I ghiacciai e lopera del ghiaccio Cap. 16 Press et al., Capire
la Terra Cap. 31 Strahler, Geografia fisica
Slide 2
Press et al., Capire la Terra I ghiacciai Da neve a ghiaccio
Gli strati nevosi, soggetti a processi di costipamento
costituiscono il nevato.
Slide 3
Lupia Palmieri, Parotto, Osservare e capire la Terra Zanichelli
editore 2010 I ghiacciai Limite delle nevi permanenti
Slide 4
BILANCIO DI MASSA GLACIALE Lablazione pu avvenire per:
1)Fusione 2)Calving 3)Sublimazione 4)Erosione eolica
Slide 5
15.1 Taku and Norris Glaciers, Juneau Icefield, Alaska (Aerial)
Photograph by Peter L. Kresan The advancing terminus of the Taku
Glacier (upper center) and the retreating terminus of the Norris
Glacier (bottom) are shown in this aerial view. The convex profile
of the terminus and lack of a trimline along the margins of the
Taku Glacier are indicative of an advancing glacier. In fact, the
glacier is plowing down forest on both sides of this advancing
lobe. The concave profile of the terminus, the clearly visible
trimline, and proglacial lake of the Norris Glacier are
characteristic of a retreating glacier. A trim line, also written
as trimline, is a clear line on the side of a valley formed by a
glacier. The line marks the most recent highest extent of the
glacier. The line may be visible due to changes in color to the
rock or to changes in vegetation on either side of the
line.glacier
Slide 6
15.10 Athabasca Glacier, Columbia Icefield, Canada Photograph
by Peter L. Kresan The terminus of the Athabasca Glacier in 1985
can be compared to its position, marked by the monument, in 1975.
Since 1945, the glacier has retreated 2950 ft (900 m). Total
recession of the ice front from 1870 to 1881 is approximately 1 mi
(1.6 km), about 50 ft (15 m) per year. The Athabasca Glacier is 3.7
mi (6 km) long. Meltwater from the glacier flows into the Sunwapta
and Athabasca rivers and eventually into the Arctic Ocean via the
Mackenzie River.
Slide 7
Ghiacciai vallivi e calotte glaciali
Slide 8
Lupia Palmieri, Parotto, Osservare e capire la Terra Zanichelli
editore 2010 I ghiacciai vallivi I ghiacciai vallivi, o alpini, si
originano ad elevate altitudini e defluiscono lungo valli scavate
nelle rocce in posto
Slide 9
I ghiacciai vallivi: morfologia
Slide 10
Strahler, Geografia fisica. Ed. Piccin
Slide 11
15.18 Taku Glacier Terminus, Taku Inlet, Juneau, Alaska
(aerial) Photograph by Peter L. Kresan This aerial view (taken in
the summer) shows the advancing terminus of the Taku Glacier as it
enters Taku inlet near Juneau, Alaska. The convex (bulging) profile
of the terminus and lack of a trimline along the margins of the
Taku Glacier are indicative of an advancing glacier. In fact, the
glacier is plowing down forest on both sides of this advancing
lobe. In the distance, where the glacier bends to the left, the
surface of the glacier becomes lighter and smoother as the rough,
crevassed surface becomes covered with snow. This change in the
surface of the glacier marks the snowline, above which snowfall
from the previous winter does not melt entirely. Largest in the
Juneau Icefield of southeastern Alaska, the Taku Glacier is a
temperate, maritime glacier. It has advanced more than 6.8
kilometers since 1890 and 1.6 kilometers since 1948. Studies by the
Juneau Icefields Research Program show that the Taku Glacier has a
positive mass balance of +0.37 meter per year for the period
1946-1986. This positive accumulation of snow on the glacier
accounts for its growth through the end of the 20th Century, even
though many other glaciers have been retreating (Pelto &
Miller, 1990).
Slide 12
Forme superficiali La superficie del ghiacciaio si comporta
come un corpo rigido, i movimenti differenziali dei vari strati che
lo compongono determinano la frantumazione del ghiaccio in blocchi
dando origine ai crepacci, che spesso si incrociano isolando
blocchi e formando profonde fenditure, i seracchi.
