January 23 – Mauna Loa Begins 300-Day Eruption

Posted on January 23, 2017

I think of volcanoes erupting over a matter of minutes or hours – not for the better part of a year!

But that's because I think of volcanic eruptions as violent explosive outbursts of lava and gas and steam. Mauna Loa, in Hawaii, is the largest volcano on the planet partly because its lava tends to be silica poor, and therefore the lava eruptions tend to be very fluid, non-explosive, gentler and slower-moving than many other volcano's eruptions, although often still quite destructive.

So...why does having silica-poor lava relate to being a large volcano? Simply stated, Mauna Loa doesn't blow off its top!

These pictures of another volcano, Mt. St. Helens,
shows that some volcanos DO blow their tops off!
Check out the lovely cone that is Mauna Loa, below:

The slopes of Mauna Loa are generally gentle. The cooling lava makes the volcano larger – and, incidentally, makes the island of Hawaii larger. The volume of the volcano is estimated to be about 18 thousand cubic miles (75 thousand cubic kilometers).

By the way, even though Mauna Loa is the largest volcano on Earth, we are talking about that huge volume, not its height. It isn't the highest volcano on Earth, and even its island neighbor, Mauna Kea, is higher by about 120 feet (37 meters).

Now, about that 300-day eruption!

On this date in 1859, Mauna Loa had a brief summit eruption. Then a stream of lava broke out from the volcano's flank (side), high up but not at the top. This outbreak of lava created a 32-mile-long lava flow, the longest in the state of Hawaii.

On the evening of January 30 the lava began to destroy the village of Wainanali'i on the west coast of the island. I gather that no lives were lost, but some people lost everything they owned as well as their homes. However, since Mauna Loa's lava moves relatively slowly, many people were able to gather their most precious belongings and personal effects before escaping to higher ground.

By January 31 the lava reached the ocean. This was eight days after the eruption started – and, amazingly, the eruption continued another 292 days! As the lava continued to flow, it filled fishponds and of course impacted the economy of several communities.

The science of volcanology was extended during this eruption, since a'a and pahoehoe lava flows could be studied and compared. It turns out that the two kinds of lava are identical chemically; the difference is in their temperature. A'a lava flows become cool enough that they cannot flow, and so a more broken-up, rougher rock forms, compared to the smooth-flowing pahoehoe lava flows.

A'a lava forming, above,
and cool a'a lava, below.

Pahoehoe lava forming, above,
and cool pahoehoe lava, below.

Also on this date:

Anniversary of a Record-Setting Dive 

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