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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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