Slide 13
Movimento di un ghiacciaio vallivo
Slide 14
Slide 15
15.12 North Pole, Arctic Ocean Photograph by Yar Petryszyn
Yamal, a Russian nuclear icebreaker, makes it to the North Pole,
Arctic Ocean, in July. 15.13 North Pole, Arctic Ocean Photograph by
Yar Petryszyn A break in sea ice at the North Pole exposes open
water in the Arctic Ocean. I ghiacciai continentali o
inlandsis
Slide 16
15.14 Flow of Sea Ice in Arctic Ocean Photograph by Yar
Petryszyn Flow of sea ice in Arctic Ocean mimics the movement of
Earth's crustal plates. Note the oblique spreading centers
connected by transpressional transform faults.
Slide 17
15.15 Mount Munson, Antarctic Photograph by Paul Fitzgerald
View east-northeast across the Queen Maud Mountains from Mount
Munson, Antarctica. Mount Munson, Antarctic
Slide 18
Movimento di un ghiacciaio continentale
Slide 19
Prima della glaciazione: Rilievi dalle forme morbide, valli a V
In cosa si differenziano le valli glaciali dalle valli fluviali?
Durante la glaciazione: Ghiacciai tributari e valle glaciale
principale
Slide 20
Quando il ghiaccio scompareemergono rilievi dalle forme aspre,
circhi, valli sospese con cascate, valli a U Anche i ghiacciai
tributari scavano dei truogoli ad U, ma questi hanno una sezione
trasversale di ampiezza pi ridotta ed il loro fondo situato pi in
alto rispetto a quello delle valli principali, per cui sono
chiamati truogoli sospesi.
Slide 21
Le valli glaciali sono tipicamente a U poich il ghiaccio erode
sia il fondovalle che i versanti. Esse hanno un profilo ondulato
perch il ghiacciaio tende ad accentuare le irregolarit. Spesso le
valli fluviali si sovrappongono, al ritiro del ghiaccio, alle
preesistenti valli glaciali. Dove due o pi ghiacciai confluiscono
si possono formare valli sospese.
Slide 22
15.21 Glacial Carved Valley of Glen Coe, Scotland Photograph by
Peter L. Kresan This is a view to the west up Glen Coe, a classic
example of a U-shaped valley. In the foreground is a glacial
polished surface of 380 million year old andesitic volcanic rock.
About 3 million years ago a deterioration of climate led to the
build up of glaciers and ice sheets in Scotland. The last
glaciation began about 27,000 years ago, reached its maximum about
18,000 years ago, and melted away by about 10,000 years ago,
leaving this landscape.
Slide 23
15.4 Half Dome and Tenaya Canyon, Yosemite, California
Photograph by Peter L. Kresan From Glacier Point in Yosemite, one
can easily imagine Tenaya Canyon partially filled with ice 15,000
years ago, just like the Great Gorge in Alaska is today (see Slide
15.3). Immediately to the left of this view, Tenaya and other
canyons join to form Yosemite Valley. The U-shape profile of Tenaya
Canyon is characteristic of glacial carved valleys. Till and
outwash deposits level out the floor of the valley.
Slide 24
15.3 The Great Gorge, Ruth Glacier, Alaska Range (Aerial)
Photograph by Peter L. Kresan About 15 mi up the Ruth Glacier from
the location shown in Slide 15.2 is the Great Gorge. This is a
wonderful analog to what Tenaya Canyon and Yosemite Valley must
have looked like during the last ice age (see Slide 15.4). Work
reported in Earth magazine (March 1993) indicates that the Great
Gorge is the deepest gorge in North America-3800 ft (1160 m) deep.
The vertical relief from the top of Mt. Dickey (upper right) to the
bedrock floor of the gorge is 9000 ft (2740 m).
Slide 25
Levoluzione di una valle glaciale Il ghiaccio ha una densit
tale che, quando galleggia, da 3/4 a 9/10 della sua massa si
trovano sotto il livello del mare. Quindi, un ghiacciaio pu erodere
ben sotto il livello del mare!
