The Thermal Evolution of Western Norway Based on Multi‐Sample Models of an Elevation Transect: Implications for the Formation of High‐Elevation Low‐Relief Surfaces on an Elevated Rifted Continental Margin
Åse HestnesDeta GasserRichard A. KetchamIstván DunklAnna K. KsienzykThomas ScheiberHallgeir SirevaagJoachim Jacobs
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Abstract The post‐Caledonian thermal and geomorphological evolution of onshore Western Norway is poorly understood, including the formation and age of the high‐elevation low‐relief surfaces seen across the Norwegian landscape. We present new apatite fission track (AFT) and (U‐Th‐Sm)/He analyses from an elevation transect (ET) covering ∼1,800 m vertical distance below a high‐elevation low‐relief surface in the inner Nordfjord. The AFT ages increase with elevation from 159 ± 11 Ma to 256 ± 21 Ma and apatite (U‐Th‐Sm)/He ages increase with elevation from 80 ± 4 Ma to 277 ± 15 Ma. In order to test different possible thermal evolutions, we present the first multi‐sample thermal history models from Norway using HeFTy combining both AFT and (U‐Th‐Sm)/He ages along the ET, refining available thermal history models for the area considerably. The best modeling results are found for a thermal evolution with slow cooling throughout the Mesozoic and increased cooling rates from the Late Cretaceous until present, indicating a Cenozoic age for the low‐relief surface at the top of the transect. The models also allow for cooling to surface conditions in the Late Jurassic, but such an evolution must have been followed by rapid burial by 1.5–3 km Cretaceous sediments, and by re‐exhumation in the Cenozoic, indicating that the low‐relief surface cannot represent a simply uplifted Jurassic or Cretaceous peneplain. We compare our results with multi‐sample models from the wider North Atlantic region, supporting previous findings of Cenozoic exhumation and landscape forming processes within that region.Keywords:
Elevation (ballistics)
Continental Margin
This paper aimed to investigate the influence of climatic and topographic factors on the distribution of vegetation in the Virunga Volcanoes Massif using GIS and remote sensing techniques. The climatic variables considered were precipitation, Land Surface Temperature (LST), and evapotranspiration (ET), whereas the topographic factors considered were elevation and aspect. The dataset consisted of MODIS NDVI data, satellite-delivered precipitation, ET, and the LST. A 2014 Landsat 8 OLI image was used to produce a vegetation map of the study area, while DEM was used to derive the elevation attributes and to calculate the aspect angles. Moran’s I and Geographically Weighted Regression (GWR) Model was used to analyze the relationships between the climatic factors and NDVI changes over elevation and aspect. The results indicated that among the nine vegetation types inventoried in the area, the Mean NDVI varied from 0.33 to 0.59 and the optimal vegetation growth was found at an elevation between 2000 and 3900 m, with mean NDVI values larger than 0.50. The peak mean NDVI value of 0.59 was found at the elevation from 2100 to 2800 m. Vegetation growth was found to be more sensitive to elevation, as NDVI values were more varied at a lower elevation (<4000 m) than at a higher elevation (>4000 m). Considering the aspect, the greater vegetation growth was found in SE (132°, 148°), SW (182°, 186°), and NW (309.5°–337.5°), with mean NDVI values larger than 0.56. This indicated that vegetation was susceptible to better growth conditions in the lower elevation ranges and in shady areas. The vegetation NDVI in this study area was mostly uncorrelated with precipitation (R2 = 0.34), but was strongly correlated with LST (R2 = 0.99) and ET (R2 = 98). LST (≥18 °C) and ET (1286 mm/year−1) were found to provide optimal conditions for vegetation growth in the Virunga Volcanoes Massif. Empirically, the results concluded that elevation, aspect, LST, and ET are the main factors controlling the spatial distribution and vegetation growth in this area. This information is significantly helpful for biodiversity conservation and constitutes a valuable input to environmental and ecological research.
Elevation (ballistics)
Massif
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With the combination of gradient analysis and quantitative analysis of landscape pattern,and by changing the transect width and research step,the extent effect of landscape gradient analysis of an urban-rural transect were studied.The results showed that the landscape gradient analysis of the urban-rural transect was scale-dependent,and the effect of transect width was greater than that of research step.Research step mainly affected the fluctuation degree of each landscape index along transect,and it was appropriate for the transect to be divided equally into 20 samples.There existed critical values for transect width.When the transect width was beyond the values,the fluctuation trend of each index along transect would be varied.Furthermore,different landscape metrics responded differently to the same transect.The percent coverage and edge density of each class,as well as the Shannon's diversity index of landscape,showed significant gradient characteristics,while patch density and mean patch fractal dimension were in adverse.
Belt transect
Diversity index
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Elevation (ballistics)
Massif
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Elevation (ballistics)
Basal area
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