Borah Peak Region
Idaho

Field Day 2, Stop 2

Susan Fakhrai-New Mexico
Ann Stevenson-New Mexico
Cathy Williamson-Louisiana
Marsha Willis-Texas

Heading Down the Highway

You are driving along the highway and see a strange white line in the landscape.

As you get closer, what do you observe?

This white line is actually a very long line made of sandy, rocky material where there is no plant life.


Meredith is almost 2 meters tall. You see her standing on the ground at the base of the white line. The ground at the top of the white line is about 0.75 meters above her head. It appears like this for a distance of 35 km.

What is going on here?

This white line is evidence that the land pulled apart and the crust in the foreground dropped about 2 meters and the crust on the opposite side rose 0.75 meters. This is called a fault scarp. It probably happened because of

A Whole Lot of Shaking Going On! On October 28, 1983 a large earthquake rocked the area around Challis, Idaho. A woman who was there saw the fault form “… just as though one took a paintbrush and painted a line along the hill.” In a second it raised on side of the hill and dropped the other side 3 feet.
(Quake Replay in the Great Basin, Natural History Magazine, June , 1986)

The quake measured 7.3 on the Richter Scale and caused two deaths and $12.5 billion in damages. Imagine how much higher these statistics would be if this quake occurred in a large urban area instead of this isolated area of Idaho.

Mercalli Intensity Scale

The Borah Peak Earthquake was rated a IX-X on the Mercalli Intensity Scale. This scale measures the effect of the earthquakes on humans and their man made environment. Another eyewitness stated they saw trees whipping back and forth almost touching the ground. The scale ranges from I –XII.

–Level I- People do not feel the earth move.
–Level VII- People have difficulty standing.
–Level XII- Almost everything is destroyed.

Other Geological Features

A syncline is formed with compressional forces. It is a large fold whose limbs are higher than its center and the youngest rocks are in the center.

Possible Connections to Mars

Are there quakes on Mars? What features on Mars look similar to the fault scarp you see at Borah Peak? For images of Mars, visit http://www.msss.com/mars_images/

Good Photos of Borah Peak

Visit
http://www.idahogeology.org/fieldworkshps/borahpeak95/default.htm