We use cookies to improve your experience, some are essential for the operation of this site.

Close up lava type comparison.

Close up lava type comparison.
Close up lava type comparison.
Close up lava type comparison.
Close up lava type comparison.
Comments (0)
Linder, Christopher L.
Close up lava type comparison.
Still Image
Here are two lava close-ups: pahoehoe (left) and 'a'a (right). Both types can form from the same molten lava. In this case both rocks are basalt, a mixture of mostly silica and oxygen, with substantial amounts of magnesium, calcium, iron, and aluminum. The pahoehoe is riddled with perfectly round bubbles that show where trapped gas was trying to escape from the rock as it cooled. Near the edge of the rock (top), the bubbles are smaller because the rock quickly hardened in the cool air. Nearer the middle, the rock stayed hot longer, and the bubbles are larger. The 'a'a (right) was much more sticky. Its top surface is spiky where chunks tore away as it hardened. Inside, the rock was too stiff to allow round bubbles to form - the ones that did form are elongated like soda bubbles squeezing around ice cubes in a glass. They've been caught in mid-movement as they rose toward the surface.
Image of The Day caption:
Two types of lava can form from the same volcano. These samples came from an eruption in Antarctica that occurred about 25,000 years ago. They were collected by WHOI geoscientists Adam Soule and Mark Kurz and Joint Program student Andrea Burke during a Polar Discovery expedition in 2007.The kind of lava on the left is called pahoehoe (rhymes with ?joey-joey?). It is smooth on the surface. Inside, it is riddled with round bubbles formed by trapped gas that was trying to escape the molten lava. Bubbles near the surface are small because the rock cooled quickly there. Deeper down, the rock stayed hot longer and the bubbles grew bigger. The kind on the right is called `a?a (?Ah! Ah!? as you might say if you tried to walk on it barefoot). It is spiky on the surface. Inside, the hot lava was so stiff that few bubbles could form.
Photo by Chris Linder
© Woods Hole Oceanographic Institution
This item includes these files