Abstract
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The flanksofmid-oceanvolcanoesareinherentlyunstablefeaturesespeciallyintheconstructionalphase
of developmentwhenthevolcanoisactive.Lateralandverticalstressesareplacedonthevolcanicedifice
as itbuilds,withtheflankscontinuingtobeunstableuptoatleast1Maaftervolcanismhasceased.The
flanksoftheLordHoweIslandvolcanorecordthisperiodofgreatestinstabilityandasubsequentperiodin
which marineandsubaerialerosionhavedominateditsgeomorphicevolution.LordHoweIslandliesin
the TasmanSeaoftheSouthernPacificregionandisthesubaerialremnantofaMiocenemid-ocean
volcano. Theislandhasonlyrecentlyenteredreefbuildingseasandthereforehasbeensubjecttomarine
erosiveprocessesoverthepast5–6Ma.Theislandisuniqueasitsitsonthestabledrownedcontinental
crustoftheLordHoweRiseratherthanoceaniccrustlikemanyothermid-platebasalticislands.
Multibeamsonarbathymetrydatawerecollectedtoadepthof3500mwheretheislandflanksgradeinto
the surroundingplanarseafloor.Severalslumpfeaturesareevident,thelargestbeingover130km2 in
area. Thesefeaturesareinferredtobeold(lateTertiary)basedonanextensivecoverofmarinesediment
as indicatedbylowmultibeambackscatterintensityandsubduedtopography.Mostlikelytheslumps
formedduringtheimmediatepost-eruptivestageofvolcanoevolution,beforethebulkofthesubaerial
portionofthevolcanowasremovedbymarineerosion.Flankprocessesarenowdominatedbythe
depositionofcarbonatesedimentcomposedofmolluscandforaminiferalremains.Basedonradiocarbon
and stableisotopeanalysesofasedimentcore(760mdepth)collectedonatroughinthecentreofthe
volcanicedifice,Quaternarysedimentwaslikelydepositedpredominantlyduringglacialperiods.The
erosionalmorphology,sedimentcoverandtectonicstabilityoftheregionsuggestthattheflanksofthe
volcano areatpresentrelativelystable.