1Hi, it's Doug.
2What counts as a mountain?
3Would you call this a mountain or just a hill?
4For me, growing up, I thought of this as a mountain.
5But that's probably because I grew up in northern Illinois, one of the flattest places in the world.
6And this thing... this hill, I guess, is one of the tallest things around.
7Turns out the only reason it's there is because it's the old landfill.
8It's a hill made out of garbage.
9Someone named Sophia has a question about actual mountains.
10Let's give her a call now.
11Hi, Doug.
12Hi, Sophia.
13I have a question for you.
14Could a mountain turn into a volcano?
15Oh, that's a great question.
16Could a mountain turn into a volcano?
17If you're thinking, "No way," here's a true story that might change your mind.
18Heimay is a little island just off the coast of the country of Iceland.
19A few thousand people live there and call it home.
20The island of Heimay is actually a mountain.
21If you were to sail up close to it, it may look more like a hill from the side.
22But when you include all the part of it that's under the ocean,
23you can see that the part sticking out of the water is the top of the mountain.
24One day in the year 1973,
25the people living on Heimay got the surprise of their lives.
26A crack had formed on one side of the island.
27Lava was spurting out.
28The residents of the island were evacuated to safety on nearby Iceland.
29The eruption lasted for nearly six months.
30Finally, the lava cooled off and had become solid rock.
31Volcanic rock called basalt, rock that's dark in color and extremely tough.
32The island of Heimay had gotten bigger.
33So it seems like here's a case where a mountain did turn into a volcano,
34at least for a few months.
35Now, to be fair, I didn't tell you much about the original part of Heimay,
36the part people had been living on.
37It's made of basalt too.
38Technically, Heimay had always been a volcano.
39It's just that it hadn't erupted in a very long time,
40and so the people of Heimay were a little surprised.
41But it does make you wonder.
42Could any old mountain suddenly turn into a volcano and start erupting lava?
43I live in the U.S. state of California,
44just a few hours south of the state of Oregon and Washington.
45And anytime I drive around in any of these places,
46I'm always amazed at how many of the mountains here are actually volcanoes.
47Quiet, peaceful-looking Mount Lassen in northern California
48It erupted a hundred years ago, back in 1915.
49Beautiful Mount St. Helens in Washington,
50it blew off half its top back in 1980.
51And it's the same thing for so many other mountains in this area.
52Mount Rainier, which towers above the city of Seattle, it's a volcano.
53Mount Hood in Oregon, volcano.
54Even little mountains like this one, called Black Butte,
55along the side of the road in northern California, it's a volcano.
56When you see so many mountains that are volcanoes,
57it gets tempting to think, "Well, is every mountain a volcano?"
58How do we even find out?
59Like, would you just have to wait for it to erupt lava to find out?
60But surely not.
61Let's say there's a mountain near where you live.
62What do you think?
63How could you find out if it's a volcano?
64What are some clues you could look for?
65You might have had different ideas.
66Maybe you thought to feel it, see if it feels hot.
67Here's another possibility.
68Look at what kind of rock the mountain is made of.
69If it's volcanic rock,
70then there's at least some chance that the mountain might have the ability to erupt lava.
71You can get good at learning what volcanic rock looks like.
72I mentioned basalt earlier.
73It's one of the most common kinds of rocks that volcanoes are made of.
74It's always dark in color and really tough.
75This is rock that doesn't crumble easily.
76Some basalt even has little holes in it, like this.
77Those are air bubbles from when it was still lava.
78If you go out and look at what kind of rock different mountains are made of,
79you'll discover for yourself that not all mountains are made of volcanic rock.
80For example, check out the red rocks of Colorado's Front Range,
81the east edge of the Rocky Mountains.
82They're made of a reddish-colored sand and bits of pebbles
83that formed along the bottom of a river.
84Or even Mount Everest in Asia, the tallest mountain in the world.
85Now, if there's any mountain that might be a huge volcano,
86it's tempting to think, "This has to be it."
87But climbers who've made it all the way to the top
88can tell you that a lot of the rock up there contains fossils of animals that lived along the bottom of the ocean.
89Up on top of Mount Everest, there's rock made of sand, pebbles, coral even.
90There's no volcanic rock at all.
91Mount Everest has never erupted,
92and there's no reason to think it ever would.
93It's not volcanic.
94Still, you might be surprised to find some mountains made of volcanic rock,
95even if you live somewhere that's not ever been known for having volcanoes.
96Like here in the U.S. state of Missouri, for example.
97Thousands of miles from any famous volcanoes are the St. Francis Mountains.
98The tallest peak, called Taum Sauk, was a volcano that spewed out lava,
99which cooled off and became volcanic rock.
100Or in the U.S. state of Virginia are two small mountains.
101Maybe we should just call these hills,
102but both of them are made of basalt.
103Where did that come from?
104Not every volcano is an active volcano.
105All of these examples are extinct volcanoes,
106volcanoes that erupted an extremely long time ago
107and so, left behind volcanic rock
108but which haven't erupted since
109and scientists think are really unlikely to erupt again.
110So in summary, most mountains won't just erupt lava out of nowhere.
111If they do, it's usually because there have been eruptions in the past.
112While not every mountain is a volcano, a lot of them are,
113sometimes extinct volcanoes of the past.
114You can look for clues by searching for volcanic rock.
115That's all for this week's question.
116Thanks, Sophia, for asking it.