Tracy Arm-Ford’s Terror Wilderness Area, Alaska
Seventy thousand years ago, the earth was cooling off. As more of the earth was covered in snow, it reflected more sunlight out to space, producing further cooling in a reinforcing loop sending us into the most recent of hundreds of ice ages. In southeast Alaska, this led to the formation of glaciers that filled valleys with long rivers of ice, which carved out their troughs into broad “U” shapes. Eventually the valleys filled up, and the individual glaciers merged into a continent-wide sheet of flowing ice, which rounded off the tops of most mountains except those tall enough to protrude through. When the earth’s orbit changed enough to warm things up about fourteen thousand years ago, these glaciers receded, leaving behind the dramatic topography we traveled in today.
One particular valley (now a fiord), called Tracy Arm, contains the remains of two glaciers: the Sawyer and South Sawyer glaciers. South Sawyer moves rapidly and “calves” icebergs into the fiord, which can become dense enough in places to choke the waterway, as seen in the image here. After very carefully making our way through the crowded ice, we approached Sawyer Glacier. It is somewhat more sedate than its southern sibling, so we were able to approach within a half-mile of the face and see calving and hear the “white thunder” such a large event produces.
While we were near the glaciers, we had the great opportunity to hear from two Wilderness Rangers about the National Wilderness Areas and the Wilderness Act that created them decades ago. Eric and Liz were a fount of knowledge about the area, its waters, wildlife, and visitors. We parted from them in mid-morning and they paddled away towards the glacier around icebergs on mirror-smooth water as we headed down the Arm.
As we sailed down Tracy Arm through the water milky with glacial rock flour, we marveled at the variations in the rocks, with black metamorphic rocks intruded magma, now light-colored granite, that was injected into it along fractures and planes of weakness. This produced a migmatite, or mixed rock, that now provides a dramatic backdrop for the vegetation slowly re-colonizing the recently exposed surfaces, the mountain goats that graze on the vegetation, and the birds and harbor seals that sometimes use the rocks as resting spots.
After an afternoon presentation on glaciers and ice ages that provided more in-depth information, we arrived at a cove filled with deep clear water with only a few icebergs floating nearby. Here we split up into activity groups, with hikers, kayakers, and Zodiac cruisers all able to do what they preferred. The barnacles and tidepool species called out to some, the cool forest under-story called to others, and still others were game for a strenuous hike up to a bog with muskeg ecology and birds on display.
It is interesting to consider the relationships here: it was a major glaciation event, so far in the past, that in fact set the stage for the other activities we pursued today. Without the activity of glaciers, the land and water would look quite different, and the flora and fauna we enjoyed so much might not have been here at all.
Seventy thousand years ago, the earth was cooling off. As more of the earth was covered in snow, it reflected more sunlight out to space, producing further cooling in a reinforcing loop sending us into the most recent of hundreds of ice ages. In southeast Alaska, this led to the formation of glaciers that filled valleys with long rivers of ice, which carved out their troughs into broad “U” shapes. Eventually the valleys filled up, and the individual glaciers merged into a continent-wide sheet of flowing ice, which rounded off the tops of most mountains except those tall enough to protrude through. When the earth’s orbit changed enough to warm things up about fourteen thousand years ago, these glaciers receded, leaving behind the dramatic topography we traveled in today.
One particular valley (now a fiord), called Tracy Arm, contains the remains of two glaciers: the Sawyer and South Sawyer glaciers. South Sawyer moves rapidly and “calves” icebergs into the fiord, which can become dense enough in places to choke the waterway, as seen in the image here. After very carefully making our way through the crowded ice, we approached Sawyer Glacier. It is somewhat more sedate than its southern sibling, so we were able to approach within a half-mile of the face and see calving and hear the “white thunder” such a large event produces.
While we were near the glaciers, we had the great opportunity to hear from two Wilderness Rangers about the National Wilderness Areas and the Wilderness Act that created them decades ago. Eric and Liz were a fount of knowledge about the area, its waters, wildlife, and visitors. We parted from them in mid-morning and they paddled away towards the glacier around icebergs on mirror-smooth water as we headed down the Arm.
As we sailed down Tracy Arm through the water milky with glacial rock flour, we marveled at the variations in the rocks, with black metamorphic rocks intruded magma, now light-colored granite, that was injected into it along fractures and planes of weakness. This produced a migmatite, or mixed rock, that now provides a dramatic backdrop for the vegetation slowly re-colonizing the recently exposed surfaces, the mountain goats that graze on the vegetation, and the birds and harbor seals that sometimes use the rocks as resting spots.
After an afternoon presentation on glaciers and ice ages that provided more in-depth information, we arrived at a cove filled with deep clear water with only a few icebergs floating nearby. Here we split up into activity groups, with hikers, kayakers, and Zodiac cruisers all able to do what they preferred. The barnacles and tidepool species called out to some, the cool forest under-story called to others, and still others were game for a strenuous hike up to a bog with muskeg ecology and birds on display.
It is interesting to consider the relationships here: it was a major glaciation event, so far in the past, that in fact set the stage for the other activities we pursued today. Without the activity of glaciers, the land and water would look quite different, and the flora and fauna we enjoyed so much might not have been here at all.
