Náttúrufræðingurinn - 2017, Side 75

75
Tímarit Hins íslenska náttúrufræðifélags
að árétta það. Allar klappirnar eru
sömu gerðar, úr dílabasalti. Einn
einasti rauðleitur klumpur skar sig
úr.
Ég vona að það sannist sem
Tempest Anderson sagði: „Myndir
geta sýnt það sem ekki verður fært í
orð“ (21. mynd).
Nú er orðið tímabært að heilsa
upp á eigendur Hvítanesstanga,
Krist ján Kristjánsson og Sigríði
Hafliðadóttur í Litlabæ, og þakka
fyrir sig. Litlibær er friðlýstur og
á sína sögu. Þar skulum við litast
um og fá okkur kaffisopa og vöfflur
með rjóma. Verði ykkur að góðu.
Summary
Are there pillow lava at Hvítanes
in Ísafjarðardjúp, North-West
Iceland ?
“Iceland is an elevated plateau in the mid-
dle of the North Atlantic … Iceland is
geologically very young and all of its
rocks were formed with in the last 25
million years. The stratigraphic succes-
sion of Iceland extends across two geo-
logical periods: The Tertiary and the
Quaternary.”13 Tertiary rocks in Iceland
consist predominantly of basaltic lavas.
On Hvítanes as porphyritic igneous rock.
Pillow lava is a common feature in-
side the Icelandic moberg mountains,
formed by lava eruptions under ice dur-
ing the glacial periods2 and moberg
forms at the present inside Vatnajökull.37.
The main rocks at the shore of
Hestfjörður pointed to something unu-
sual and very special. My way to get
some ideas about those formations was
to compare them with formations off
the sea of Savaii and Hawaii,3,7,8 coastal
formations formed at higher sea level or
uplift19–23 and on the Mid-Ocean ridg-
es.23–27 As Iceland is on the Mid-
Atlantic-ridge it seemed logical to ex-
pect the same powers at work there as at
the formation of Vestfirðir. The oldest
rock on land being millions years old15
the age decreasing to the east. The
Photographic Atlas of Ballard and
Moore was very helpful.23 To be able to
follow MARBI and NOAA on their re-
search down to the abyss was astonish-
ing. I frequently got stuck there. The
ideas of Vuagnat16 about the shape of
pillows and comparing one type of pil-
lows to “buns” was amusing as lot of
the rocks on Hvítanes seems to fit into
his first category being planio-convex.
What looks like spreading or tensions
crack are quite prominent in different
kinds of rocks on the Hvítanes-peninsula
and seems to conform to the ideas of
Goto and McPhie being diagnostic for
pillow lava.20
I hope what Tempest Anderson said
will be true: “What you cannot describe
in words you can tell with pictures”. At
present I do not know of any papers
about pillow formation in the Miocene
formation on Icelandic seashore. Young
pillow lava that is thought to have
formed on the seafloor is seen in
Dyrhólaey in formation from interglaci-
al periods.31
21. mynd. Klöpp á Landhólma Skötu fjarðar-
megin, gegnt Djúphólma (með þenslurauf-
um?). Tjaldurinn er 40–46 cm á lengd. – A
rock with conspicuous cracks (spreading
cracks?) at Landhólmi. Oyster-catcher for
scale, its length 40–46 cm. Djúphólmi in
background with similar rocks. Ljósm./Pho-
to: Bergþóra Sigurðardóttir.
Heimildir
1. Jón Benjamínsson 1979. Jarðhiti í Ísafjarðarsýslum og Árneshreppi fyrir
norðan Dranga. OS79028/JHD. Orkustofnun, Jarðhitadeild, Reykjavík.
86 bls.
2. Guðmundur Kjartansson 1955. Bólstraberg. Náttúrufræðingurinn 25 (4).
227–240.
3. Anderson, T. 1910. The volcano of Matavanu in Savaii. The Quarterly
Journal of the Geological Society of London 66. 621–639, myndasíður
XLV–LII. https://archive.org/stream/quarterlyjourna661910geol#pa
ge/632/mode/2up/search/Tempest+Anderson+Matavanu (skoðað
24.4. 2017).
4. Anderson, T. 1903. Volcanic studies in many lands. John Murray, London.
444. Eftirprentanir ljósmynda höfundar (m.a. frá Íslandi) með ýtarlegum
skýringum. https://archive.org/details/volcanicstudiesi00ande (skoð-
að 24.4. 2017).
5. Guðmundur Kjartansson 1956. Úr sögu bergs og lands. Náttúru-
fræðingurinn 26 (3). 113–130.
6. Sveinn Pálsson 1945. Ferðabók Sveins Pálssonar. Dagbækur og ritgerðir
1791–1797. Þýð. Jón Eyþórsson, Pálmi Hannesson, Steindór Steindórsson.
Snælandsútgáfan, Reykjavík. 392 bls.
7. Moore, J.G., Phillips, R.L., Grigg, R.W., Peterson, D.W. & Swanson, D.A.
1973. Flow of lava into the sea, 1969–1971, Kilauea volcano, Hawaii. The
Geological Society of America Bulletin 84. 537–546. http://gsabulletin.
gsapubs.org/content/84/2/537 (skoðað 24.4. 2017.)
8. Moore, J.G. 1975. Mechanism of formation of pillow lava. American
Scientist 63. 269–277.
9. Holmes, A. 1972. Principles of physical geology. Frumútgáfa 1965.
Thomas Nelson & Sons, London. 1288 bls. (tilv. bls. 36.)
10. Cutler, A. 2003. The seashell on the mountaintop. How Nicolas Steno
solved an ancient mystery and created a science of the earth. Plume
Penguin Book. 228 bls.
11. Leonardo da Vinci (1452–1519). Yfirlit um vísindastörf Leonardós á vef-
setri Berkeley-háskóla. www.ucmp.berkeley.edu/history/vinci.html
(skoðað 24.4. 2017).
12. Lyell, C. 1998/1880–83. Principles of Geology. Penguin Classics. 528 bls.