How are the different volcanoes different?

Answer 1

I think you are asking about the difference between

Explosive volcanoes that shoot off their tops, like Mt St Helens, and spread volcanic ash high into the air while dropping lava bombs nearby amongst the lava flowing out from cracks.

and

Shield volcanoes which keep adding laval in a less explosive manner so it just builds up forming a shallow cone with a hole in the center, resembling the shield of a greek warrior.

Here's how they are different:

Shield volcanoes, as in the Hawai'i have basaltic magma which is runnier than the granitc magma that rises to erupt from continental volcanoes.

Magma with lots of iron and manganese cools as it rises. Every so often, the magma gets too cold for a rock type to continues to be melted and that part makes a crystal which is solid. The crystals are left behind when the magma rises, and as it keeps moving up, more and more solids drop out of the melt.

Finally, most of the iron and magnesium dropped out as crystals and now you have the magma dregs: silica, gold, etc. beryl.

Silicate lavas are very sticky and viscous. It takes more pressure to get that sticky silicate goo upward and away from the volcano compared to eruptions of basaltic lava.

Try it yourself using sugar 2D links

1. Put a bunch of rocks on a tray

2. make fudge

3. quickly pour it over the rocks

4. compare your fudge lava to aa features in Hawaii

Silica is tougher, it has 3D links

1. set up a piece of wax paper hanging from the ceiling over a tray of water

2. melt sugar until it is a liquid

3. carefully place spoon in sugar with both hands, take up a small part of melted sugar and throw it at the wax paper

4. compare the shpae of the cooled sugar to pics of lava bombs

thats the difference - silica bonds in 3 dimensions