![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192302/5_pyroclast.256_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192300/4_plume_back.512_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192299/4_ash.400_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192301/4_plume_front.640_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192298/volcano.1440_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192303/1_magma.240_0_1.png)
lava tube
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192304/2_pressure_vent.128_0_1.png)
vent
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192305/3_explode.128_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192306/6_lava.400_0_1.png)
![](/nationalgeographic/trailblazer_november_december_2018/inside_an_eruption/192307/7_lahar.400_0_1.png)
InsideanEruption
1
MagmarisesfrombelowEarth’s surface.
2
Risinggasesputpressureonthesealed vent.
3
Gasesexplode,breakingthe seal.
4
Ahotcolumnofvolcanicashandgasshootsintothe air.
5
Duringlargeeruptions,pyroclasticflowsmadeofgasandvolcanicmattermoveathigh speeds.
6
Lavaflowsslowlyacrossthe land.
7
Lahars,mixturesofwaterandash,moverapidlydownstreamsand rivers.
8
Oncethegaseshaveescaped,theexplosionends.Thesealcloses again.
Restart
magmaand gas
HowItWorks
TheplanwastohiketothetopofSantaMaría.Here,theteamcouldobservethelavadomefrom above.
InsidetheCalientedome,magmaandgaswererising.Beforeaneruption,theventofthedomeissealed.Magmaandgasesaretrapped.Pressurebuilds.Theseal breaks.
Whenthesealbreaks,gasisreleased.Magmaoozesoutaslava.It flowslikethickrivers.Ashisforcedhighintothe sky.
Thensomeofthematerialresettlesoverthevent.Theventsealsagain.Thepressurebeginstobuildagainuntilthenext eruption.