Largest active volcano,
largest impact crater, largest lava lake.
Huh, that's funny, they don't have Longest Lava Flow in here – I wonder why that is?
Hi I’m Ali Sealander with UTD GeoNews and today we’re asking the question where on Earth you can find the
longest lava flow? Determining this though can actually be really difficult and we quickly
found ourselves way out of our league. So we turned to world renowned volcanologist
Steve Self, to see what he had to say.
This is a complicated question, but to start with we should first begin to think of -
Thanks for the input Steve!
So if we want to know about Earth's longest lava flows we need to know a little bit about lava first.
The melting of Earth’s mantle produces magma. Once this magma reaches the surface it becomes lava. Not all lavas
are the same, some are able to flow further than others depending on how much silica is in the mix.
This gives us two main types of lava, low-silica basalt and high-silica felsic
lavas. The felsic lavas don’t typically flow as far as the basalts before they solidify,
this is because they have a high viscosity. Viscosity measures how sticky something is,
or ts resistance to flow. Water has a low viscosity
and flows easily whereas molasses has a higher viscosity and flows slowly.
Lava viscosity is determined by silica content and temperature. If a lava has lots of silica,
like the felsic lava, its viscosity will be high and it won’t flow very far before cooling
and solidifying into granitic rock. Basalts contain much less silica and are also hotter.
The higher the temperature the easier the magma flows and the longer it takes to cool.
Imagine how much faster hot molasses flows compared to if it was cold.
So, we can see that the longest lava flows on Earth will likely be basaltic,
now we just need to know which basalt flows. Islands like Hawaii and Iceland erupt a lot
of basalt lava and the slopes of these volcanoes are perfect for making the world’s longest lavas.
But these hotspot volcanoes are surrounded by oceans,
which rapidly quenches the hot lava cutting off a potentially long lava flow.
To find the longest lava flows we need to look for basaltic eruptions on continents,
ideally far away from coastlines. Geoscientists call the greatest
accumulations of basalt lava flows “continental flood basalt provinces”. These areas were buried
by many eruptions of low-viscosity basalt that erupted over periods as short as a million years.
Two of the most famous examples are the Columbia River flood basalts in the Pacific NW of the U.S.
and the Deccan flood basalts of India. The Columbia River Flood Basalts span
large parts of Oregon, Washington, and Idaho. Between about 16 and 10 million years ago,
magma vents in what is now eastern Washington and western Idaho started spewing low viscosity basalt
lava towards the Pacific coast. Steve Self tells us that the longest Columbia River Basalt flow,
vented over the Idaho border and flowed all the way to the Pacific,
making it about 630 km or over 390 miles long! It was cut short by the ocean. You can see the layers
of these flows on the east side of the Columbia River near the small town of Mosier, Oregon, not
far from Portland. Some of the basalts flowed all the way to the Pacific Ocean where they cooled and
hardened to form bulbous, pillow shaped rocks that you can find in Depoe Bay on the Oregon Coast.
Halfway around the world, we have the Deccan flood basalts in India, massive outpourings of lava that
occurred about 66 million years ago, around the time of the end-Cretaceous extinction.
These lavas flowed nearly 1000 km, about the distance from St. Louis to the Gulf of Mexico,
until, once again, they reached the sea off the east coast of India, and may have
flowed farther underwater. So, are these Deccan basalts the world’s longest lava flows? Maybe.
The ocean isn’t the only thing keeping these long lava flows from being longer.
Earth’s tectonic plates complicate things as well. The plates constantly push,
pull, and slide past each other. Over geologic time these movements can rip apart a continent
and hide the evidence of long lava flows on different plates. This is what happened to the
Central Atlantic Magmatic Province, parts of which can be found in the eastern U.S., West Africa,
and northernmost South America. About 200 million years ago, around the same time as the
End Triassic extinction event, the continents were collected together in the supercontinent Pangea.
Basaltic lava flowed out over a massive area on the supercontinent creating,
possibly, the world’s largest lava flow. After the continents separated,
the pieces of the flood basalts were separated by the widening Atlantic Ocean,
like lava puzzle pieces just waiting for a geologist to put them back together again.
As we can see, finding the world’s longest lava is a tricky endeavor. Earth’s landmasses are just too
small to contain its most enormous lava flows. And when these eruptions occur on much larger
supercontinents, plate tectonics splits them up.
Maybe Earth should stick to simpler records
to break, like longest mullet or largest Furby collection, you know, things people care about!
I’m Ali Sealander with UTD Geonews and I’ll see you next time.