanada.29
    • An erratic is an especially large transported rock. This one is almost thesize of a house. It is located east of Tarrytown, NY.3030
    • Occasionally an erratic is left perched on top of smaller bouldersafter many years of erosion. This perched erratic is at North Salemin Westchester County.31
    • Drumlins are elongated hills of unsorted sediment, usually aligned north-south. Drumlinsform under continental glaciers. Hundreds of them can be seen between Rochester andSyracuse in Western New York State.32
    • This is pat of drumlinfield east ofRochester, NY. Notethat the trailing endsof the hills are thesouthern slopes. Thenorth slopes areusually more blunt.33
    • New York’s drumlin field is among the most extensive anywhere.34
    • Drumlins are eroded by waveaction along the south shore ofLake Ontario at Chimney BluffsCounty Park.Fine clay binds the sediment theincludes particles as big as largeboulders. The unsorted sedimentis an indication of ice depositedtill.Mr. Coyle grew up half a mile fromhere, this is where he swam as alittle kid!35
    • 36Both alpine and continental glaciers scour broad U-shaped valleys. This is about a ten mile walk up the thealpine Castner Glacier.36
    • 37A V-shaped stream valley suchas this in the Rocky Mountainsof Colorado is the work ofstream erosion.
    • Some New York streams, includingthe Genesee River in LetchworthGorge carve out narrow V-shapedvalleys.38
    • Glaciers carved this broad U-shaped valley in the Rocky Mountains of Montana.39
    • U-shaped valleys such as this one inthe western Finger Lakes arecommon in this part of New YorkState.4040
    • The Finger Lakes of Western New York State were excavated as U-shaped valleys by the glaciers advancing to the south. Morainesdammed the former south flowing outlet rivers.4141
    • Portions of Seneca and Cayuga Lakes looking north froman airplane. Can you match them with the last image?42
    • Looking north along Canandaigua Lake in the Finger Lakes.43
    • 44Glacial erosion deepened the main north-south valley where the town of Montour Falls,NY is located. But the east-west tributary valleys were not made deeper. So thiswaterfall descend from a hanging valley.
    • Glacial polish and striations (diagonal to the top left) aredisplayed on this rock surface near Tarrytown.45
    • 46Striations can beobserved at about4000 feet elevationon Hunter Mountainin the Catskills.They show that theice was a minimumof a mile thick overthis part of NewYork State.
    • 47Grooves and glacial polish near Peekskill, NY document the southwardmovement of the ice. Also notice the stepped edges on the right (south)side.47
    • 48Glacially carvedgrooves are common inthe hard rocks of theAdirondacks.48
    • Rocks carried by a glacier are often partiallyrounded and scratched by abrasion withother rocks.49
    • Chatter marks and crescent gouges on hard bedrock surfacesare more evidence of glacial movement.505050
    • 51A whaleback (or roche mountonnée) is a bedrock surface that has beenscoured on the north side and plucked on the south end. They are commonin areas of hard crystalline bedrock.51
    • 52From this image it’s clear that the ice moved southward from left to right toproduce whalebacks in Canopus Lake, Putnam County, NY.52
    • 53The Hudson River Valley from Cornwall to Peekskill is the only glacially carvedfjord on the east coast of North America. Ocean vessels can travel all the way upto Federal Dam north of Albany.53
    • The angular and jagged landscapes of theSouthwest such as at Monument Valley in Arizona,indicate an area that was never covered bycontinental glaciers.54
    • But even thehighest of theAdirondackMountains haverounded summitseroded by theglaciers.5555
    • A kame is a hill that has been deposited like a delta at the edgeof a glacier. This kame is in a town park in Shortsville, NY, nearRochester.56
    • 57How selected features of continental glaciation, including kames, originated.
    • Retreat (melt back) of the glaciers with successive melt water lakes and rivers.58
    • 59One of the melt water channels created a waterfall morepowerful than Niagara Falls that fell over these cliffs at ClarkReservation in Syracuse. As you see, the waterfall is now dryexcept for the plunge pool at the bottom.
    • At Croton Point in the Lower Hudson Valley, till with unsortedsediment can be seen. Below the till are fine grained freshwater lake deposits with annual layers. These are known asvarves. Clay varves document the age of post-glacial LakeAlbany.6060
    • 61The courses of both the Niagara River and the Genesee River were changed causingthem to make dramatic new gorges and waterfalls.
    • The weight of theglaciers caused partof North America tosink.Since the ice hasmelted, rebound iscausing thesedepressed areas toslowly rise to theirpre-glacialelevations.Note Hudson Bay,which lies over adepressed part ofEarth’s graniticcontinental crust.62
    • 63One result of postglacial isostatic rebound is these bays along the south shoreof Lake Ontario. The north shore has rebounded more than the south shore,causing the lake to invade stream valleys. Sodus Bay is a good example.Lake Ontario
    • 64Note the baymouth bar built by Lake Ontario waves andcurrents across the entrance to Sodus Bay nearRochester, NY.64
    • Pattern GroundPattern ground is rock pushed into polygons by the freeze-thaw cycles in apost-glacial climate. This image is a location in the Rocky Mountains, butsimilar patterned ground can be observed in some Catskill forest locations.6565
    • Finger LakesDrumlin FieldLong IslandMorainesPolish,GroovesStriationsMajor regional features of the iceages.Valley Heads MoraineRoundedMountainTopsPost-glacial Lakes66Eskers,KamesTillbanksChangedstreamchannels
    • The end.(…or is a new ice age right around thecorner?)67
    • Locations of theimages by slidenumber and New Yorkparks (P) that highlightglacial forms.P68PP1314161718181920222526282930313234353840434445464748505351 5255566064PP P61 PPPPP PPP2159