 |
| Titel |
Climate- vs. Earthquake-induced Rock-Glacier Advances in the Tien Shan: Insights from Lichenometry |
| VerfasserIn |
Swenja Rosenwinkel, Angela Landgraf, Oliver Korup, Annina Sorg |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088392
|
| Publikation (Nr.) |
 EGU/EGU2014-2493.pdf |
|
|
|
|
|
| Zusammenfassung |
| Rock glaciers have been traditionally used as landform proxies of the distribution of sporadic
alpine permafrost. In the northern Tien Shan mountains of Kyrgyzstan, most distinct lobes of
>200 rock glaciers that we mapped from satellite imagery occur at two major elevation
levels. However, a number of particularly low-lying lobes seem difficult to reconcile with
palaeoclimatic fluctuations and commensurate changes of permafrost patterns: The
minimum elevation of the majority of rock-glacier snouts lies between ~2500 up to
~3700 m a.s.l., but some 10% of rock-glaciers extend down to well below 3000 m
a.s.l.
We hypothesize that some of the rock glaciers in this area may have formed following
strong earthquakes that could have triggered massive supraglacial rock-slope failures, which
would have subsequently created sediment-rich rock glaciers from clear-ice glaciers. Our
hypothesis is based on the observation that the tectonically active northern Tien Shan of
Kyrgyzstan and Kazakhstan was affected by a series of major earthquakes in the late 19th and
earliest 20th centuries, e.g. in 1885 (Ms 6.9), 1887 (Ms 7.3), 1889 (Ms 8.3), and 1911 (Ms
8.1). All of these earthquakes had triggered numerous landslides in the northern
Tien Shan. It is also likely that similarly strong earthquakes had happened before,
but their recurrence intervals are long and more palaeoseismological work is in
progress.
We test whether lichenometry of rock-glacier surfaces together with morphometric analysis
are suitable methods to testing our hypothesis. We focus on assessing the possibility
of earthquake-triggered rock-glacier advances, and use lichenometry to resolve
age patterns of different rock-glacier lobes. We use a dataset of several thousand
lichen diameter measurements encompassing seven different species calibrated
by gravestones and dated mass-movement deposits. Data on four single and two
merging rock glaciers in four selected valleys in Kyrgyzstan and Kazakhstan support
the notion that Tien Shan rock glaciers do not record a consistent palaeoclimatic
signal.
We discuss whether distinct peaks of comparable lichen sizes and associated distributions
of surface velocities for a given rock-glacier lobe result from rapid climate-driven advances
or high lateral material input provided by seismically-induced slope instability instead. We
compare our field data to advance-rate estimates from ground surveys and remote sensing (1
to >10 m/a), and dendrogeomorphic constraints obtained from trees growing on the rock
glaciers. We conclude by highlighting a number of constraints that may limit the use of
lichenometry for dating rock-glacier advances, and scope for future research on seismic
triggers. |
|
|
|
|
|
|