Here's a link to an article from RR trade magazine RT&S (apparently written by the editor in chief) entitled "Severe drought may have caused track collapse in Maryland" that really discusses the Mass Coastal's RoW collapse near Sandwich< MA. Excerpt:
A 300-ft portion of rail, which dates back to the 1800s, dropped into a nearby pond. A locomotive was approaching the site when the accident happened, and was able to stop well before the damaged area. According to a preliminary report by Jacobs Engineering, the collapse along the south side of Lily Pond covered the length of approximately 300 ft and was about 70 ft to 90 ft wide at the base. The estimated height of the embankment lost due to the collapse was about 30 ft. Approximately 15,000 cu yd of material was displaced during the failure.https://www.rtands.com/track-maintenanc ... -maryland/
Jacobs was hired to look at the damage to Lily Pond, which is adjacent to the pond where the failure took place. The engineering firm does not know the cause of the failure.