Size matters: two giant erratics: Lake Stevens Monster vs Madison Boulder

By Dave Tucker

A request for assistance is highlighted below in red.

The Lake Stevens Monster's high side. Keith Kemplin (top) and Bob Mooers for scale. Full width can not be appreciated in this view. Click to enlarge.

I have previously stated that the Lake Stevens erratic (“Lake Stevens Monster”) may be the largest in the USA, larger than the apparent reigning champ, the granitic Madison Boulder, near the town of Madison in New Hampshire. According to a brochure by the New Hampshire Division of Parks and Recreation, this is the “(l)argest known glacial erratic in North America and a National Natural Landmark”.

Looking across a portion of the 54' width on top of the Monster. Click to enlarge.

The Lake Stevens erratic was measured this past summer by Craig Valvick and Matt McCourt. However, an additional measurement, width, was needed to allow better comparison with the Madison erratic. This has now been made, and the comparison follows.

“Lake Stevens Monster” (serpentinized greenstone) 78 feet (23.77 m) in length 34 feet (10.36 m) tall and 54 feet (16.46 m) in width (widest point). The circumference is 210 feet (64 m). No mass has yet been calculated.

8th graders at the Madison Boulder.

“Madison Boulder” (granitic, no further detail known) 83 feet (25 m) in length, 23 feet (7.0 m) tall, and 37 feet (11 m) in width. No circumference is available, but assuming it is a square as it looks, this would be around 240 feet (length x 2 + width x 2). It weighs upwards of 5,000 tons.

Given the small difference in length (78 vs 83 feet) the large difference in height (34 vs 23 feet), and the large difference in width (54 vs 37), the Lake Stevens erratic is bigger, and is the largest measured erratic in the USA known to me. Further, while the base of Madison Boulder is reportedly buried “probably by a depth of ten to twelve feet” (see below), there is little doubt that at least a similar amount of the Lake Stevens erratic is buried. No mass has been calculated for the visible, above ground portion of “The Monster”. A 12-inch-wide chunk that had fallen off will be used to calculate density via weight and displacement of a volume of water. Once a rough volume for the entire erratic is calculated, mass can be estimated. Volume will be a tough nut, given the extremely irregular dimensions. Suggestions for a method of doing this are requested. Lake Stevens is smaller than the quartzite Okotoks erratic in Alberta (near Calgary), the accepted record holder for North America, but not by that much, really.

Does anyone have suggestions for how to measure volume of the “Monster”? It has an irregular shape. Would ground-based LiDAR do the job? How deeply buried is it? Would ground-penetrating radar be a tool to determine this?

The Wikipedia webpage for Madison, New Hampshire says: “The town is home to the Madison Boulder (43°55′52″N 71°10′04″W), the largest known glacial erratic in New England, and among the largest in the world. Madison Boulder is a huge granite rock measuring 83 feet (25 m) in length, 23 feet (7.0 m) in height above the ground, and 37 feet (11 m) in width. It weighs upwards of 5,000 tons. A part of this roughly rectangular block is buried, probably to a depth of ten to twelve feet. It is located at a state park in the northwest part of town.”


7 Responses

  1. Seems that someone clever with ground based Lidar could figure this out but relaince on assumptions about depth of burial would still be required.
    That said I think I need to block off some time when I next go anywhere near Grand Coulee. I think there may be two that exceed the Monster.

  2. I think Dan is on the right track. Perhaps something simpler, like a laser range finder used for measuring stockpile volumes.

  3. […] Greenstone is a low-grade, metamorphosed sea floor basalt. Another page on this website describes the rock in more detail, and compares it with the previous […]

  4. Im not sure if it is is as big as this one which is only 13 miles to the South in Monroe.

  5. Tucker neglects to mention where the Lake Stevens erratic is located!

    • Actually, I do. Location is in the earlier blog posts dealing with the Lake Stevens erratic- see the ‘related posts’ links at the bottom of the page. I also give full directions in my book, “Geology Underfoot in Western Washington”. See tab at top of this website page, or visit

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