![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193749/5_pyroclast.256_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193747/4_plume_back.512_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193746/4_ash.400_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193748/4_plume_front.640_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193745/volcano.1440_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193750/1_magma.240_0_1.png)
lava tube
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193751/2_pressure_vent.128_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193752/3_explode.128_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193753/6_lava.400_0_1.png)
![](/nationalgeographic/pioneer_november_december_2018/inside_an_eruption/193754/7_lahar.400_0_1.png)
InsideanEruption
vent
1
MagmaandgasrisefrombelowEarth’s surface.
2
Risinggasespushonthesealed vent.
3
Gasesexplode,breakingthe seal.
4
Ashandgasshoot upward.
5
Lavaflowsacrossthe land.
6
Theexplosionends.Thesealcloses again.
Restart
magmaand gas
HowItWorks
TheplanwastohiketothetopofSantaMaría.Here,theteamcouldseethelavadomesfromabove.Beforeaneruption,theventofthedomeis sealed.
Magmaandgasesaretrapped.Pressurebuilds.Thesealbreaks.Magmacomesoutas lava.