Geologic Pictures from Iceland

granodiorite: Iceland has silicic magmatism, too! Presumably, silicic magmas form by (a) partial re-melting of basalt crust at its base (due to deep burial), and/or (b) fractional crystallization of large volumes of gabbro in a magma chamber, leaving a residuum (e.g., Hekla?).

explosion (or collapse) crater lake Grænavatn near Krýsuvík

explosion (or collapse) crater east of Álftavatn

tephra field of the 1104 AD eruption of Hekla This eruption was comparable in volume to the 1980 main eruption of Mount St. Helens in Washington state. It destroyed more than a dozen farms in Þjórsárdalur, and the area has still not been reoccupied.

Isostasy in action

isostatic rebound of a small iceberg (following faster melting of the upper parts, which are exposed to warmer water and/or to weather)

Hvannadalshnúkur: The highest mountain in Iceland is found near the coast, where precipitation, and thus glacial erosion, have been greatest.

All stratified lavas in east Iceland dip to the west: (This is due to loading on top by younger flows to the west.)

layered lava flows north of Jökulsárlón

lavas at Áltafjörður, looking N

a fracture zone scarp(?) in eastern Iceland. The unnamed sinistral transform fault that once connected (and may still connect?) the N end of theWest rift to the S end of the North rift is obscured by surface deposits, but there should still be an imprinted age contrast across a NW-SE line within the Eurasia plate. The NE side should be younger by about 10 Ma, and therefore higher. Even though this fracture zone(?) has not been mapped, and its inactive fault may be buried, one can infer it from the topographic "wall" of mountains just NE of the port town of Höfn (orange dot in this model). Another NW-SE-trending mountain "wall" which might be a fracture zone scarp is found 85 km to the southwest, from Skaftafellsfjöll to Hvannadalshnúkur. Notice the Z-Z shape of the margin of the highlands in this view looking SW across a topographic model.

Erosion of stratified volcanics: waterfalls, columns, & caves

Gullfoss

Seljalandsfoss, #1

Seljalandsfoss, #2

an amazing density of waterfalls (foss)

Dyrhólaey (southern tip of Iceland):

stratigraphy: thick basalt flows (with columnar jointing) over sandur deposits

waves undercut lava flows

small natural arch

Dyrhólaey = "door-hole" arches

basalt column: basalt flows break easily along columnar joint fractures

islets offshore

Longshore transport

black sand beach east of Dyrhólaey

the Fjorur barrier beach

Hydrothermal activity

steam rising from Reykjanes ("Smoking Peninsula")

Krysuvik

solfataras near Krýsuvík, #1

solfataras near Krýsuvík, #2

boiling mud spring near Krýsuvík

geothermal well at farm near Hveragerði

geothermal well at farm(?) in Haukadalur

Geysir geothermal field

general view

a boiling spring

Strokkur

detail of travertine terraces at Strokkur

rocks discolored by hydrothermal alteration

Unusual building materials

turf walls (from inside) at Þjoðveldisbær

a house in Hella

bricks made of pumice

Geodesy

GPS benchmark near Krýsuvík

Disclaimer: The geologic captions for the pictures on this page include a lot of educated guesses. Anyone who thinks, or knows, that I misinterpreted what I saw is encouraged to e-mail me with a correction. P. Bird, 2003.09.15.