Digital Varves

Varves of the Month for 3/1/2012 - 7/1/2012

Connecticut Valley Varves at Westmoreland, NH

Scale bar in cm.

Click on image to download original image file

This month's image is an image stitched together from smaller high-resolution images of varves collected in cores at Westmoreland, NH (ALD – Aldrich Brook site). Each varve is labeled with its annual number in the new North American Varve Chronology (NAVC). The varves show a very rapid transition from relatively thin to relatively thick varves up section. This transition (red line on varve image), which occurred at about 14,600 yr BP (after NAVC--AM varve year 6228 on the image), represents the end of a cold interval in which end moraines were deposited near Charlestown, NH. The following warm interval was marked by very rapid ice recession from Charlestown to northern New Hampshire and Vermont for about 600 years at a rate of ~300 m/yr. This period was one of very rapid melting and meltwater delivery to Lake Hitchcock in the Connecticut Valley. This resulted in the deposition of varves with a thickness averaging about 3X greater than during the previous cool interval.

A correlation of the varve records from Antevs' (1922) chronology (LCB57-63) and Westmoreland, NH (ALD site) along with their 9-yr running averages. The yellow region is the span of time shown in the varve image. The blue arrows represent dips in meltwater delivery (thinner average varve thickness) that correspond to periods of end moraine building near Charlestown, NH. The red arrow represents the rapid transition from cold to warm conditions following end moraine building.

Past Varves of the Month...