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  • MOUNT BAKER: Eruptive history, hazards, research.

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    This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.
    Northwest Geology Field Trips, by Dave Tucker, is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 United States License. You can use what you find here, repost it with attribution to the author, "remix" it for your own purposes, but may not use it with the intent of making money off of it.

    EDUCATORS: Please feel free to use anything you find here that is useful to your mission educating people about Earth science. E-mail me if it would help to have a larger or higher-resolution version of any of the images. tuckerd at geol dot wwu dot edu

Baker River geology field guide posted

Baker River's braided channel just above Lake Creek.

Baker River’s braided channel just above Lake Creek.

After a hike up the Baker River Trail at the north end of the Baker Reservoir, I just had to write it up for the blog. Shuksan Greenschist, waterfalls, an entrenched delta-cum-alluvial fan, exhumed eroded giant tree stumps, and really cool river cobbles, including volcanic breccia from Hannegan caldera. An easy round trip of 5 miles, even good in the pouring rain. Read the field trip here.

Online geology field trip: the Deadhorse Volcano, Skyline Divide, Mount Baker volcanic field

The last couple of miles of Skyline Divide. The Deadhorse Volcano is marked by the red pin and Hildreth’s unit designation ‘acr’. Click to enlarge.

A nearly unknown volcanic vent is exposed in cross section on a rock wall at the south end of Skyline Divide north of Mount Baker. Click here to read my on-line field guide to the informally named  “Deadhorse Volcano“. Yes, I know, winter approacheth, so chances to visit this eroded volcano are fast-slipping away. Hope for a weather break, or save this little gem until after the snow is gone next year. The snow that hasn’t fallen- yet.

Martha Lake erratic is all cleaned up!

Greg shows off the cleaned-up Martha Lake erratic. Spic and span! photo courtesy of Greg Kulseth. Click to enlarge.

Greg Kulseth reports this morning that the graffiti has been removed from the Martha Lake Erratic at Martha Lake Airport Park. The Snohomish County Parks Department also put up an interpretive sign about erratics: where they come from, how they get swept up into glaciers, and the extent of the last glacial maximum. The sign mentions the Lake Steven’s Erratic, and states that it may be the largest in the US.
Special thanks to David McConnell of the Parks Department, who, last I heard, was going to spearhead the cleanup, and to Greg for sending the good news.
I’ve updated the Martha Lake erratic webpage to show the now-cleaned up boulder.
Looking at my calendar, I see it is ‘Spring’. Looking out my window- hmmm. Oh, there’s a new snowdrop blooming, and maybe a leaf bud! Guess the calendar isn’t that far off, and the precession of the equinox marches on.

Have a good spring!
DT

Coupeville’s Big Rock in the news

Big Rock. Island County Commissioner Angie Homola and her daughter Kira. Angie says she is 5 ft tall, so the erratic is about 22' (6.7 m) tall. 2010 photo by Dave Tucker.

Big Rock in the 1960s. Photo courtesy of Donn Charnley.

The big rounded erratic in Coupeville has recently been the subject of debate. The town council considered a proposal to purchase the land the erratic sits on to protect the rock from possible destruction. Their was concern that the owner of the apartments behind (to the west) of the rock would consider ‘removing’ the boulder to make room for a new and larger apartment complex. Here is the story in the Whidbey News Times. An earlier article in the paper, including information from UW glacial geologist Terry Swanson, describes the rock and the property ownership issue. The second article also reveals that at least as late as the 1930s, a stairway allowed access to the rock’s summit. Note that the newspaper refers to the big hunk o’ greenstone as ‘granite’, though a much earlier story in a rival newspaper (South Whidbey Record), identified the rock correctly in an article about erratics featuring Terry Swanson.

The Wedgwood erratic is on a lot cared for by the neighborhood.

Thanks to Valarie Bunn of Seattle’s Wedgwood neighborhood for supplying these links. She wrote about the similar Wedgwood erratic in her Wedgwood history blog.

Thin en echelon dikes in the Highline Community College erratic; AND a National Geo ‘erratics’ article

The granitic erratic at Highline Community College. Photo by Bud Hardwick.

Bud Hardwick sent photos and geographic information about a large granitic erratic (yes, another one of those dang things) at Shoreline Community College in Des Moines (Washington!). I looked closely at his photos and made some deductions about the geology. Take the virtual field trip to this erratic elsewhere on this website. The rock is notable because of the textbook en echelon dikes running the full length of the big erratic.

Also, the latest National Geographic has a photo essay on glacial erratics by Fritz Hoffman. Alas, none of the ones describe n this website or any others in western Washington are included, not even the Lake Stevens Monster, the largest in the whole country. See  the photos here (an NPR website).

Erratics on the beach at Seattle’s Discovery Park

The largest of several erratics on the north shore of Seattle's Discovery Park. Photo provided by Sandy Bowman.

A new field trip to visit some erratics on the north shore of Discovery Park is here. These were measured and photographed by Sandy Bowman and Consuela Larrabee. I confess I’ve been sitting on this report for months and months. This trip requires a hike on the North Beach Trail, and provides a nice excuse to get outside for a partial day’s outing.

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.”

Victoria’s waterfront geology, Part 1: Harling Point

Harling Point, The Harpoon Erratic, and Migmatite Bedrock

The Harling Point erratic. This is a panoramio photo on Google Earth by crobinso2010. http://www.panoramio.com/photo/56782186

Bud Hardwick of Bellingham sent us a report on geology (and the Chinese cemetery) at Harling Point on Vancouver Island, in the Victoria-Oak Bay area. Read it here. The trip features a landmark erratic, and migmatite bedrock. This is the first in a pair of articles Bud sent. The next will be to Songhees Point on the west shore of Victoria Harbor. Stay tuned, it will appear on Northwest Geology Field Trips later this week I hope.

A portion of the Chinese cemetery at Harling Point. There may be as many as 1000 burials here. Bud Hardwick photo.

Beach erratic in Des Moines (the one in Washington, not Iowa!)

Last spring I put out a call for intrepid readers to investigate a reported Jackass conglomerate erratic on the beach at Des Moines, between Burien and Federal Way. Thanks to Sandy Bowman and Bud Hardwick for independently investigating. Turns out the large rock is granitic, not conglomerate. Read the article.

Consuelo Larrabee at the Des Moines erratic. Photo by Sandy Bowman.

By the way, does anyone know how I can share Google Earth .kmz files on this website? If you do, contact me via email with instructions:

email address to send reports and photos. I'll credit you.

Virtual field trip to Raptor Ridge geology posted

Looking south from Raptor Ridge. Two unrelated types of eroded grooves cut deeply into the soft sandstone. Click to enlarge.

I’m thankful to the forces of nature that present us with such a wealth of fine places to see geology and the scenery that goes with it. In that spirit, I wrote a guide to geology on the hike to Raptor Ridge in the Chuckanut Mountains, south of Bellingham. There are some rock cliffs, two different styles of eroded grooves eroded in the rock, two erratics, a water fall, and pervasively weathered Chuckanut sandstone. All this is capped with a fine view at the top. Click here to read the guide. It is a nice winter hike, unless there is too much snow. But then, it becomes a really great cross-country ski trip! Just the thing, either way to work off some Thanksgiving over eating. See you on the trail!

Dave