Lava flow trail stop 4Squeeze-ups
As you walk along the trail you'll notice gaping fractures in the rough basalt surface. Look between the rough walls of the fracture and you'll see one of Bonito Lava Flow's really cool squeeze-ups! Why are they called 'squeeze-ups'? Follow along to find out. Remember that Bonito Lava Flow was once just that - a flowing river of glowing hot lava. | |||
The top of the lava flow was exposed to cold air, so it began to cool and solidify first. The core of the lava river continued to flow while the top of the flow formed a rocky basalt roof.
Just like many other materials, rock shrinks as it cools off. As the solid basalt cap began to shrink, gaping fractures formed, pulling the sides apart. In some places, hot, semi-solid basalt lava was able to squeeze up through the fracture. The semi-solid lava is very plastic, like modeling clay or ®silly putty. As the lava oozed up, it scraped the jagged, solid sides, creating grooves in the plastic-like mass and, voilà, a squeeze-up was born!
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 Click
here to see another great squeeze-up. |
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