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5. The basalts of the Blosseville Coast

The basalts of the Blosseville Coast

Wel­ded tog­e­ther during the Cale­do­ni­an oro­ge­ny, seve­ral con­ti­nents had remain­ed as one huge land mass during seve­ral hundred mil­li­on years. Final­ly, the break-up of this lar­ge con­ti­nent was on its way during the later Meso­zoic. In the north, it hap­pen­ed bet­ween East Green­land and nor­t­hern Euro­pa (Ireland/Scotland/Scandinavia) in the lower Ter­tia­ry, 50-60 mil­li­on years ago. This pro­cess of brea­king up (‘rif­ting’) led to inten­se vol­ca­nism about 55 mil­li­on years ago, simi­lar to Ice­land today. Lar­ge volu­mes of basal­tic lava cover­ed wide are­as. The­re are no vol­ca­nic moun­ta­ins with the clas­si­cal cone-shape visi­ble, as the erup­ti­on cen­tres were total­ly buried under their own pro­ducts.

Layers of basaltic lava in eastern Gåseland

Lay­ers of basal­tic lava in eas­tern Gåse­land. The laye­ring is opti­cal­ly even enhan­ced by the fresh snow and pro­vi­des a strong con­trast to the unlaye­red meta­mor­phic rocks seen in the lower slo­pe.

Erup­ti­ons lar­ge­ly hap­pend during three stages.

During the first stage, the erup­ti­on cent­re was pro­ba­b­ly some­whe­re at Gåse­land. Lar­ge volu­mes of liquid basal­tic lava fil­led the old val­leys to begin with, befo­re they could start to cover the who­le area. Then, a sin­gle lava flow, being 10-50 m thick, could cover as much as 4000 km2!

The cent­re of the second stage was near the outer coast of today. Nevert­hel­ess, the lava flows which were pro­du­ced here went as far as 120 km, rea­ching among­st others Gåse­land. During the third stage, ever­y­thing was cover­ed with basal­tic lava flows once again, befo­re a lar­ge num­ber of intru­si­ons pene­tra­ted both the basalt lay­ers and, to a les­ser degree, rocks in other are­as in the Score­s­by­sund such as in Jame­son Land.

The dif­fe­rence bet­ween the three stages is not imme­dia­te­ly evi­dent to the visi­tor in the field, but it beco­mes clear to sci­en­tists from detail­ed inves­ti­ga­ti­ons in the field and in the labo­ra­to­ry, inclu­ding the che­mis­try of the lava rocks.

The total thic­k­ness of the basalt lay­ers has its maxi­mum near the outer coast and rea­ches more then 2000, in places even more then 3000 met­res. An area of at least 80 000 km2 was cover­ed.

Com­pared to today’s vol­ca­nism on Ice­land, the fre­quen­cy of erup­ti­ons 55 mil­li­on years ago in the area south of the Score­s­by­sund was a bit less, but the volu­mes of erupt­ed lava was much lar­ger.

The lay­ers of basal­tic lava now form striking land­scapes south of the Score­s­by­sund and in sou­thern Mil­ne- and Gåse­land. The sin­gle lay­ers, each repre­sen­ting a lava flow, are well visi­ble and lay more or less hori­zon­tal­ly. The­se rocks are quite hard and thus form a high pla­teau, which is most­ly gla­cia­ted and now dis­sec­ted by indi­vi­du­al gla­ciers. The slo­pes are usual­ly extre­me­ly steep, the land­scape is quite inac­ces­si­ble and lives the visi­tor with an impres­si­on of inhos­pi­ta­bi­li­ty.

Basalt cliffs at the Blosseville Coast (outer coast south of Scoresbysund) near Nansen Fjord

Basalt cliffs at the Blos­se­ville Coast (outer coast south of Score­s­by­sund) near Nan­sen Fjord

Inten­se land uplift which hap­pen­ed tog­e­ther with the vol­ca­nism in the lower Ter­tia­ry is of decisi­ve importance for the appare­an­ce of today’s coast­li­ne in most parts of Green­land (and Nor­way). The Cale­do­ni­an moun­ta­ins had been ero­ded sin­ce long ago, all the­re was left was a land­scape of low-lying hills. It nee­ded uplift of seve­ral 1000 met­res to crea­te the spec­ta­cu­lar moun­tain and fjord sce­n­ery which we can admi­re in East Green­land nowa­days. This hap­pen­ed during the ope­ning of the north Atlan­tic. Remains of the old low­lands now form the rol­ling, most­ly gla­cia­ted high pla­teau in the inner Score­s­by­sund (Mil­ne Land etc.), whe­re it has not yet been com­ple­te­ly des­troy­ed by ero­si­on.

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last modification: 2013-10-12 · copyright: Rolf Stange
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