Geology Tristan, along with its neighbouring islands, lies about 400 km east of the Mid-Atlantic Ridge. The volcanic activity is unrelated to the Mid-Atlantic Ridge; rather, it is due to a hotspot. The steep central cone (The Peak) predominantly is composed of pyroclastic deposits erupted from the central vent. The Base and Main Cliffs are composed mainly of thin basaltic lava flows, commonly separated by thin pyroclastic layers. There are over 30 cinder cones on the flanks of the main volcano, many of which have produced small lava flows. The October 1961 eruption was preceded by earthquake swarms and rock falls from the Main Cliffs, then lava was erupted on the plain immediately east of the settlement. The growing lava mound breached and lava flows were erupted toward the coast. As the eruption waned, an elongate lava dome grew and sealed the vent.
GEOlogy tristaN, along With iTS NeIghbOUring Islands, Lies abOUT 400 Km eAst oF The mid-atlAntic riDgE. The voLCanic actiViTy is unreLAt,eD To thE mid-AtLanTic RiDGe; rathEr, IT is dUe to a hoTspOt the steEP central cone (the peaK) predoMInantly is coMpoSeD Of pyrOcLastic DEpOsits erUptED FROm The cENtraL VEnT. tHE baSE And Main cliffs Are comPOSed mAINly Of thIn baSaltic lAva flOws, cOmmonly sepARaTEd By thIn pyroclastic lAyErs. thERe arE oveR 30 ciNDeR cones on the flAnKS Of the maiN vOlcANO, many of WHIcH have prodUced sMALl lava flows tHe october 1961 EruPtion Was pRecEded By earthQuAke SwaRMS AnD Rock fAlls frOM the maIN cliffs then lAva waS eru.PTeD oN tHe plAIn iMmeDiaTEly eASt OF THe sETtLeMeNT. thE Growing LaVa mouNd brEACheD AnD lava floWs were eRUPteD TowaRd ThE coast. As The. eruPtion wanEd, an EloNgate lavA domE grew anD sealed THe vEnt.