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NY Iron Mines Exploration

March 19 2015
Just north of New York City, in the hills of Harriman State Park, are a collection of mine workings from the 18th and 19th centuries. Some were worked into the 20th century, but most were abandonded much earlier. These miners dug out hematite and magnetite using a combination of hand tools and black powder. Some of the workings are open trenches, some are vertical shafts and some slope into the hillside. All are flooded with water. There are several guides and books that describe the mines and their history, but I have seen and read nothing about the interior of the flooded mines. This project aims to address that by sending an underwater ROV into the flooded mine shafts to explore and document the excavations.

March 19 2015


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Mission Underway

The mine opening is well lit and we were able to setup right at the waters edge. The water is very black and you can not see the bottom even in the first few feet. We quickly determined that it is about 2 meters deep just a couple of meters from the waters edge. You can see that the mine tunnel on the right is not flooded all the way to the roof. The pillar at the front of the mine is repeated inside, so that two tunnels go into the mountain, one on the right and one on the left. The question is, how far does the tunnel go in?

The weather was very good with temperatures of 28C and clear skies. There was little wind. The water was about 14C according to the ROV.

First step was to setup the tether. I did not want it to drag on the rocks on the bottom of the shaft, so I added fishing floats every three meters. This made it slightly buoyant, with some droop between the floats.

The dive started well but visibility in the water was terrible. You can see that in the video. With the lights on low we could see almost nothing, with the lights on high we could see less. It had rained quite hard the previous day, so that may have accounted for a build up in sediment. Part of the problem was reflections inside the main tube. The light spills across the image. I think that can be improved back in the lab.

There are some surprises in the video. Something lives in the mine. We saw salamanders near the entrance, but what is it that we see in the video? Suggestions welcome.

With almost no visibility it was hard to navigate in the shaft. The compass on the ROV misbehaved and did not read north. At least it did not match the compass I had brought. Perhaps all the iron in the walls was causing an issue? We tried to explore slowly, but with little visibility we managed to wrap the ROV around one of the rock pillars. Essentially we drove in in one entrance to the mine and emerged out of another. We tried repeatedly, but somehow we could not follow the same path back. Perhaps the ROV had slipped through a small opening.

Pulling on the tether had no effect. It was stuck, probably on one of the floats.

The ROV was about 4 or 5 meters into the mine and about a meter below the surface. It could make no further progress towards us. So someone had to go swimming. That would be meet.

The water was cold enough to force the breath out of my lungs. Luckily I was quickly to the ROV, where the water was about 2 meters deep or more and I had to swim. I cut the tether under the water with the scissors on my Swiss army pen knife and quickly returned. Luckily 28C weather quickly warms you back up.

With the ROV disconnected we managed to pull the tether back out and even retrieved all of the floats, but there was no way to reattach it in the field, so we packed up and hiked out.

How deep was the mine? We don't know. It looks like a scoop that goes 2-3 meters past the rock pillar and then returns on the other side. But it could be deeper, we did not manage to map it or finalize its shape. We need to return when it has not rained and with a better tether and lights.


Thanks for sharing your video Chris! I have no idea what that little creature was that flew past, but you should definitely investigate further.

As far as the lighting situation, you might want to try experimenting with some external lights. That will most likely clear up your tube.

@Kevin_K: I agree, so external lights is next on my list of things to experiment with. If you have any suggestions let me know. I'm fine working with high power LEDs, but I am unsure how best to waterproof them. Do they need to be behind a plastic lens, or can they be exposed to the water, for example?

If you're operating purely in freshwater, you can probably get away with having them exposed. I operate in saltwater, so everything I do needs to be sealed. I haven't done enough research to make a decision yet for mine.

I also know the OpenROV team is working on a set of external lights for their experimental section, but I'm unsure what stage of development they are in. They are sealed for saltwater use.

Preparation Stage

The Iron Mines project has shifted from preparation into execution of the mission with our first visit to a mine. This was still very exploratory in nature, but it was fun.

The Dater mine is just north of New York City and was one of the first mines we visited when we were planning the project. It is a short hike over rough terrain to the mine, which consists of a large opening with a central column. The shaft is at 920 feet above sea level and proceeds into the mountainside with a slightly descending angle. It is flooded. The area around the mine is strewn with iron ore tailings.


I put the Greenwood Explorer in the water for the first time. You can see from the short video that there was not much to see. This test used the laptop in bright conditions, confirmed the ballast, worked out how to make the tether neutrally buoyant, and showed me how easy the ROV is to control or not.