Slide 26
15.22 Sognefjord near Aurland, Norway Photograph by Peter L.
Kresan This is a view of the Aurland arm of the Sognefjord, the
worlds longest fjord, in the heart of Fjordland, southwestern
Norway. Glaciers retreated from this region about 9,000 to 10,000
years ago, leaving a dramatic landscape of fjords, waterfalls, and
rounded mountain tops and plateaus. Fjords typically mark the
location of faults or fracture systems in the bedrock. Fjords open
to the ocean. Their dimensions are difficult to imagine. Glacial
sediments and water partially fill the fjord to depths of hundreds
of meters. One section of the Sogne Fjord has sides that tower
1,220 meters above the water level and extend another 1,220 meters
below. To reach open ocean from the location of this image, you
would travel close to 200 kilometers in a jet boat.
Slide 27
15.9 McCarty Ford, Kenai Peninsula, Alaska (Aerial) Photograph
by Peter L. Kresan The Harding Icefield on the Kenai Peninsula of
Alaska feeds the McCarty Tidewater Glacier, which cut this 23-mi
(37-km) -long fjord. Since 1860, the McCarty Glacier has retreated
17 mi (27 km) to its present position at the head of the fjord.
Most tidewater glaciers in Alaska have undergone rapid retreat
during the twentieth century.
Slide 28
Azione geomorfologica: forme di erosione I ghiacciai esercitano
unazione erosiva potente ed efficace sulle rocce del fondo e sui
versanti. Essa si esplica attraverso due processi: La rimozione dei
frammenti gi disgregati Lestrazione di detriti dai versanti e dal
fondo. I detriti sono trasportati nella massa di ghiaccio o sulla
sua superficie. Lazione erosiva sul fondo detta esarazione. Le
rocce vengono levigate e striate solo sul lato rivolto verso monte,
sono cos asimmetriche e vengono dette rocce montonate.
Slide 29
15.7 Glacial Striations and Polish, Athabasca Glacier, Columbia
Icefield, Canada Photograph by Peter L. Kresan Glacier-striated and
-polished bedrock is exposed beneath a mantle of till at the
terminus of the Athabasca Glacier in the Rocky Mountains, Canada.
This photo was taken on top of a bedrock hill, probably a roche
moutonn, that has just become exposed as the glacier retreats (see
Slide 15.10).
Slide 30
15.20 Exposed Bedrock along the Flank of the Mendenhall
Glacier, Juneau, Alaska Photograph by Peter L. Kresan This exposure
of ice-polished bedrock near the terminus of the Mendenhall Glacier
is within a trimline which parallels the glaciers flank. The
trimline is barren of vegetation and exposes bedrock and glacial
till. A trimline forms during a period of recent glacial ice
retreat. Over a period of decades, the trimline will become
progressively more obscure as vegetation expands into this
disturbed area. So in contrast to the Taku Glacier, the Mendenhall
is retreating. Additional evidence for its retreat is found beyond
the glacial terminus behind the person in the upper right, where
thirteen distinct recessional moraines mark different stages of the
retreat. In 1750, during the Little Ice Age, the Mendenhall Glacier
extended 4 kilometers farther down the valley.
Slide 31
15.6 Glacial Erratic, South Bubble, Acadia, Maine Photograph by
Peter L. Kresan The speckled white color of this glacial erratic
does not match the pink granitic rock of the South Bubble in Acadia
National Park, near Bar Harbor, Maine. The closest outcrop of
bedrock matching the boulder is many miles to the north. Massi
erratici
Slide 32
Forme di deposito
Slide 33
15.2 Ruth Glacier, Alaska Range (Aerial) Photograph by Peter L.
Kresan This low aerial oblique view down the Ruth Glacier in Alaska
shows medial and lateral moraines. The Ruth Glacier is a valley or
piedmont glacier formed by the confluence of many smaller
glaciers.
