lava and surtseyan eruptions

Disney’s Moana – Lava vs. Water

Disney’s recent release ‘Moana’ is not only a great family film but is also a superb film for its geology. Throughout the film geological formations create stunning backdrops, which are pretty accurate in terms of their geological nature. Not only does the film contain some wonderfully animated geological back-drops but also the tale of a lava monster which cannot enter the sea. In terms of real life volcanology how accurate are the tales and imaginings in this film? In this post I’m going to give some insights into the reality of lava vs water and the geological phenomenons shown in Disney’s latest animation.

An island of ancient lava

The island landscape of the film has as similar appearance to that of the Polynesian, or Hawaiian islands within the Pacific Ocean, with sharp jagged mountain peaks and glistening blue waters. At the beginning of the film the geology of Moana’s home island is alluded to with the presence of black lava on the beach. This lava appears to be thin and has an intricately folded ropy surface – this is thin pahoehoe lava. The thin nature of the lava could suggest that this was the leading edge of a lava flow which then froze when its supply of lava, or the source eruption, ended. It may also be possible that larger, thicker amounts of lava are present beneath the white sandy beaches that surround it on this imaginary shore.

Following many years of tradition on the island, the chief places a flat hexagonal rock onto a pile when they begin their ruling. These hexagonal disks of rock are typically found around areas of columnar jointed lavas which have been weathered on the surface of the earth for many years (even many hundreds or thousands of years). The original columns form as a thick lava cools and contracts (columns can also form in dykes and sills). The presence of these special rocks in the film suggests the presence of ancient igneous activity on the island.

Giants causeway
Columnar jointed lava forming hexagonal columns and plates, Giants Causeway, Northern Ireland. Credit: Mayer 2003

Later in the film thick units of these columnar jointed rocks are accurately depicted as huge towering columns like those seen at Devils Tower National Monument in the USA. There has been a lot of debate regarding how the large columns of the Devils Tower formed, with some suggesting that aliens are responsible for these formations! However, columnar jointing like this can be found all over the world, from Scotland to Hawaii, and it is a natural phenomenon that can be explained by the natural contraction of a lava or magma during cooling. Some mysteries still can’t be fully explained, like how such great thicknesses of molten rock can form perfect columns that are several hundreds of meters in length.

Devils Tower National Monument
Devils Tower National Monument made from columnar jointed igneous rocks, USA. Credit: Faulkingham 2003

Lava vs. water

A major part of the film involves a terrifying lava witch which sits in the sea on a small lava covered reef. When Moana comes face to face with this monster she can be heard saying that the ‘lava can’t enter the water’. But, how does this compare to real life?

Hawaii is a prime example of a currently active volcano where lava is actively found flowing into the sea. Most of the time this produces little danger as the lava happily flows off the land and into the sea where it cools into lava rocks, with a hiss and some steam. In the film when the lava witch touches the water the lava of her skin steams and rapidly cools forming a shell of solid lava. This really does happen in the real world. When lava cools rapidly (known as quenching) the outer part of the lava solidifies, it may produce steam and some smaller fragments of rock at the same time. The lava beneath this outer layer may still be molten and will be somewhat insulated by the surrounding skin of cooled rock. The lava witch can be seen explosively expelling the hardened outer shell of skin, after touching the water, to reveal more molten rock inside.

lava and surtseyan eruptions
Lava entering the sea (left) and a typical hydrovoclanic eruption from Surtsey with white steam clouds and black cock’s tails (right). Credit: US Navy, Street 2007 & NOAA

The lava witch is surrounded by the sea and only lies on a relatively thin reef of lava, it is therefore likely that if this was a real eruption then it would be a hydrovolcanic eruption. This would involve large amounts of water coming into contact with magma erupting from a vent. In the film the lava witch is surrounded by black billowing clouds of ash, in reality (for a hydrovolcanic eruption) this is more likely to contain larger amounts of white steam and less black ash than is portrayed. This is because large amounts of water are likely to be involved in the eruption, more so than the amount of ash produced. An exception to this would be if the erupting vent was completely isolated from coming into contact with sea water in which case only a highly explosive eruption would be likely to produce the large billowing clouds of black ash in this way. During hydrovolcanic eruptions the eruption clouds produced often contain episodic black (ash rich) ‘cock’s tails’ rather than continuous billowing black clouds full of ash.

Would a lava monster in the form of a lava flow exist in this situation in reality? The interaction between the lava and water in a hydrovolcanic eruption is typically highly explosive with no actual lava flows produced, unless, the vent was isolated and interactions with sea water had ceased. Therefore the lava witch probably would not exist in this setting until the vent was been sealed off from the sea and the lava was protected and able to flow from the vent.

Conclusion

To wrap up this post delving into the reality of the animated geology of Disney’s film ‘Moana’ it can be said that the geology is very well portrayed. And you can actually learn a few things about volcanology even from an imaginary lava witch!

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