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The drumlin problem : streamlined subglacial bedforms in southern Sweden

Dowling, Tom LU (2016) In LUNDQUA Thesis 80.
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling behandlar strömlinjeformade subglaciala bäddformer (ofta kallade drumliner) i södra Sverige. Det övergripande syftet med denna studie är att bidra till en lösning av det så kallade ”drumlinproblemet”. Termen drumlin har kommit att tillämpas på en grupp av landformer vars interna sediment, strukturella uppbyggnad och yttre form kan variera kraftigt. Dessa variationer i egenskaper är delvis förklaringen till de olika konkurrerande teorier som lagt fram om drumlinbildning; ofta har varje typ av beskriven intern sammansättning och/eller yttre morfologi genererat nya/andra tankar om hur drumlinbildningen i det speciella fallet gått till. På grund av mångfalden i föreslagna processer... (More)
Popular Abstract in Swedish

Denna avhandling behandlar strömlinjeformade subglaciala bäddformer (ofta kallade drumliner) i södra Sverige. Det övergripande syftet med denna studie är att bidra till en lösning av det så kallade ”drumlinproblemet”. Termen drumlin har kommit att tillämpas på en grupp av landformer vars interna sediment, strukturella uppbyggnad och yttre form kan variera kraftigt. Dessa variationer i egenskaper är delvis förklaringen till de olika konkurrerande teorier som lagt fram om drumlinbildning; ofta har varje typ av beskriven intern sammansättning och/eller yttre morfologi genererat nya/andra tankar om hur drumlinbildningen i det speciella fallet gått till. På grund av mångfalden i föreslagna processer föredrar jag att benämna landformsgruppen som drumlinoider (’drumlin-liknande’).

I denna studie har ett viktigt hjälpmedel varit den nya svenska nationella höjdmodellen baserad på LiDAR-data från vilken vi kan generera digitala högupplösta digitala höjdmodeller. Detta har kombinerats med detaljerad sedimentologiska undersökningar för att karakterisera strömlinjeformad terräng i södra Sverige och undersöka bildningsprocesser i samband med drumlinoidernas uppbyggnad.

Resultaten av mina undersökningar visar att drumlinoider i södra Sverige är dominant uppbyggda kring en fast bergkärna. Drumlinoider som uppvisar sedimentkärnor tenderar att vara betydligt längre än bergkärnedrumlinoider. I allmänhet ligger drumlinoidformer i södra Sverige i den nedre delen av det storleksspektra som drumlinoider uppvisar inom tidigare nedisade områden i ett globalt kontext. Vidare visar vi att drumlinoider kan bildas under ett kort tidsintevall både i mycket israndnära lägen och längre in under inlandsisen. Den viktigaste kontextuella parametern för drumlinoidbildning verkar vidare vara egenskaperna på och mäktigheten av det underlag i vilka drumlinoidera utformas. Typen av berggrund och det hydrologiska systemet under inlandsisen, som det reflekteras förekomsten av rullstensåsar verkar också spela en viss roll, men den exakta betydelsen av dessa faktorer är inte säker och sambanden är svåra att analysera.

Utöver dessa resultat föreslås en generaliserad konceptuell modell för bildning av drumlinoider kring vilken en diskussion förs om på vilka möjliga sätt olika fysikaliska processer kan påverkar denna bildning. Det föreslås att ett kaotiskt beteende och skalförhållanden ar viktiga parametrar, och även om det kan tyckas i viss mån semantiskt, att det är avsiktligt och viktigt att använda termen drumlinoid för dessa komplexa former. Främsta skälet för det senare är begreppet ’equifinality`, d.v.s. tanken att flera olikartade processer kan leda fram till morfologiskt liknande slutresultat, till exempel att det vi kallar drumlinoider/drumliner har en processmässigt olikartad bakgrund (som bergdrumliner, bergkärnedrumliner eller erosivt bildade drumliner). Dock, även om denna typ av uppdelning är giltig med olika fysikaliska processer involverade i deras bildning så följer de slutliga landformerna ett glacialt form-kontinuum som på överordnad nivå måste betraktas som delar av samma familj. (Less)
Abstract
This thesis investigates stream-lined subglacial bedforms (often referred to as drumlins) in southern Sweden. The broad aim of this is to contribute to the solution of the ‘drumlin problem’. The term drumlin has come to be applied to a wide range of features whose internal architecture (core) and overall morphology are seen to vary greatly. This range in characteristics is in part responsible for the various competing theories of drumlin formation, each different type of core and morphology generating a new idea for how it came about.

Here the new Swedish national height model, a high resolution LiDAR derived digital elevation model, in combination with detailed sedimentological work is used to characterise streamlined terrain in... (More)
This thesis investigates stream-lined subglacial bedforms (often referred to as drumlins) in southern Sweden. The broad aim of this is to contribute to the solution of the ‘drumlin problem’. The term drumlin has come to be applied to a wide range of features whose internal architecture (core) and overall morphology are seen to vary greatly. This range in characteristics is in part responsible for the various competing theories of drumlin formation, each different type of core and morphology generating a new idea for how it came about.