Slide 34
15.19 Lateral Moraine, Tasman Glacier, Mount Cook National
Park, New Zealand Photograph by Peter L. Kresan This long lateral
moraine along the west flank of the Tasman Glacier was formed when
the glacier was much thicker during its last advance. Starting in
the 1890s, the ice began its retreat and the rock debris, plastered
along the mountain flank, collapsed to form this ridge.
Slide 35
Slide 36
Lupia Palmieri, Parotto, Saraceni, Strumia, Scienze integrate
Zanichelli editore 2010 I cambiamenti climatici La temperatura
atmosferica media annua degli ultimi 750 000 anni variata da
condizioni di clima pi freddo (periodi glaciali) a condizioni di
clima pi caldo (periodi interglaciali)
Slide 37
Lupia Palmieri, Parotto, Saraceni, Strumia, Scienze integrate
Zanichelli editore 2010 I cambiamenti climatici Landamento della
concentrazione di anidride carbonica nellatmosfera da 650 000 anni
fa a oggi
Slide 38
15.16 Ice Lab at the Department of Geosciences, University of
Arizona Photograph by Peter L. Kresan Sublimation of a
100,000-year-old Vostok ice core from Antarctica in the Ice Lab at
the Department of Geosciences, University of Arizona. Trapped gases
within the ice, such as carbon dioxide, are collected and studied
to reconstruct past levels of the gases in Earth's atmosphere.
15.17 Lemon Glacier, Juneau Icefield, Alaska Photograph by Peter L.
Kresan Snow accumulation study on the Lemon Glacier, Juneau
Icefield, Alaska. The thin bluish ice layers mark past summers'
melt surfaces.
Slide 39
Lupia Palmieri, Parotto, Saraceni, Strumia, Scienze integrate
Zanichelli editore 2010 I cambiamenti climatici Le due fotografie,
scattate dallo stesso punto di osservazione nel 1910 e nel 2001,
mostrano di quanto si ridotto il Ghiacciaio di Tschierva, nelle
Alpi svizzere
Slide 40
Variazioni rapporto isotopico O 16 /O 18 18 O is two neutrons
heavier than 16 O and causes the water molecule in which it occurs
to be heavier by that amount. The addition of more energy is
required to vaporize H 2 18 O than H 2 16 O, and H 2 18 O liberates
more energy when it condenses. In addition, H 2 16 O tends to
diffuse more rapidly.neutronsvaporizecondenses The 18 O/ 16 O ratio
provides a record of ancient water temperature. Water 10 to 15
degrees Celsius (18 to 27 degrees Fahrenheit) cooler than present
represents glaciation. Precipitation and therefore glacial ice
contain water with a low 18 O content. Since large amounts of 16 O
water are being stored as glacial ice, the 18 O content of oceanic
water is high. Water up to 5 degrees Celsius (9 F) warmer than
today represents an interglacial, when the 18 O content of oceanic
water is lower. A plot of ancient water temperature over time
indicates that climate has varied cyclically, with large cycles and
harmonics, or smaller cycles, superimposed on the large ones. This
technique has been especially valuable for identifying glacial
maxima and minima in the Pleistocene.degrees Celsiusdegrees
FahrenheitglaciationharmonicsPleistocene
Slide 41
Slide 42
Slide 43
Slide 44
Slide 45
Slide 46
Glaciazioni europee Modello riferibile al versante
settentrionale delle Alpi Pleistocene inferiore interglaciazione
Donau-Gnz (1.700.000-1.200.000 anni fa) glaciazione Gnzglaciazione
Gnz (1.200.000-700.000 anni fa) Pleistocene medio interglaciazione
Gnz-Mindel (700.000-650.000 anni fa) glaciazione Mindel
(650.000-300.000 anni fa)Mindel interglaciazione Mindel-Riss
(300.000-250.000 anni fa) glaciazione Riss (250.000-120.000 anni
fa)Riss Pleistocene superiore interglaciazione
Riss-Wrminterglaciazione Riss-Wrm (120.000 - 80.000 anni fa)
glaciazione Wrmglaciazione Wrm (80.000-10.000 anni fa)