Jökull - 01.12.1982, Page 22

steady-state conditions under which the inland
jtlateau was built. Since then, a more or less uniform
uplift of both areas has occurred to generate the 650
m surface.
AVERAGE EROSION RATE
The average elevation of the Austfirðir, based on
the height above sea level (on the 1:100,000 maps)
of 2700 points on a rectilinear grid, is 400 m; the
average lowering of the surface was thus 900 m in 12
m.y., giving an overall average lowering rate of
1 mm per 13 years. The total rock eroded away from
the Austfirðir is 4100 km3, equals 1 km3 per 2900
years; this does not include the very considerable
amount eroded offshore east of the Austfirðir.
ACKNOWLEDGEMENTS
The field work was done 20years ago while at Imperial
College, London, and was made þossible by the financial
support of the Icelandic National Research Council, the
Fjórðungsthing Austfirðinga, and the Royal Society; also
by the help, hospitality, andfriendship of many Icelanders.
Hawaii Institute ofGeophysics Contrib., no. 1307.
REFERENCES
McDougall, L, N. D., IVatkins and L. Kristjánsson,
1976: Geochronology and paleomagnctism of a
Miocene-Pliocenelava sequenceat Bessastadaá,
eastern Iceland. Am. J. Sci., 276: 1078— 1095.
Walker, G. P. L., 1960: Zeolite zones and dike dis-
tribution in relation to the structure of the bas-
alts of eastern Iceland.J. Geol. 68: 515-528.
Walker, G. P. L., 1974: The structure of eastern
Iceland. In: Geodynamics of Iceland and the
North Atlantic area. L. Kristjánsson (ed.), Reidel
Publ. Co., Dordrecht, 177 - 188.
Watkins, N.D. and G.P.L. Walker 1977: Magneto-
stratigraphy ofeastern Iceland. Am. J. Sci., 277:
513-584.
Manuscript accepted 24 May 1982.
ÁGRIP
ÞRÓUN LANDSLAGS Á AUSTURLANDI
G.P.L. Walker, University of Hawaii
I greininni er könnuð landmótunarsaga Aust-
fjarða og hluta hálendisins upp af þeim, og áætlaður
er hraði rofs á þessu svæði. Hásléttan sem þetta rof
hefur verið að vinna á, varð upphaílega til fyrir 12
millj. ára (austast) til 2.5 millj. ára (vestast), og út
frá legu ummyndunarbelta í staflanum telur höf-
undur að hún hafi náð upp 1 700-1500 m hæð.
Greina má ummerki um að Austfirðir hafi þrívegis
lyfzt upp nokkuð snögglega; eftir síðustu landltækk-
unina hafa vatnaskil stöðugt verið að flytjast vestar.
Meginuppspretta eldvirkni á Austurlandi hefur
ennfremur færst suður á bóginn sl. 5 millj. ár, og
hefur það haft veruleg áhrifá þróun landmótunar á
Fljótsdal og jökuldal.
20 JÖKULL 32. ÁR