Deglaciation dynamics following the Little Ice Age on Svalbard:
Deglaciation dynamics following the Little Ice Age on Svalbard:
Deglaciation dynamics following the Little Ice Age on Svalbard:
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Søren H. Rasmussen<br />
“moraine-mound complex”. Unlike <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
landsystem model Larsbreen’s and<br />
Platåbreen’s moraine-mound complex is<br />
ice-cored with glacier ice. The “inner<br />
z<strong>on</strong>e” is not exciting because <str<strong>on</strong>g>the</str<strong>on</strong>g> glacier<br />
ice c<strong>on</strong>tinues under <str<strong>on</strong>g>the</str<strong>on</strong>g> moraine-mound<br />
complex.<br />
In <str<strong>on</strong>g>the</str<strong>on</strong>g> landsystem model glacier ice<br />
from <str<strong>on</strong>g>the</str<strong>on</strong>g> outer moraine ridge to <str<strong>on</strong>g>the</str<strong>on</strong>g> present<br />
glacier terminus is melted or left as deadice.<br />
On Larsbreen and Platåbreen debris<br />
cover are preventing <str<strong>on</strong>g>the</str<strong>on</strong>g> glacier ice for<br />
melting.<br />
In <str<strong>on</strong>g>the</str<strong>on</strong>g> text of Glasser and Hambrey<br />
(2006) where <str<strong>on</strong>g>the</str<strong>on</strong>g> landsystem model is<br />
presented it is not clear witch glacier it is<br />
building <strong>on</strong>. In <str<strong>on</strong>g>the</str<strong>on</strong>g> text <str<strong>on</strong>g>the</str<strong>on</strong>g>re are menti<strong>on</strong><br />
glacier from twelve locati<strong>on</strong>s, see figure 9.<br />
If <str<strong>on</strong>g>the</str<strong>on</strong>g> model is made <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> base of <str<strong>on</strong>g>the</str<strong>on</strong>g>se<br />
glaciers <str<strong>on</strong>g>the</str<strong>on</strong>g>re can be a problem with <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
representati<strong>on</strong>. Only <strong>on</strong>e of <str<strong>on</strong>g>the</str<strong>on</strong>g> twelve<br />
locati<strong>on</strong>s are in tertiary bed rock, see figure<br />
9. O<str<strong>on</strong>g>the</str<strong>on</strong>g>r glaciers are located in harder bed<br />
rock, e.g. tree in <str<strong>on</strong>g>the</str<strong>on</strong>g> metamorphic Hecla<br />
Hoek. A harder basement could release<br />
debris slower than <str<strong>on</strong>g>the</str<strong>on</strong>g> softer rock <str<strong>on</strong>g>the</str<strong>on</strong>g>reby<br />
leaving less sediment to build up a debris<br />
cover. The c<strong>on</strong>sequent of this is debriscovered<br />
glacier are not <str<strong>on</strong>g>the</str<strong>on</strong>g> typical <strong>Svalbard</strong><br />
glacier or <str<strong>on</strong>g>the</str<strong>on</strong>g> model is based <strong>on</strong> n<strong>on</strong><br />
representative glacier.<br />
Glaciofluvial processes<br />
The areas <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> moraines where <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
biggest amplitude in <str<strong>on</strong>g>the</str<strong>on</strong>g> relief is observed<br />
are in associati<strong>on</strong> with meltwater channels.<br />
On Larsbreen this is al<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g> main surface<br />
meltwater channel in <str<strong>on</strong>g>the</str<strong>on</strong>g> middle of <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
fr<strong>on</strong>tal moraine, see figure 5. Platåbreen<br />
has two main meltwater channels <strong>on</strong>e in<br />
each side of <str<strong>on</strong>g>the</str<strong>on</strong>g> fr<strong>on</strong>tal moraine, see figure<br />
3. Especially <strong>on</strong> Larsbreen debris-flow is<br />
c<strong>on</strong>centrated down towards <str<strong>on</strong>g>the</str<strong>on</strong>g> main<br />
channel.<br />
In areas between two near channels are<br />
usually a ridge. This is seen at <str<strong>on</strong>g>the</str<strong>on</strong>g> eastern<br />
lateral moraine of Larsbreen, western side<br />
of Larsbreen fr<strong>on</strong>tal moraine and al<strong>on</strong>g <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
<str<strong>on</strong>g>Deglaciati<strong>on</strong></str<strong>on</strong>g> <str<strong>on</strong>g>dynamics</str<strong>on</strong>g> <str<strong>on</strong>g>following</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> <str<strong>on</strong>g>Little</str<strong>on</strong>g> <str<strong>on</strong>g>Ice</str<strong>on</strong>g> <str<strong>on</strong>g>Age</str<strong>on</strong>g> <strong>on</strong> <strong>Svalbard</strong>:<br />
