Wednesday, August 5, 2009
Columns of the Giants
Two layers in the lava may be clues to separate volcanic eruptions.
The First Flow
The straight columns formed as the lava cooled evenly under ideal conditions. They cooled from the top down and the ground upward.
The Second Flow
The twisted upper layer could have formed when a second eruption flowed over the already cooled first layer. The second layer could have pooled against a natural barrier that has since eroded. It probably formed under less uniform conditions, causing uneven fracturing.
How Columns Form
Perfect Conditions Make Perfect Columns
Hot lava, like most liquids, shrinks as it cools, causing tension in the new rock. The stress is relieved by cracking. The cracks often have three arms that spread at 120 degree angles, like the surface of drying mud.
Vertical columns occur only where lava of uniform composition and thickness cools evenly from top to bottom. These perfect conditions created the Columns of the Giants, one of the world's most intriguing wonders.
CLUES TO THE PAST
Signs of a Vanished Glacier
Ancient glaciers polished the tops of these columns, leaving behind their scrape marks.
The Power of Ice Crystals
The mounds of rocks at the base of the columns are called "talus." As water seeps into the cracks in the rock and freezes, the expanding ice crystals slowly wedge the massive blocks apart. As they separate, they fall into the heaps you see here.
Hidden Ice Field
You can feel cool air rising through the talus. Several thousand years ago an ice field forms here. This is what geologists call "the little ice age." Remnants of this ancient ice still remain, covered and preserved by the fallen rock.
Here is my mom sitting in the fallen rock to show you how much and how big it actually is.
Now... to walk back.
giggle~ no more "nature pics" of the walk...
I promise! The walk is over.