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Mt. Hood Meadows Shooting Star - Tree Strike

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#1 Nof

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Posted 07 December 2015 - 12:41 AM

On the night of Tuesday November 17, 2015 the windstorm that hit Oregon also hit Mt. Hood Meadows. Between 7:00 and 8:00 PM winds averaged 71 mph, with a top gust recorded on Cascade of 115.4 mph! During that timeframe two large living hemlock trees, measuring 24-to-32 inches DBH (tree diameter measured at 4.5 feet above the ground) and approximately 80-to-100 feet in height fell across both cables of the Shooting Star lift line, approximately 100 feet uphill of Tower 1.


Any thoughts?

#2 Mike12164

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Posted 07 December 2015 - 09:27 AM

Lot of factors here, could be as simple as cutting the trees and performing an inspection. However, as happened at Mt. Seymour in Vancouver, BC in 1998, trees on the line can pull several towers severely out of alignment. In the Mt. Seymour case the entire lift was a write-off.

Judging by that image though the weight is pressing down directly on the line and not really pulling to either side and trees didn't hit any towers or chairs so I doubt the damage is too severe, impossible to tell from a single image though.

#3 Kelly

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Posted 07 December 2015 - 12:11 PM

The Pacific Northwest brings a number of challenges for ropeway operation, this is a infrequent but not unheard of event. There are items briefly mention that are worth discussing in greater detail in these forums. The very dramatic photo itself can actually give clues to the event.
-Even though the haulrope looks skinny in this picture the breaking strength far exceeds any force that the tree could apply – haulrope safety factors far surpass any other component…well of just about anything that we humans use.
-Could the tree smoosh the haulrope where it is touching – again unlikely, wet Fir has the compression strength (force needed to dent the material) of 300 psi, haulrope is near 100,000 psi.
-How fast the tree fell is another indicator of potential damage; notice the limbs at the very top (buried in standing trees) are intact and no other limb debris is visible on the ground, this along with the rope still in the sheave grooves the chairs still attached and the comm line intact gives a good indicator this was a slow fall lessening severe impact damage.
-Prevention is a quick topic to jump to; it is difficult to manage the complete health of trees – notice the tree itself is structurally sound, all limbs in this case seem to be green. The failure is with the root system which is very difficult if not impossible to detect.
-As a side note: this resort has a very strong danger tree mitigation plan that actually is used by other resorts. Bad luck – yes.

Some off topic wire rope history…
Skilift cable (called haulrope or wirerope) has some interesting names associated with its strength. The term wirerope is an old carryover of the improvement of “stranded” manila rope.
Plow (Plough) steel, an original strength term, pertains to a higher grade of steel than mild steel used in the early 1800s in England. It contains a higher content of carbon than mild steel making it stronger but harder to work than mild steel. Origins of the name tend toward its use in farm plows. First shipments of higher grade of steel (plough steel) imported from England to North America are attributed to the John Deere company's need for improved steel for production of higher strength plows in the 1840s.
The names are descriptive of the improvement in strength – See image.
Attached File  Plow-stength-tabels.jpg (84.09K)
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A tremendous amount of testing has been done with wirerope – this image shows the European wirerope maker Fatzer’s plant with a test chairlift nearby.
Attached File  Fatzer-test-area.jpg (67.35K)
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History of Stranded Wire
Wire rope made from bronze was recently found in an excavation of Pompeii – ½" diameter – 3 strands - 15 wires per strand - 4.5 meters long – estimated date of manufacture – before 79 AD. Also another bronze rope was dated before 1 AD.
Attached File  1-BC.jpg (48.79K)
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Early and perhaps first use of stranded “iron” wire rope
The French Navy around 1810 replaces chain used for metallic conductors and adopts a 3 strand - 8 wires per strand – 1-1/8” diameter iron rope for a better conductor in the lightning protection system in wooden ships. Although not of load bearing, this is one of the first documented uses of multiwire stranded rope. Lightning protection is considered a big concern – not only does the crew get electrocuted, the mast will explode and what remains of the ship catches fire. The chain-to-wirerope evolution is repeated 20 years later for hoists in German mines.

#4 Nof

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Posted 10 December 2015 - 06:15 PM

Thanks for the replies! Typically the wind comes straight down the line on shooting star. This was always a factor when deciding to ride this one (bundle up!) I know they have had trees on the Hood river meadows lift before and it never seemed to knock it out of service for very long.

Perhaps they are worried about the tower or the footing for it. I would imagine some sheeves and bearings are going to need replacing, possibly the cross arms on tower 1 (edit: looks like they aready did the later).

This post has been edited by Nof: 10 December 2015 - 06:18 PM

#5 Nof

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Posted 12 December 2015 - 08:19 PM

Updated today: https://www.skihood....for-wind-damage

It would appear to me anyway the tower and footing was damaged to some extent. I don't really find this too shocking as that tower is sunk in a natural runoff ditch probably subject to being soaken wet most of the time. Enough force might have tweeked it some. They are saying it might re-open by Christmas telling me they are probably/possibly repouring concrete. Which at this time of year would require meticulous curing infastructure so that it does indeed cure.

#6 Kelly

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Posted 25 December 2015 - 04:46 AM

testing and evaluations have now been completed and the lift is now in service

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