Implicati<strong>on</strong> of debris-covered glaciers dynamic and morphological setting<br />
Page 11 of 15<br />
western lateral moraine of Platåbreen.<br />
These slopes are often steep towards <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
channels, suggesting that <str<strong>on</strong>g>the</str<strong>on</strong>g> debris is<br />
transported to <str<strong>on</strong>g>the</str<strong>on</strong>g> channels. This will be<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> main transport of sediments away from<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> glacier forefield.<br />
Rock-glaciers at Larsbreen <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
eastern side and wea<str<strong>on</strong>g>the</str<strong>on</strong>g>ring material <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
bedrock <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> western side allow water,<br />
and <str<strong>on</strong>g>the</str<strong>on</strong>g>reby sediments, to escape <strong>on</strong>ly<br />
through <str<strong>on</strong>g>the</str<strong>on</strong>g> middle nor<str<strong>on</strong>g>the</str<strong>on</strong>g>rn channel outlet,<br />
<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> surface or through <str<strong>on</strong>g>the</str<strong>on</strong>g> tunnel, of <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
fr<strong>on</strong>tal moraine.<br />
Platåbreen has today two patches for<br />
transporting water to lower laying area,<br />
<strong>on</strong>e east in Tverrdalen to L<strong>on</strong>gyear valley<br />
and <strong>on</strong>e over <str<strong>on</strong>g>the</str<strong>on</strong>g> Platåbjerget to Bjørndalen<br />
west of Platåbjerget. Lønne and Lyså<br />
(2005) has identified two more, <strong>on</strong>e way<br />
north over Platåbjerget down to<br />
Adventfjorden and <strong>on</strong>e over <str<strong>on</strong>g>the</str<strong>on</strong>g> eastern<br />
lateral moraine toward L<strong>on</strong>gyear valley.<br />
They suggest that <str<strong>on</strong>g>the</str<strong>on</strong>g> way north <strong>on</strong>ly has<br />
been active when <str<strong>on</strong>g>the</str<strong>on</strong>g> way east in<br />
Tverrdalen is blocked and <str<strong>on</strong>g>the</str<strong>on</strong>g> o<str<strong>on</strong>g>the</str<strong>on</strong>g>r has<br />
been active when <str<strong>on</strong>g>the</str<strong>on</strong>g> glacier was thicker.<br />
Today <str<strong>on</strong>g>the</str<strong>on</strong>g>re is a well developed channel<br />
system outside <str<strong>on</strong>g>the</str<strong>on</strong>g> eastern lateral moraine.<br />
Lønne and Lyså (2005) suggest that<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g>re has been an englacial water way<br />
through <str<strong>on</strong>g>the</str<strong>on</strong>g> moraine. They documented<br />
this with mapping of a dead alluvial fan,<br />
this is seen <strong>on</strong> figure 3 as stream line in<br />
different directi<strong>on</strong> middle north of <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
fr<strong>on</strong>tal moraine. With <str<strong>on</strong>g>the</str<strong>on</strong>g> leak of channel<br />
<strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> surface <str<strong>on</strong>g>the</str<strong>on</strong>g>y c<strong>on</strong>clude it to be<br />
englacial water way. Lukas et al. (2006)<br />
means this is just an erosi<strong>on</strong>al feature and<br />
not a build up fan.<br />
Larsbreen is lying in a c<strong>on</strong>fined steepsided<br />
valley and by comparing <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
horiz<strong>on</strong>tal shape of it’s moraine with <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
shape of <str<strong>on</strong>g>the</str<strong>on</strong>g> valley it looks like <str<strong>on</strong>g>the</str<strong>on</strong>g> valley<br />
shape dictating <str<strong>on</strong>g>the</str<strong>on</strong>g> shape of <str<strong>on</strong>g>the</str<strong>on</strong>g> moraine.<br />
The glacier has during <str<strong>on</strong>g>the</str<strong>on</strong>g> LIA pushed <str<strong>on</strong>g>the</str<strong>on</strong>g><br />
rock-glacier at <str<strong>on</strong>g>the</str<strong>on</strong>g> fr<strong>on</strong>t (Humlum, 2005).<br />
This means that <str<strong>on</strong>g>the</str<strong>on</strong>g> rock-glacier has