Glacial History of Bristol, Vermont. – BRISTOL RECREATION CLUB

A Brief Backstory of Vermont’s Formation

The first transformation of Vermont was during the Cambrian time. During this period, present-day Burlington was not far from the equator, making Vermont and the sea that covered it, warm and tropical. During this time fish had not yet evolved, so the only creatures living on the ocean floors were trilobites and snails.

Geologists have discovered that over the last billion years, the continental plates have moved together twice, and apart twice, each time a new supercontinent was created and each would break apart. Vermont used to be on the continental edge. Because of this, Vermont endured two main impacts: Vermont’s bedrock is made up of sea sediments. And Vermont is vulnerable to continental movement.

Vermont is made up of sedimentary rocks and many of these rocks have gone through metamorphism. These rocks are then called metasedimentary rocks.

There have been four major mountain building events caused by continental movements. During these events, mountains were raised up, rocks were thrown over other rocks, and heat pressure caused existing rocks to metamorphosize which increased volcanic activity.

During the Precambrian collision, plates began to spread apart creating a rift zone. This caused the valley to widen and the Grenville Mountains began to erode. This caused sediments to be washed in and pile up on the valley floor. This created Vermont’s Iapetus ocean.

These rock depositions from the Iapetus see can be seen today in sandy beach sediments that are now quartzites, also known as metamorphosed sandstones, of the Bristol Cliffs and the White Rocks in the Green Mountains. The Bristol Cliffs were created by the Iapetus ocean during the Grenville Mountain event.

The Iapetus ocean paved the path for the deposition of Vermont’s rocks and sediments.

These rock depositions from the Iapetus see can be seen today in sandy beach sediments that are now quartzites, also known as metamorphosed sandstones, of the Bristol Cliffs and the White Rocks in the Green Mountains. The Bristol Cliffs were created by the Iapetus ocean during the Grenville Mountain event.

Vermont’s Glacial History

Earth entered the most recent glacial period, known as the Quaternary Glaciation, around 2.6 million years ago. During the Quaternary Glaciation, there have been twelve glacial periods, the most recent is known as the Ice Age.

The glacier that engulfed much of the U.S., including Vermont, stretched on the east coast extending as far as Long Island, NY, to the northern border of the U.S. The glaciers reached their full size 25,000 years ago. This was the beginning of climate change. Soon after, the glaciers began to retreat. The melt left behind formed large freshwater bodies of water in Vermont, including Lake Vermont. This lake filled the Champlain basin to 620’ in elevation.

The laurentide ice sheet retreated to the north and exposed the basin to the St. Lawrence seaway. This exposure allowed freshwater to drain out in a matter of hours and allowed saltwater to move in, creating the Champlain Sea. Around 10,000 years ago the Champlain Sea reverted to a freshwater body of water and Lake Champlain was created.

Bristol’s Glacial History and Geological Transformation

Topography of Bristol:

The forces of the tectonic plates created the foundations of the Green Mountains and the Champlain Valley. The glacial ice masses carved and refined Vermont’s geographical landscape to create Bristol’s landscape that we can see today. Bristol’s landscape consists of mountains and rivers to the east, and rolling hills and fields to the west. In the lowlands of Bristol there is fertile farmland that supports the local dairy farms.

Marine silts and clay deposits from the Champlain Sea provide agricultural soils that have benefited Bristol. In many areas, the glaciers have exposed the Cheshire quartzite bedrock which is resistant to erosion. These quartzites can be seen best on the western side of South Mountain and on the west and southern sides of Hogback Mountain, known as the Bristol Ledges and Deep Leap.

Soils and Surficial Material:

There are a variety of soils in Bristol due to the wide differences in terrain and the effects of glaciation. Bedrock on the ridgelines of Bristol was left exposed and a large amount of till was deposited, post glacial lakes and flooding are responsible for various clay and silts being deposited.

Around half of Bristol consists of the soil types of rock, very rocky complex, and extremely stony loams. This makes it hard to develop these areas because of the bedrock. In the north-south corridor located on the western side of Bristol there is a wide variety of soil types, including gravelly sand loams and loamy fine sands which are good soil conditions for development due to their permeability; stony, very fine sandy, and fine sand loams are also moderately suited for development. The areas that are best suited for development because they contain the proper soil environment border Monkton Road, Hardscrabble Road, Burpee Road, North Street and Vermont Route 116.

Mineral Resources:

The Kame terrace deposits consist of sand, cobble, and gravel. These were all deposited throughout the entire village of Bristol and they sit along the eastern spine of the Green Mountains during the glacial retreat.

Gravel is the main subsoil deposited throughout the village of Bristol. These gravel deposits are highly valued. Most of Bristol’s residential septic systems benefit from these gravel deposits because of the easy permeable soils that allow conventional septic systems.

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