Jökull - 01.01.2021, Page 57

Bedrock and tephra layer topography within the Katla caldera
Figure 8. a,b) Interpolated maps showing ice thickness above the 1918 (a) and a deeper tephra layer (b) in
September 2016. Grey lines and clusters indicate locations of traced tephra layer reflection. The dash-lined
box in a indicates the area zoomed in on Figure 11. c) An example of 2D migrated RES-profile, location from
A to B (a) showing both tephra layers and bedrock. The image is a mosaic of a 2D migrated profile, applying
masking of bedrock reflections prior to migration (see Data and Methods for further details) for the englacial
reflections, and the normal 2D migrated profile without masking of bedrock reflections; the grey scale image for
the englacial reflections corresponds to weaker backscatter than for the bedrock reflections. d) Cross-section at
the ice divides between Entujökull and Kötlujökull, from location C to location D on (b), and inserted images)
showing the glacier surface in September 2016, the interpolated bedrock and the interpolated tephra layers in
September 2016. For comparison, the elevation of various isochrones, obtained from a static velocity field
(Jarosch et al., 2020; see main text for further details), are shown for September 2016 at three locations where
RES-profiles cross the ice divides. The inserted images indicate the locations of traced bedrock and tephra layer
reflections.
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