I used a Think Tank pixel sunscreen to shade the laptop and that worked well. I could see the screen in full sun.

Initially I was moved off the rocks by the parks police, but they said sitting on the beach was fine. It was harder to launch from there, but otherwise OK.

The ballast was fine. I had added zinc washers on the front rod until it was neural in tap water. It was then slightly buoyant in the estuary.

I tried several fishing floats on the tether and my largest size, 2.5cm (1") seemed to work best, placed every 3-5 meters. More testing will be needed to confirm this though. It's very hard to see what is going on. I'm going to need to keep the cable from getting snagged in the rocks of a mine shaft, so this is important.

The water had almost zero visibility, but it served as a decent test. I can confirm that waves from boats are a real issue and I was worried the ROV would be damaged. It's a stony beach with fair sized jagged rocks at the waters edge.

The East river's current was strong, so I never managed to drive the ROV more than about 20 meters offshore, it just got pulled away by the current and swung back towards the bank.

I found the ROV hard to control. Perhaps the current, waves and drag from the cable along the beach did not help. Perhaps I just need more practice.

All in all a very successful test.


The "pixel sunscreen" you linked to is amazing! I often run into glare problems when deploying my ROV, and this looks like a great solution. Have you flown the ROV anywhere else recently? Thanks!

The pixel sunscreen is amazing and I can highly recommend it. It works well anytime you need to use the laptop outside.

Life has been unusually busy, so I have not made further progress, but I am hoping to do another dive soon.

Good news. The ROV is built. Initial testing in the workshop has been good and all systems seem to be operational. The next step is to test the ROV in water. It's still quite cold outside in the North East of the US, so this may be a brief test in the East River of New York City.

Assuming the test dive goes well, the next step will be at one of the mine sites. I have been considering what the best mine to visit will be. I have come up with the following criteria:

A. We want them to be hikable as a day trip with plenty of time at the mine.

B. Mines that are a little be less accessible will mean a quiet visit without "tourists". That may seem like the opposite approach, as we want to share this with others, but mine shafts and the area around mines are very dangerous. We don't want to lure people to the edge of a deep dark pit.

C. Clearly we want flooded mines. So I have made a list of all of the flooded excavations listed in Iron Mine Trails -

D. Some mine sites have one excavation and some have several. If we carry in all of the equipment and it turns out that our shaft only extends 3 meters into the hillside, then it may feel like a wasted day. So perhaps we prioritize sites that have multiple options.

In addition, the mine workings come in four types: 1. Vertical shafts 2. Shafts that slant into the hillside 3. Horizontal shafts or shafts that slope up 4. Open cuttings

Type 3 are not water filled, so we focus on the other three. Type 1 may be best explored with a camera on a rope initially - perhaps a GoPro with a dive housing and some lights. Type 2 are the most tantalizing and the Dater mine is of this kind - the mine that first inspired this project. Type 4 - open cuttings - may be the easiest, but they may be the most uninteresting. They are more likely to be filled with modern trash and may not be that deep. That said, one water filled cutting is rumored to be over 100 feet deep, so that will be worth exploring.

I'm crunching all of these parameters in a spreadsheet and coming up with a list of priorities. More to come as I decide which sites to explore first...


Congrats on the build! The ROV looks great! Interesting on the site classifications too.

What a great use for the ROV! Can't wait to see what you find!

Expedition Background

Mining technology in the 18th and early 19th century was primitive by today's standards. Holes were drilled by hand and then packed with black powder. The resulting rock, either the overburden that sits over the valuable ore or the ore itself then had to be hauled out of the mine.

Mules and horses provided power. Sometimes water power was harnessed and later steam engines helped de-water mines, haul loads and miners.

An active mine is constantly pumped to remove ground water, runoff and rain. An inactive mine quickly fills and is inaccessible. A mine in New Jersey was reopened during the second world war and the pumps ran for 7 months before mining could restart.

What did the miners leave behind in the mines, if anything? How deep are the shafts and passages? Are they a single tunnel that follows a vein of rock, or do they branch? We can only answer this if we descend below the surface of the water.

Diving in mines is dangerous, but sending an ROV in has little hazard other than potential financial loss if the ROV becomes stuck, entangled or fails.

Several candidate mines are being considered. And the ROV is now under construction based on the V2.7 kit from The date of the first dive is still to be established.


Wow, looks like a great expedition you'll have here! It's definitely a better idea to use the ROV in these tight and dangerous spaces. Be sure to take plenty of pictures and stay safe!