16:23 Mon Aug 10, 2020
A Brief Geologic History of The Whites
After hearing word of a North Carolina earthquake that occurred this past Sunday I was reminded of my second passion, Geology. I started diving into the “shakemap” from the USGS website and was able to see where the earthquake was felt and read some reports of first hand experiences from this 5.1 magnitude earthquake. I found myself asking the questions of “Does North Carolina have a geological reason for having earthquakes?”, “How was North Carolina geologically formed?”. These questions inevitably lead to “How was Mount Washington formed?”.
Thanks to a paper written by R. Buchwaldt and F. Dudas I was able to dive into the evolution of Mount Washington and some geologic forcing that developed our beloved Appalachian Mountains. Below I will summarize some of the key elements to how Mount Washington came to be.
As the supercontinent Pangea formed, there were many collisions of other plates that molded the geology of the Whites. About 450 to 250 millions of years ago (Ma), the continent called Gondwana (Current day Europe and Africa combined) crashed into North America. During this collision, some of the Earth was thrusted upward causing a large elevated region. While the Appalachian Mountains at one point rose more than 4.5 miles high, forces of erosion weathered it down. There was a second collision of continents about 400 Ma between North America and a micro continent f Avalonia. The rocks were crushed together with a series of folding and faulting. Under the intense heat and pressure of this event, many of the sedimentary minerals of the earth were transitioned into different minerals through the process of metamorphism. Some of the infamous granite of the granite state was produced in this event where the heat and pressure was so strong that it melted the previous rock into granite.
A secondary type of geologic event that is responsible for most of the features we see today is glaciers. Approximately 0.08 Ma or 80,000 years ago the Wisconsinan glaciation occurred. It is estimated that back then there was an estimated 1km thick of ice on top of Mount Washington. “The deposited sediments have been dated by the Carbon method and indicate that the local ice had retreated from the lower elevations by 13,500 years and that the Presidential Range was ice free by about 11,500 years ago” said Buchwaldt and Dudas. Glaciers tend to hold onto and “eat up” rocks as they move. So, as they melt and recede they will leave behind some of their deposits in their wake. The White Mountains attribute some of their features to this process.
I found this paper very informative and fascinating. I have always wondered how Mount Washington came to be and now many of my questions have been answered! I hope you have learned some new geology about how our beloved white mountains were formed over time!
Information from R. Buchwaldt and F. Dudas paper titled: DEAPS 2013: Geology of the Mt. Washington area, New Hampshire, a glimpse into the evolution of the Appalachian Mountains
Nicole Tallman, Weather Observer/Education Specialist