|Alison observing lava coming out of the ground, and lots of gas. In this case SO2, sulfur dioxide. Even if we know more about volcanoes than we used to, direct observations are an important part of the process of understanding them better.|
These models are based on evidence, and we must collect said evidence (observations, test results etc). Natural phenomena occur at incredibly small and incredibly large scales, and everything in between. This makes it particularly challenging to observe everything that is happening, so we break it down into smaller pieces and then try to come up with a model that agrees with all the parts. Our ability to make observations has frequently been technology limited. Before we had the ability to blast rocks with X-rays (and now lasers, electron beams and other cool stuff) we could describe the minerals in a rock, but we couldn't say much about exactly how much of certain elements were in the rock (there was some wet chemistry that helped some, but man was it time consuming and hard to get a representative result). We can make all sorts of educated guesses about what happens under a volcano by looking at old eroded volcano plumbing systems, but if we want to say something about a specific active volcano we need to be able to say something about what is happening underground. We now have lots of new awesome techniques looking at small variations in gravity and how seismic ways speed up and slow down (geophysics) that help us estimate where hot rock is under volcanoes. This is a huge advance, but there are still lots of complexities about the subsurface that leave us with questions, some we didn't know to ask before.
|Technology lets us look at Earth, other planets and volcanoes in lots of new ways. At the center of the image you can spot Momotombo in Nicaragua with active lava flows in December 2015. More information on this infrared image from the ALI instrument via NASA photojournal.|
So what does this all have to do with volcanoes in space? Let’s look at some really general models of volcanoes. What is a volcano? That is easy right? It is a spot on the Earth where lava and gas comes out. Do all volcanoes look the same? Nope! They come in lots of shapes and sizes. Ok, but we still call them all volcanoes because they do the same basic thing. Geologists started looking at different volcanoes and seeing which were most alike, and which weren’t and then came up with the major types of volcanoes. So now when you take an Earth Science class you usually learn about the major shapes of volcanoes: scoria cones, stratovolcanoes, shield volcanoes, calderas, and don’t forget the maars! What makes them difference is what type of lava comes out, how much, how fast, and what it comes in contact with on the way. So that really simple definition is good, but it covers a lot of complexity.
|Volcanoes come in all shapes and sizes. This is a maar (200 m across) that is inside a large caldera volcano (4000 m across), Askja in Iceland.|
|Pillow lavas form when lava erupts into water and are common at mid ocean ridges. Other underwater lava types include lobate and sheet flows. There are a lot of these lavas on Earth, they are just harder to go visit. National Oceanic & Atmospheric Administration (NOAA).|
|Lava flow on Mars looks a lot like lava flows on Earth, just with more impact craters. Mars Orbital Camera from NASA photojournal.|
|Lots of overlapping lava flows on the flanks of Olympus Mons. NASA Photojournal.|
|Lava flows on Venus look like lava flows on Earth, but can be 1000's of kilometers long (an order of magnitude bigger than our most impressive lava flows on Earth). Radar image from Magellan spacecraft, NASA photojournal.|
|Stacks of basaltic lava on the Moon exposed in an impact crater.|
|An artists rendering of the plumes from Enceladus with possible hydrothermal systems driving water from the subsurface ocean to the surface to form plumes. NASA photojournal more description here.|
|Salt flows in the Zagros Mountains, Iran are examples of extrusive salt tectonics on Earth. Scale bar is 10 miles. Image from GoogleEarth.|
|Ahuna Mons on Ceres appears to be endogenic (sourced from inside the planet). It is taller than Mt. Rainier, but not shaped like it... and is a good candidate for volcanism. Image credit NASA/JPL-Caltech/UCLA/MPS/DLR/IDA|
|Active volcanism in our solar system, a plume from Io, a moon of Jupiter. NASA photojournal.|