 |
| Titel |
Sizes and shapes of subglacial bedforms reveal an exponential size-frequency distribution |
| VerfasserIn |
John K. Hillier, Mike J. Smith, Chris D. Clark, Chris R. Stokes, Matteo Spagnolo |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077064
|
|
|
|
|
|
| Zusammenfassung |
| Subglacial bedforms preserved in deglaciated landscapes record characteristics of past
ice-sediment flow regimes, providing insight into subglacial processes and ice sheet
dynamics. Individual forms vary considerably, but they can often be grouped into coherent
fields, typically called flow-sets, that reflect discrete episodes of ice flow. Within these,
bedform size-frequency distributions (predominantly height, width and length) are currently
described by several statistics (e.g., mean, median, standard deviation) that, arguably, do not
best capture the defining characteristics of these populations. This paper seeks to create
a better description based upon semi-log plots, which reveal that the frequency
distributions of bedform dimensions (drumlin, MSGL, ribbed moraine) plot as straight
lines above the mode (Ï). This indicates, by definition, an exponential distribution,
for which a simple and easily calculated, yet statistically rigorous, description is
designed. Three descriptive parameters are proposed: gradient (λ; the exponent,
characterising bedforms likely least affected by non-glacial factors), area-normalised
y-intercept (β0; quantifying spatial density), and the mode (Ï). Below Ï, small
features are less prevalent due to i) measurement: data, sampling, mapping fidelity ii)
possibly post-glacial degradation or iii) genesis: not being created sub-glacially. This
new description has the benefit of being insensitive to the impact of potentially
unmapped or degraded smaller features and better captures properties relating to
ice flow. Importantly, using λ, flow sets can now be more usefully compared with
each other across all deglaciated regions and with the output of numerical ice sheet
models. Identifying the characteristic exponential and that it is typical of ‘emergent’
subglacial bedforms is a new and potentially powerful constraint on their genesis,
perhaps indicating that ice-sediment interaction is fundamentally stochastic in nature. |
|
|
|
|
|
|