Introduction
Exit Glacier and Harding Icefield trails
Orcas, whales, and pillow basalts

Introduction

Due to a little miscalculation on my part during the planning stage, we arrived in Alaska a few days early for the project.  Kenai Fjords National Park is in south-central Alaska near the town of Seward - just under three hours drive from Anchorage.  Rather than stagnating in a cheap hotel in the city (and we definitely stayed in the very cheapest place I could find!), we drove down to Seward to see modern glacial geology.

Fjords are long, deep sea inlets found in glaciated regions.  Glaciers are large, flowing bodies of ice that form where snow accumulates faster than it can melt away.  The ice gets thicker and thicker, until gravity's steady pull on the massive weight of ice causes the ice to flow like a viscous glob of icing oozing off a cake.  The ice abrades the ground over which it flows, carving deep valleys.

Fjords form when glaciers carve those deep, u-shaped valleys into the rocky earth near coastlines.  After the glaciers melt back a bit, seawater flows into the valley, submerging it and forming a steep-walled cove.  Kenai Fjords National Park has many fjords from glaciers that sprout off the Harding Icefield and flow down into the Gulf of Alaska.  The park is a great place to see modern glacial geology in action!  Just look at all of those glaciers fingering out in all directions from the central ice sheet! 

Exit Glacier and Harding Icefield trails

There are two hiking trails in Kenai Fjords National Park that are readily accessible from the park entrance near Seward:  the Exit Glacier trail and the Harding Icefield trail. 

The Exit Glacier loop is a very easy hike along the glacial outwash to the toe of Exit Glacier.  The trail works its way up a short distance alongside the glacier, as well, where this photo was taken.

(Melania is not actually wearing a wilderness tent.  Dan loaned her his jacket because her luggage was delayed by the airline.) 

Exit Glacier terminates at the edge of the valley.  Melting snow feeds a creek that carries sediment eroded by the glacier as the ice scrapes along the rock.  When the creek opens up into the the valley, the water slows and deposits the silt, sand, and cobbles in a broad plain called the outwash plain.

One can approach the toe of the glacier by hopping over the little rivulets running between the muddy cobbles.  We visited very early in the season, before the winter's thin mantle of snow covering the ice could melt away, so the blue glacial ice and potentially hazardous overhangs were not exposed. 

The glacier cuts through poorly-sorted marine wackes and conglomerates.  The white and brown spots in the rock pictured here are pebbles that were embedded in the gray seafloor mud before the stuff hardened ("lithified") into solid rock. 

The white lines cutting across the rock are quartz veins that formed when the hard rock fractured, then groundwater flowed through the cracks and deposited the mineral quartz. 

The dark streaks on this rock are glacial striations - scratch marks left by the glacier as the ice flowed over the surface. 

There are two types of lines in this rock:  sedimentary bedding and glacial striations.  Sedimentary bedding reflects compositional variations in the layers of sediment as it deposited on the sea floor.  The bands of rock have slightly different colors because some layers contain a little more quartz silt than others. 
Glacial striations, on the other hand, are scratches that cut straight across the surface of the rock. 
One of these features crosses the photo side-to-side and the other crossed diagonally.  Can you recognize which is which?

This is a close-up view of the quartz veins that cut the marine sedimentary rocks along the Harding Icefield trail.  These veins have sharply-defined walls, which means they formed when the siltstone was a hard rock - long after the silt deposited on the ocean floor. 
The white quartz that fills the veins is a mineral made of silicon and oxygen (SiO₂).  The sand grains in the marine sedimentary rocks contain a lot of quartz, too.  It is likely that the quartz in the veins formed when deep groundwaters flowed through cracks, dissolving silica from silt grains in the sedimentary rocks, then re-depositing the silica when the water cooled in the veins. 
If you get a chance to go on this hike, pay attention to the orientation of the veins in outcrop (i.e., not in this photo).  There is a very systematic pattern with two dominant orientations.  The pairing of those two particular orientations suggest the fractures/veins formed as conjugate shears in the same stress field. 

We were unable to go more than a kilometer along the Harding Icefield trail because it was still snowed in.  The trail should be passable by June, but I wouldn't recommend it in early May.

Melania was the first in our group to discover devil's club.  You can see in this photo that the clubs are just starting to bud.  The spines break off once their in ones skin and are quite fine, making them tricky to extract.  Devil's club grows in large patches and usually has big leaves, but not this early in the season. 

The initial ascent from the valley reveals a nice overlook of the toe of Exit Glacier peeking out of its valley (bottom right), as well as the lateral moraine sediments that deposited alongside the glacier when it used to stretch out beyond its current confines.  It's sort of like a bathtub ring visible here about halfway up the picture.


The subhorizontal shelf in this photo is the lateral moraine.  The mountainside below the line is covered with glacial sediment (the lateral moraine), which is a much better place for plants to grow than the rocky ledges above that lack soil. 


