Plot a terrain relief of Erebus volcano with contour lines.

erebus.md

library(data.table)
library(ggplot2)
library(metR)

out.file <- "~/Downloads/erebus_atm_2001_dem_v5.tif"
if (!file.exists(out.file)) {
   # data => https://www.pgc.umn.edu/data/elevation/
   # ~ 90Mb   
   download.file("http://data.pgc.umn.edu/elev/dem/atm/2001/erebus_atm_2001_dem_v5.tif",
                 out.file)
}

erebus <- tiff::readTIFF(out.file)
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 33550 (0x830e) encountered
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 33922 (0x8482) encountered
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 34735 (0x87af) encountered
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 34736 (0x87b0) encountered
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 34737 (0x87b1) encountered
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 42112 (0xa480) encountered
#> Warning in tiff::readTIFF(out.file): TIFFReadDirectory: Unknown field with
#> tag 42113 (0xa481) encountered
erebus[erebus == -9999] <- NA
dimnames(erebus) <- list(x = seq_len(5004), y = seq_len(4504))
erebus <- setDT(data.table::melt(erebus))
erebus <- erebus[!is.na(value)]

binwidth <- 15
ggplot(erebus[y %between% c(1500, 2500) & x %between% c(2000, 3500)], aes(x, y)) +
   geom_relief(aes(z = value), alpha = 1) +
   geom_contour2(aes(z = value, size = ..level.. %% (binwidth*2)), 
                 binwidth = binwidth, 
                 color = "black") +
   scale_x_continuous(expand = c(0, 0)) +
   scale_y_continuous(expand = c(0, 0)) +
   scale_size(range = c(0.1, 0.2), guide = "none") +
   coord_equal() +
   theme_void()