Here the new Swedish national height model, a high resolution LiDAR derived digital elevation model, in combination with detailed sedimentological work is used to characterise streamlined terrain in southern Sweden and investigate the formation processes associated with it.

The findings of this are that drumlinoids in southern Sweden are predominantly rock cored. Soft cored features tend to be significantly longer than rock cored features. In general, drumlinoids in southern Sweden are located at the lower end of the size spectrum in terms of global streamlined sub-glacial features. Additionally it has been found that drumlinoids can form rapidly at glacial margins as well as within the main body of ice sheets. And finally, the most important contextual geological factor in drumlinoid parameter (morphology) formation appears to be drift depth/properties. The bedrock type beneath a feature and the hydrological system as recorded in eskers do play a role, but the exact nature of this is not certain and the correlations are difficult to analyse.

In addition to these findings a generalised conceptual model of drumlinoid formation is proposed and a discussion of the possible ways in which physical processes influence said formation is offered. It is suggested that chaotic behaviour and the role of scale might be useful to consider and that whilst it is something of semantic point, the use of the term drumlinoid is deliberate and important. This is because due to equifinality there are many landforms that researchers can split into different categories, e.g. rock drumlins, clone drumlins, emergent drumlins, downwards emergent drumlins or obstacle drumlins. These are all valid divisions as there are different physical processes involved in their formation. However these processes and the final landforms that result from them are all part of the sub-glacial continuum and so at one level must be considered part of the same family. (Less)
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author
supervisor
opponent
  • Dr Evans, David J.A., Durham Univeristy
organization
publishing date
type
Thesis
publication status
published
subject
keywords
glacial flow, drumlin, self organising maps, LiDAR
in
LUNDQUA Thesis
volume
80
pages
175 pages
publisher
Department of Geology, Lund University
defense location
Department of Geology
defense date
2016-02-19 13:15
ISSN
0281-3033
ISBN
9789187847127
9789187847134
language
English
LU publication?
yes
id
402a85a7-7827-43ed-85f6-36a88b2022de (old id 8569667)
date added to LUP
2016-01-29 09:24:07
date last changed
2016-09-19 08:44:47
@phdthesis{402a85a7-7827-43ed-85f6-36a88b2022de,
  abstract     = {This thesis investigates stream-lined subglacial bedforms (often referred to as drumlins) in southern Sweden. The broad aim of this is to contribute to the solution of the ‘drumlin problem’. The term drumlin has come to be applied to a wide range of features whose internal architecture (core) and overall morphology are seen to vary greatly. This range in characteristics is in part responsible for the various competing theories of drumlin formation, each different type of core and morphology generating a new idea for how it came about. <br/><br>
Here the new Swedish national height model, a high resolution LiDAR derived digital elevation model, in combination with detailed sedimentological work is used to characterise streamlined terrain in southern Sweden and investigate the formation processes associated with it. <br/><br>
The findings of this are that drumlinoids in southern Sweden are predominantly rock cored. Soft cored features tend to be significantly longer than rock cored features. In general, drumlinoids in southern Sweden are located at the lower end of the size spectrum in terms of global streamlined sub-glacial features. Additionally it has been found that drumlinoids can form rapidly at glacial margins as well as within the main body of ice sheets. And finally, the most important contextual geological factor in drumlinoid parameter (morphology) formation appears to be drift depth/properties. The bedrock type beneath a feature and the hydrological system as recorded in eskers do play a role, but the exact nature of this is not certain and the correlations are difficult to analyse.<br/><br>
In addition to these findings a generalised conceptual model of drumlinoid formation is proposed and a discussion of the possible ways in which physical processes influence said formation is offered. It is suggested that chaotic behaviour and the role of scale might be useful to consider and that whilst it is something of semantic point, the use of the term drumlinoid is deliberate and important. This is because due to equifinality there are many landforms that researchers can split into different categories, e.g. rock drumlins, clone drumlins, emergent drumlins, downwards emergent drumlins or obstacle drumlins. These are all valid divisions as there are different physical processes involved in their formation. However these processes and the final landforms that result from them are all part of the sub-glacial continuum and so at one level must be considered part of the same family.},
  author       = {Dowling, Tom},
  isbn         = {9789187847127},
  issn         = {0281-3033},
  keyword      = {glacial flow,drumlin,self organising maps,LiDAR},
  language     = {eng},
  pages        = {175},
  publisher    = {Department of Geology, Lund University},
  school       = {Lund University},
  series       = {LUNDQUA Thesis},
  title        = {The drumlin problem : streamlined subglacial bedforms in southern Sweden},
  volume       = {80},
  year         = {2016},
}