There were some interesting conglomerates along the trail. 
The conglomerate on the left consists of large cobbles set in a matrix of fine mud.  What sedimentary environment would drop such large rocks into such fine mud?
The conglomerate on the right also contains cobbles with mud.  The cobbles in this rock, though, are very long because the source rock broke in a platy manner - like slate.


The pebbles in this conglomerate are big at the bottom, medium-sized in middle, and fine-grained at the top.  Geologists call this "graded bedding."  Graded bedding tells geologists that the sediment deposited quickly by a big rush of turbid, sediment-filled water in a submarine landslide.  The biggest pebbles drop out of the water column first, then finer ones later.  Graded bedding also tells geologists the original orientation of rocks when they've been uplifted and tilted (big pebbles were originally on the bottom.) 


When we couldn't get far on the Harding Icefield trail, we retreated and hiked a nice little state park trail to Tonsina Creek.  It was a beautiful day.  The beach was fascinating because the sand was all derived from weathering of phyllite (a weakly-metamorphosed siltstone that breaks into tiny chips).  The hike was easy and the scenery rewarding.

We spent an afternoon hiking in Chugach State Park, too.  The U.S. Forest Service office in Seward was very helpful and knowledgeable.  The ranger suggested we hike the Ptarmigan Creek Trail.  She had hiked it the previous day and so knew that it was dry (i.e., not snow-bound).  It was great advice!


Ptarmigan Creek Trail - Ken and Dan looking over the waterfall

Ptarmigan Creek trail - Ptarmigan Lake was still partially frozen over.  What a beautiful day!

Orcas, whales, and pillow basalts

We took one of the boat tours of the Park one day.  The price seemed a little steep when we signed up, but most things are a little more expensive in Alaska.  We were very impressed by the tour, though, and had no buyers remorse at all.  The people running the boat were very friendly, professional, and knowledgeable.

We even bought the lunch, which turned out to be a really good deal - excellent food (prime rib and salmon) and all you can eat. 


The tour left from Seward Harbor - about a block from our hotel.  Considering the size of the town of Seward, everywhere is within a block or two of the harbor!

Aialik Glacier enters the sea in Aialik Bay.  As the ice pours out of the mountains into the ocean, big chunks of ice break off and splash into the water - a process called "calving."  The ice is constantly popping as it bends and cracks. 


Harbor seals swimming in icy Aialik Bay water.  They're much tougher than I am!  That's salt water, so the temperature is actually below 0ºC (below 32ºF).

Aialik Glacier crevasses - deep fractures in the ice that form as the ice flows unevenly - are clearly visible along the glacier's skyline. 
The glacier's face is a vertical wall because the fracture ice calves easily when the ice meets the water, losing support from the underlying rock while simultaneously experiencing an upward buoyancy as the ice floats on the seawater.


A pod of orcas (killer whales) swam around the boat for a while.  They are extraordinary creatures!

The animals were fine, but the geologic sights were more my style.  In addition to seeing the calving glacier, we also saw two outstanding outcrops of the Resurrection Bay Ophiolite. 

Ophiolites are big sections of oceanic crust (lithosphere) that get pushed up onto the land.  They are pretty rare geologic features and not usually so beautifully exposed.  This cliff consists of millions of lobes of pillow basalt.

The USGS published a geologic map of Chugach National Forest here.
There is a draft geologic map of Kenai Fjords National Park here.



Bird poop highlights the bulbous basalt pillows.  Pillow basalts form when mafic lava erupts on the sea floor.  The water is cold, which causes the blob of magma to crystallize quickly into a "pillow."  As more lava escapes to the earth's surface, it must flow around the old solidified pillows, quickly cooling to form new pillows. 

Bird poop highlights the shape of the basalt pillows while the birds stand for scale so you can see how big these pillows are. 



The pillows have rounded tops and bottoms that taper more or less to a point.  This is the normal shape of fresh basalt pillows, so geologists know that these pillows are in their original orientation (not tilted or overturned).

The uppermost layer of ophiolite sequences is made of pillow basalts and deep water oceanic sediments.  The lava needs some way to get from deep in the earth up to the surface.  Underground lava (we call it "magma" until it reaches the surface) flows up through fractures in the oceanic crust.  A lot of the magma freezes solid in the fractures, forming tabular bodies of basalt called "dikes."  The dikes can be very closely spaced because, once an old fracture is "healed" with solidified basalt, the oceanic crust continues to break as it is pulled apart, forming new fractures that fill with magma, ... that cools to form new dikes, and the process continues.  Imagine breaking a dish, gooping some superglue into the fracture to mend it, then breaking the dish again, over and over again many times (as has happened with my favorite coffee mug).  The closely-spaced swarms of dikes in ophiolites are called "sheeted dikes."


Small tree roots serve as a scale for these sheeted dikes that were exposed along the shoreline on our tour.  There is a little cross-cutting evident if you follow individual dikes up from the bottom of the photo to the top. 

A new take on the origins of sheeted dikes is posted in this paper.

On to survival training photos