How the Three Sisters were made?

Question

How were the three sisters made? I know they are formed by erosion but I need more info.

Thanks for your time and help :)

Answer 1

I assume that you mean the Three Sisters in the blue mountains, NSW, because you asked a similar question a couple of days ago; and not the thress sisters volcanoes of Oregon.

Here's a Wikipedia reference that gives a brief, but good description:

http://en.wikipedia.org/wiki/Three_Siste...

Here's a second reference; explaining that they were formed from erosion along two sets of intersecting joints:

http://www.amonline.net.au/geoscience/ea...

There used to be some enjoyable rock climbs on the three sisters; but climbing on them is now banned.

Answer 2

From USGS:

"Three Sisters is one of three potentially active volcanic centers that lie close to rapidly growing communities and resort areas in Central Oregon. Two types of volcanoes exist in the Three Sisters region and each poses distinct hazards to people and property. South Sister, Middle Sister, and Broken Top, major composite volcanoes clustered near the center of the region, have erupted repeatedly over tens of thousands of years and may erupt explosively in the future. In contrast, mafic volcanoes, which range from small cinder cones to large shield volcanoes like North Sister and Belknap Crater, are typically short-lived (weeks to centuries) and erupt less explosively than do composite volcanoes. Hundreds of mafic volcanoes scattered through the Three Sisters region are part of a much longer zone along the High Cascades of Oregon in which birth of new mafic volcanoes is possible."

From Jefferson County, CO:

"The dominant features of this Open Space park are the rock outcroppings known as "The Three Sisters" and "The Brother". The outcrops are metamorphic rock of the Precambrian Era which consist largely of silver plume quartz."