▁at ▁IMDb ▁▁ ▁Category : N BC ▁News ▁Category : E ducation ▁in ▁the ▁United ▁States <0x0A> </s> ▁A ▁lun ar ▁d ome ▁is ▁a ▁type ▁of ▁shield ▁vol cano ▁that ▁is ▁found ▁on ▁the ▁surface ▁of ▁the ▁Earth ' s ▁Moon . ▁They ▁are ▁typically ▁formed ▁by ▁highly ▁vis c ous , ▁possibly ▁sil ica - rich ▁la va , ▁er upt ing ▁from ▁local ized ▁v ents ▁followed ▁by ▁relatively ▁slow ▁cool ing . ▁L un ar ▁dom es ▁are ▁wide , ▁rounded , ▁circular ▁features ▁with ▁a ▁gentle ▁slope ▁rising ▁in ▁elev ation ▁a ▁few ▁hundred ▁meters ▁to ▁the ▁mid point . ▁They ▁are ▁typically ▁ 8 – 1 2   km ▁in ▁diameter , ▁but ▁can ▁be ▁up ▁to ▁ 2 0   km ▁across . ▁Some ▁of ▁the ▁dom es ▁contain ▁a ▁small ▁cr ater let ▁at ▁the ▁peak . ▁ ▁Some ▁of ▁the ▁dom es ▁have ▁been ▁shown ▁to ▁consist ▁of ▁the ▁same ▁materials ▁as ▁the ▁lun ar ▁mar ia . ▁Thus ▁they ▁could ▁be ▁created ▁by ▁some ▁mechanism ▁that ▁diff ers ▁from ▁the ▁mare - form ing ▁flows . ▁It ▁is ▁thought ▁that ▁these ▁dom es ▁are ▁formed ▁from ▁a ▁smaller ▁mag ma ▁chamber ▁that ▁is ▁closer ▁to ▁the ▁surface ▁than ▁is ▁the ▁case ▁for ▁a ▁mare . ▁This ▁results ▁in ▁a ▁lower ▁pressure , ▁and ▁so ▁the ▁la va ▁flows ▁more ▁slowly . ▁The ▁mag ma ▁well s ▁up ▁through ▁a ▁crack ▁in ▁the ▁surface , ▁but ▁the ▁flow ▁eventually ▁concentr ates ▁through ▁one ▁primary