Volcano question for Rockgremlin and fellow GeoNerds

[DaveOU812]

We took this trip to a volcano out by our house. My wife had a couple of questions that I couldn't answer. For example, how come the middle of the volcano is full of dirt? Shouldn't it be the volcanic rock or pumis? The other one was how come the volcanic rock was diffrent colors. There was big piles of red and brown along with the black. I got some pictures I'll post along with this.

[BrainDamage]

I am a newb when It come to geology, I am just starting on my mining engineering degree.
1. the reason why middle of the volcano is full of dirt is the millions of years of erosion since the lase eruption.
2. The reason for different color of the rocks is the minerals the rock is made of.
I could be wrong on the answers, feel free to correct me if I am wrong.

[price1869]

well, a few million years would be a bit long. Probably more in the tens of thousands or fewer judging from the rock. Different minerals is right for the colors of the rock.

Where do you live? What volcano is it? I'll give you some more info if you can give me the gps coordinates.

Price

[rockgremlin]

Hey Braindamage - You're enrolled in Mining Engineering at the U right? I graduated from the U of Utah in Mining Engineering earlier this year. Great program...watch out for Pariseau and Rock Mechanics!

As Braindamage said, the different minerals in the rock are what give it the colors. Iron oxides are most likely what is giving the rock it's red and brown colors. Iron oxide is the most common coloring mineral in the Earth's crust. In fact, Iron oxide is what lends the sandstones their red colors in southern Utah.

Also as Braindamage and Price stated, after tens of thousands of years, the cinder cone will erode, and fill up with wind-blown silt and sand. Have you ever left a bowl outside for a week or so? Notice how it collects dirt and other silty particles after only a week or so? Same concept applies with volcanos.

[Scott P]

As Braindamage said, the different minerals in the rock are what give it the colors. Iron oxides are most likely what is giving the rock it's red and brown colors. Iron oxide is the most common coloring mineral in the Earth's crust. In fact, Iron oxide is what lends the sandstones their red colors in southern Utah.

Yes, true. Red and brown volcanic rocks come from iron. Interestingly, other volcanoes have different colors, but most are brown or black. Some in Costa Rica have a lot of copper in them, and the some of the rocks are green. This also makes the lakes in the craters green. Check out a photo of the water I took on Poaz:



I took the one below on Irazu:

Also as Braindamage and Price stated, after tens of thousands of years, the cinder cone will erode, and fill up with wind-blown silt and sand.

Ture, and sometimes even less on soft cinder cones. Some of them only four thousand years or so old already have significant sand and dirt on and in them.

[rockgremlin]

Spectacular photos Scott!

Hmmm....I wonder just how much copper is in that water? And how much it would cost to harvest it?

Just kiddin'

[Scott P]

And how much it would cost to harvest it?

I don't know, but I you had better act fast. Below is the volcano very near the ones in the other two photos posted above. It was cool to see the thing go off (from a distance of course).