Newfoundland's Bay of Islands Ophiolites

This second installment of IAT Natural Heritage is by Beyond Ktaadn's Mike Jones (IAT North America Alpine Ecologist), Liz Willey, and Marilyn Anions and is excerpted and adapted from their new Eastern Alpine Guide, with photos by IATNL.

Newfoundland's Bay of Islands Ophiolites

It’s only about two hours from the fogbound ferry terminal at Port-aux-Basques up the Gulf of St. Lawrence coast, to the logging roads that lead into the mountains surrounding the Bay of Islands.  There are four mountain ranges in all: broad, ocean-front mesas with enormous alpine tablelands, encompassing little-known but spectacular ranges known as the Lewis Hills, Blow Me Down Mountain, North Arm Hills, and Tablelands.

 

The island of Newfoundland rises to its highest point near the center of the Lewis Hills, at a windswept and lonely dome known as The Cabox.  The Cabox’s westerly vantage takes in the Gulf of St. Lawrence from the Port au Port Peninsula to the North Arm Hills. Several vantage points along the western rim of the Lewis Hills tableland peer down vertically to the ocean, 600 meters (2,000 feet) below.  These vistas are vivid testament that in Newfoundland, spectacular mountain scenery can exist at elevations under 1000 meters.

 North Arm Hills from Cape Blow Me Down 

 

The four mountain ranges can be divided into two pairs at the Bay of Islands, itself one of the most identifiable features on the western coastline of Newfoundland.  The Lewis Hills and Blow Me Down Mountain form the southern bloc (roughly, the area southwest of the city of Corner Brook.)  The northern bloc (northwest of Corner Brook and south of Bonne Bay near Gros Morne) includes the remote North Arm Hills and world-famous Tablelands, which are protected within Gros Morne National Park.  Each mountain supports tens of thousands of hectares of boreal, subalpine, alpine, and serpentine wilderness. It’s possible, for instance, to walk across the Lewis Hills and Blow Me Down ranges - a distance of 44 km (27 mi) from Cold Brook Road, north to the Bay of Islands - without crossing a road.  You will, however, have to cross Serpentine River.

Serpentine Valley, with Blow Me Down Mountain in background

 

The Bay of Islands mountains are unique because they are derived in large part from mantle, the hot, metal-rich sludge that forms the majority of the Earth’s interior mass. In the Lewis Hills, for example, rocks may be observed that represent the boundary between oceanic crust and mantle, which typically occurs 10 km (6 mi) below the surface.  In fact, the Bay of Islands mountains contain one of the best-preserved ophiolites exposed anywhere on the earth’s surface.  Ophiolites are rock sequences that span the contact between mantle and crust.  As such, they contain rocks derived from mantle, like peridotite or serpentine, and rocks derived from crust, like basalt.  Occasionally sedimentary rocks of the ocean floor are also found.

View of Blow Me Down Ophiolite, with Mad Dog Pond in background

 

The Bay of Islands region is also known among geologists worldwide for the incredible, sprawling serpentine barrens.  Extensive exposures of serpentine give the mountains a distinctive, moonscape appearance that is similar only to Mont Albert, Québec and the White Hills of northern Newfoundland; but is otherwise very distinct from every other eastern mountain.  Serpentine outcrops rarely occur in the form of massive alpine mountain ranges the way they do here.

Serpentine Barrens atop Lewis Hills

 

Lewis Hills —  The Lewis Hills form an irregular, flat-topped, steep-flanked mesa 24 km (14 mi) long and 10 km (6 mi) wide, which is deeply indented by giant cirques along its western and southern flanks.  There are few other places in eastern North America where such magnificent alpine scenery is juxtaposed so closely with the ocean.  It only takes one firsthand encounter to become completely enamored with oceanfront mountains.  Other prominent examples are found primarily in Newfoundland, including the Table Mountains, Blow Me Down Mountains, North Arm Hills, Gros Morne, and the Highlands of St. John.

 

 

The Lewis Hills plateau is deeply incised at its western edge by the Lewis Brook glacial valley, which provides access to the southern and western portion.  The eastern edge of the plateau is sharply bounded by the Fox Island River, which provides the southern access point for the Lewis Hills section of the International Appalachian Trail.  The northern slopes are bounded by Serpentine Lake and the Serpentine River, and the western escarpment drops quickly into the Gulf of St. Lawrence.  The steep slopes of the Lewis Hills plateau around 500 m (1,640 ft), and then slope gently toward the high point at the Cabox (814 m; 2,672 ft).

Fox Island River at the eastern flank of Lewis Hills

 

The captivating beauty of the Lewis Hills, as on all of the Bay of Islands mountains, is most evident in the cirques and ravines that adorn the north and south faces.  The most eye-catching, unusual, and remote of these are the ocean-draining sister-cirques of Molly Ann and Rope Cove Canyons, set facing northwest on either side of Mount Barren. Molly Ann Canyon is a downright Rivendell-esque landscape of waterfalls, rivulets, snowfields, and basaltic cliffs, overlooking the ocean.

