Busy times at the end of the semester right now ...
Concepcion seem from the ISS in 2007. Image courtesy of the NASA Earth Observatory.
One brief bit of news:
Concepcion in Nicaragua erupted, covering three nearby villages with ash. The brief report only mentions 150 meter / 400 foot explosion columns from the eruption, which makes me thing this is merely for the ballastic clasts. No other details - on the eruption or any evacuations - are available.
Concepcion is in the middle of Lake Nicaragua on the island of Ometepe (and the original Mystery Volcano Photo). The volcano last erupted in 2007 and over the last 5 years has been fairly active, producing a number of VEI 2 explosive events (in 2005 and 2006).
At the Smithsonian Institute site they say, "Frequent explosive eruptions during the past half century have increased the height of the summit significantly above that shown on current topographic maps and have kept the upper part of the volcano unvegetated."
I'd be interested to have an idea how many eruptions it takes to grow a volcano. I know some volcanoes grow from growth inside the earth - particularly I am thinking about some Island volcanoes that grow from beneath. Do large volcanoes then grow mostly from material being spouted from the top vent? Are there any formulas for height of volcanoes to historical events?
What do you mean by to grow from below? Do you mean inflation of an existing volcanic system or a diapir pushing up the overlying rock? Generally though, your typical stratovolcano will grow from erupted material. Sometimes they can grow very quickly. Look at Bagana:
I am not sure. There was one volcano whose name I forgot and I just spent about ten minutes trying to find it through Google but couldn't. Anyway this volcano although not very active has risen a lot since Captain Cook landed on it. The spot he landed is now many meters higher due to the growth of the otherwise quiet volcano.
Also Anak Krakatau I think is growing (in part) from being pushed up from below. So I guess I am thinking of inflation of an existing volcano. I am not yet sure what "diapir" is. The link you provided was helpful to show the growth of a little volcano. I'll give some more thought to large volcanoes and how long it takes them to grow. I am pondering if I should think of a linear growth by height or by volume in considering the growth over time of a large volcano. If a volcano is growing by mass ejections, then its height will grow faster at the onset than later.
I appreciate your helpfulness Bruce.
This brings us back to the old debate about the "craters of elevation" - the thought that volcanic mountains are the result of uplift rather than accumulation of eruptive products. That debate was resolved in favor of accumulation rather than uplift, and we know today that volcanic edifices consist of the accumulated products of their own eruptions. Anak Krakatau makes no exception - it's fully grown by accumulation. We've seen, over the years, the growth of a number of cones on Etna here in my backyard, where the process has been wonderfully evident - each eruptive event throws out a certain quantity of material that is deposited on top of the volcanic cone and thus adds to its height.
But there is another way volcanoes grow - by building lava domes. Those domes may grow largely or even entirely by internal accumulation of new lava, which we call "endogenous dome growth", but often lava is also squeezed out at a dome's top, which seems to be happening right now on Montserrat in the Caribbean.
Finally there are volcanoes where magma comes close to the surface but never breaks through to it - is makes a volcano bulge and swell, and thus causes significant ground deformation. The most famous volcano of this type is Usu volcano on the Japanese island of Hokkaido, which last erupted nearly 10 years ago, in the spring of 2000.
I wouldn't call Bagana a small volcano. It's 1750 meters tall (5700 feet). The GVP says that "Bagana is a massive symmetrical, roughly 1750-m-high lava cone largely constructed by an accumulation of viscous andesitic lava flows. The entire lava cone could have been constructed in about 300 years at its present rate of lava production."
That's pretty impressive growth by any account.
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