Science, Hollywood, a smiling volcano…. What do those things have in common? The Disney/Pixar short film presented with Inside Out! Science in films is not often successful or “scientific”. Just have a look at 2012, The Core, Japan sinks, Volcano, Dante’s peak, and maybe many others. Therefore it is a nice surprise to see that there can be science below this recent short film called “Lava”.
This film tells the story of a volcanic island “in the middle of the sea”, from its active state to its extinction. It’s based on Big Island (Hawaii) and its evolution. I propose you have a look at the science of “Lava” just by following the lyrics.
A long long time ago
There was a volcano
Living all alone in the middle of the sea
Where is this volcano from and why is “he” alone? It’s a hotspot volcano! Reminder: a hotspot (that relates to intra-plate volcanism) is one of the three different sources of volcanism on Earth. It is an assumed fixed place in the lower mantle which is unusually hot where material upwells as a plume (like in a lava lamp), reaches the lithosphere and provides magma at the surface. The source can be either on the limit between the upper and the lower mantle, or in the D” layer at the mantle/core boundary, depending on the hotspot. As plates are moving and the plume is not, different volcanoes are created for one source, and they are easily recognizable with their alignment (image 6). There is a huge amount of hotspot volcanoes on Earth, which in the oceans can grow high above sea level and form well known (inhabited) islands such as the Hawaiian Emperor chain, La Réunion island and Mauritius, Canaries, Polynesian islands and Comoros, but they can also be on continental plates as in Yellowstone, eastern Australia Cosgrove track and Antarctica… An animated GIF to see some of them is provided below.
Every day for years and years…
The “life time” of this kind of volcano depends on the velocity of the tectonic plate because the volcanoes should be fed by the lava coming from the hot spot to be active. As soon as the hot spot is no longer below the volcanoes, its activity stops. For Hawaii, the Pacific plate is “fast” (geologically speaking) with a displacement of 10 cm/year; on the opposite, the African plate moves only 2cm/year. Thus Big Island (the youngest volcanic island of Hawaii) in the Pacific ocean is 400.000 years old while La Reunion in the Indian ocean island is 2 million years old.
Here is to singing all alone
Poor sad single volcano… Usually hotspot volcanoes are not isolated like this, often there’s an older or younger volcano on the same island or on a neighbour one. In La Réunion and Big Island, there are several volcanoes (see pictures below) on the same island. Just assume that our hero is the first volcano of the island (as Mauna Kea or Piton des Neiges) and that a second one (Mauna Loa or Piton de la Fournaise) will grow so next to “him” that they will be part of the same island. Back to the story, he should be able to see Haleakalā!
and turning his lava into stone
Beyond the stylistic effect, lava (not love), degassed magma which has reached the surface, cools and solidifies forming different volcanic rocks. The nature of the rock depends on the composition of the magma. For hotspot volcanoes the magma can range from basalt to andesite compositions (image 5). But only a small percentage of the magma released by the magma chamber reaches the surface and forms volcanoes and islands. Generally, the magma is going up either through fractures, creating dikes, or along lithologic contacts (surfaces that separate rock bodies of different nature or lithologies), creating sills and dikes. In that case the magma cools slowly at depth, crystallizes, and eventually gives plutonic rocks such as gabbro, syenite and diorite that have the same chemical composition of their volcanic analogs but with larger crystals (picture below).
Until he was on the brink of extinction
In this part of the film the volcano is barely reaching the surface of the ocean, it is “on the brink of extinction”, and a ring is visible all around the central crater. This is the last stage of evolution of a volcanic island. After the construction phase, when the plume located under the island stops feeding the volcano with lava, the erosion by wind and water is no longer compensated by the input of new volcanic rocks, and the topography starts decreasing. With this erosion, the island’s emerged and immerged slopes are lowered creating a shallow platform all around the island where coral barrier reefs can form (coral forms in shallow warm (tropical) water). In the end only these constructions remain along with some beaches of sand; it’s now an atoll (French Frigate Shoals, Maldives). This evolution is easily understandable with a satellite view (image below).
But little did he know
that living in the sea below
was listening to his song.
Everyday she heard his tune
her lava grew and grew
And there is the new volcano!
Examples in the world? In Hawaii a new volcano on the South East coast of Big Island is currently being formed but has not yet reached the sea surface, called the Loi’hi Sea Mount (picture above).
Rising from the sea below
stood a lovely volcano
The new volcano appears by a huge surtseyan eruption. This type of eruption has been reported for the first time for Surtsey island in Iceland.
looking all around but she could not see him.
He tried to sing to let her know
that she was not there alone
but with no lava of his his song was so gone
Occasionally, there can be a final period of activity associated to the old volcano which enables “him” to reach once again the surface of the ocean. It is a common feature for volcanic islands. The magma chamber of the oldest volcano is still linked to the deep supply (the hot spot) even if it is now located under the second volcano. With increasing distance from the magma source the activity will progressively and definitely stop. This is the case in La Réunion; Piton des Neiges (the oldest) and Piton de la Fournaise (the youngest) had a period of synchronal activity some million years ago, but nowadays only the second one is active. But they will all inevitably evolve in atolls and fade out under the ocean surface.
Oh they were so happy
to finally meet above the sea.
All together now their lava grew and grew.
No longer they are they all alone
with Aloha as their new home.
And when you go and visit them this is what they sing
They lived happily ever after…(or not?)