Molly Ann Gulch, Lewis Hills

 

Rope Cove Canyon, barely a 3 km (1.8 mi) walk across dry tundra to the northeast, could not be more starkly different from Molly Ann Canyon - or any other place on earth. Its headwall is serpentine; its eastern wall is gabbroic and its western wall is apparently a combination of gabbros and basalts.  The contact zone between mantle and crust is in plain view from the headwall of Rope Cove: serpentine, gabbro, basalt, a perfect ophiolite sequence, and a rainbow of colored cliffs.  This boundary between earth's mantle and ocean crust is called the Mohorovicic Discontinuity.  Where the "Moho" is exposed at the surface there are often exposed serpentines, derived from mantle, as well as gabbros and basalts, derived from the crust.

Rope Cove Canyon, Lewis Hills

 

Blow Me Down Mountain — Blow Me Down Mountain is separated from the Lewis Hills by the Serpentine Valley, which is about 5 km (3 mi) wide at this spot. Similar to the geologic arrangement in the Lewis Hills, Blow Me Down’s eastern slopes are primarily ultramafic rock and the central mass is composed of mafic rocks like gabbro. 

Blow Me Down Brook Valley

 

The massif reaches its highest elevation at gabbroic Round Hill (761 m; 2,497 ft). On the south face, Simms Brook Canyon and Red Gulch drain into the Serpentine Valley. On the north face, Blow Me Down Brook plunges over a 150-ft waterfall and through a massive, deeply incised, cirque-like canyon before draining into the Bay of Islands.

Blow Me Down Brook Falls

 

Simms Brook and Blow Me Down Brook Canyon, like Rope Cove and Travertine Canyon, straddle the discontinuity between serpentine and gabbro in their upper reaches, and so harbor an unusual juxtaposition of plants within a small region.

Simms Gulch, Blow Me Down Mountains

 

North Arm Hills — North of Blow Me Down Mountain, the North Arm Hills abruptly rise from the “North Arm” of the Bay of Islands, culminating at the summit of North Arm Mountain (703 m; 2,306 ft).

North Arm Mountain

 

The adjacent subalpine tableland is known as the St. Gregory Highlands or the Gregory Mountains.  North of the height-of-land, Overfall Mountain (614 m; 2014’) provides access to the Overfall, a 300-foot waterfall along Overfall Brook.  The southern face of North Arm Hills - a vast expanse of serpentine at the edge of the Bay of Islands - is visible to boat traffic coming in to the port of Corner Brook and is clearly visible from most points on Blow Me Down. 

View West from North Arm Mountain

 

The very northern portion of the North Arm massif, including the Overfall and the southern shore of Trout River Pond, is within Gros Morne National Park. 

Tablelands —  The Tablelands of Gros Morne National Park are also the northernmost mountains in the Bay of Islands complex.  The Tablelands are smaller than the three massifs to the south, and comprised primarily of peridotite, with a small area of gabbroic rock exposed on the plateau.  They reach their highest elevation (721 m; 2366’) near the center of the massif, which is sometimes referred to as Table Mountain.

Tablelands from Trout River Pond

 

Just east of the Tablelands near the town of Glenburnie is the Pic à Tenerife (Peak of Tenerife; >538 m; >1,766 ft), which has a small, scrubby, open alpine area and a spectacular view.  (It was named by Captain James Cook in 1767, because the sharp-toothed peak reminded him of Tenerife, Canary Islands.)  Just north of the Tablelands, the Lookout Hills rise to a plain of soggy, open tundra.  The Tablelands are within Gros Morne National Park, where the great Winter House cirque on the Tablelands’ north face is probably the best-known landscape feature after Gros Morne Mountain itself.

Northern Tablelands near Woody Point, Gros Morne National Park

 

Geology — All four of the mountains profiled in this chapter are composed, to varying extents, of mantle-derived rocks (ultramafics) and associated mafic and igneous rocks.  Thus they often represent the major components of a full ophiolite suite: ultramafics, mafics, igneous basalts, and sedimentary ocean.  For example, the central one-third of the Lewis Hills, including the Cabox and the Big Level, is composed of mafic (magnesium and iron rich) rock, which stands out in contrast to the eastern third of the range, which is composed of serpentine.  The serpentine area is most accessible in the vicinity of Spring Hill, Wheeler's Brook, and Red Rocky Brook. 

Red Rocky Gulch, Lewis Hills

 

The highlands west of Lewis Brook are mostly basaltic, as are the flanks of Mount Barren. Sedimentary layers extend from the Fox Island River onto the Lewis Hills massif at Rabbit Hill. By comparison, the western portion of Blow Me Down Mountain is largely composed of diorite, an igneous rock, though its western reaches are composed of metal-rich serpentines.  The North Arm Hills are similarly composed, but the Tablelands consist mostly of serpentine.

 

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To learn about the flora and fauna of Newfoundland's Bay of Islands Ophiolites, pick up a copy of Beyond Ktaadn's Eastern Alpine Guide

... and stay tuned for another installment of the IAT Natural Heritage series.