Mt Pinatubo Volcano and the Rivers of Ash

I awoke early, stumbling around in the dark so I would not wake my wife, found my epaulets and headset and headed out the door. My flight today was from the Ninoy Aquino International Airport in Manila to the Subic Bay International Airport on Luzon Island Philippines.

Subic Bay Freeport Zone Philippines

The C208 Caravan Amphib was ready to go and because we were “relatively” early the Manila airport was quiet. We didn’t have a long queue in front of us for start-up, taxi and takeoff and so we were airborne in about 20 minutes.

Sunrise at Ninoy Aquino International Airport Manila Philippines

C208 Caravan Amphibian Seaplane

The sun rose quickly and I took off in the bright morning light turning north-west across Manila Harbour.

My agenda for the day was to break a Grand Caravan pilot of all his bad habits. This was going to take all day. (I always say that Grand Caravan pilots are “wheel” pilots but Amphib pilots are “real” pilots.) The most important part about re-teaching “wheel” Caravan pilots how to fly is what I call “situation awareness.” Instead of letting the pilots go into comatose after takeoff, waiting for the tower to hand them off, I ensure amphib pilots are kept busy assessing the immediate post takeoff situation that they are flying into – starting right from “positive-rate-of-climb” gear awareness until reaching “safe altitude.”

Just like “circuits” are the best way to teach takeoffs and landings to a student pilot, the most effective way to teach “gear awareness” on the Caravan Amphib Seaplane is to carry out alternating runway and water landings at an airport that also has a water aerodrome. A pilot’s” gear awareness procedures are really tested when switching from land to sea and back to land again. The Subic Bay airport is a perfect location.

Subic Bay International Airport and Water Aerodrome

Subic Bay International Airport and Water Aerodrome

First, however, we flew past Subic harbour toward the north-west for some “missed approaches at altitude” air work.

Subic Bay was the site of the US Naval Facility in the Philippines

On route we came across a large wide dried up river. I have seen rivers like this below glacial mountains where the gravel and silt washes down every spring for millennium building wide shallow river valleys. But this was not a glacial mountain.

Volcanic ash washing down to the South China Sea


Flying up the river of ash. Mt Pinatubo on the horizon.


Subic Bay seen in the top left of this early morning photo

Subic Bay seen in the top left of this early morning photo

As a seaplane pilot I am always looking at rivers but this one was different. It had very little water and no deep channels. This was not, or never was, a “river” except during a cataclysmic eruption that took place 23 years ago. It is a river of ash. I was very aware of the source of this mysterious river but it was still amazing to visualize the magnitude of the outflow coming up from deep within the earth during the 1991 Mt Pinatubo volcanic eruption.

The ash is so heavy that construction companies are excavating it to build roads up the steep slopes of the nearby mountains.


On June 15, 1991, Mount Pinatubo, just 20 miles (32 km) from Subic Bay, exploded with a force 8 times greater than the Mount St. Helens eruption. Day turned to night as volcanic ash blotted out the sun. Volcanic earthquakes and heavy rain, lightning and thunder from Typhoon Yunya passing over northern Luzon made Black Saturday a 36-hour nightmare. Wikipedia


Mt Pinatubo Philippines

Where were you the day Mt Pinatubo in the Philippines blew?

It wasn’t part of my original plan that morning but since it was part of my larger agenda I decided to explore the possibility of adding a Mt Pinatubo Scenic Flight to our adventure menu. If I flew up the river I should find the source. Right?

Follow the red line to the river of ash.

Google Earth close up of Mt Pinatubo


Following the river of ash.


Mt Pinatubo in the distance

As I flew up the ash river I got distracted by a lake. The rains had to go somewhere and for the most part the water collected in this small lake called Mapanuepe or Lake Pinatubo. Submerged in the 10 meter deep lake are 500 structures including a Catholic church. The steeple and cross protrude above the still surface creating an eerie post apocalyptic image.

Just beyond it, buried in the morning cloud and hidden by rain forest, is Mt Pinatubo.

Lake Pinatubo with church steeple and cross poking through the still waters.


The soft volcanic material is easily eroded by the tropical rains.

In 1991 Mt Pinatubo erupted creating the second largest explosion in the 20th century and 8 times more powerful than Mt St Helen. The result was towering plumes of ash (similar to how Mt Vesuvius was described) and erupting flows of ash and pumice know as Lahars.

“Lahar” is a Javanese word that describes volcanic mud flows. Lahars have the consistency, viscosity and approximate density of wet concrete: fluid when moving, solid when at rest – thus explaining the use of the ash to surface newly built mountain roads.

Heavy rains from Typhoon Diding (Yunya), coincidentally flooding the region at the same time as the volcanic eruption, mixed with the ash and contributed to the massive Lahars floods creating the rivers seen in these photos.

The effects of the eruption were felt worldwide. It ejected roughly 10,000,000,000 tonnes or 10 km3 (2.4 cu mi) of magma, and 20,000,000 tonnes, bringing vast quantities of minerals and metals to the surface environment. It injected more particulate into the stratosphere than any eruption since Krakatoa did in 1883. Over the following months, the aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F) in the years 1991-93, and ozone depletion temporarily increased substantially. Wikipedia

And we wondered what was causing global warming? The most interesting aviation aside was that at least 16 commercial aircraft made damaging encounters while flying with the ash cloud ejected by the June 15 eruption. The encounters caused loss of power to one engine on each of two aircraft. 10 engines were damaged and replaced, including all four engines of one jumbo jet.

The “river” flows down to join with the ocean seen on the right of the picture


Plinian eruptions, also known as Vesuvian eruptions, are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79. The eruption was described in a letter written by Pliny the Younger; it killed his uncle, Pliny the Elder.

Plinian eruptions are marked by columns of gas and volcanic ash extending high into the stratosphere, a high layer of the atmosphere.

Mt Pinatubo pumice created a plume 35 kilometers high opening like an umbrella to form a cloud 249 miles (400 km) across.

The key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions.

Short eruptions can end in less than a day, but longer events can take several days to months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic flows.  The amount of magma erupted can be so large that the top of the volcano may collapse, resulting in a caldera. Fine ash can deposit over large areas. Plinian eruptions are often accompanied by loud noises, such as those generated by Krakatoa. Wikipedia

Close up of a Lahar Valley

This particular Lahar valley is wide and deep without a frame of reference to determine the scale. That is until I spotted a 4X4 vehicle driving deep within the valley floor. Somewhere in this picture is a jeep. See if you can spot it about 3/4 up the valley. I thought I got up early this morning, but this dude must have been driving since 4:00 am to get to this point by the 7:40 am I took this picture.

Climbing up Mt Pinatubo has become an adventure junkie trip of a lifetime and there are many ways to get to the top. Picture yourself hiking or driving up this valley.

Getting to the caldera of Mt Pinatubo is a long hot hike.

My Pinatubo Caldera Lake

A caldera lake has formed in the crater of the volcano. From Google Earth it looks at least 1.1 nautical miles long. A small river drains the overflow. I will have to come back another day to check this out as today the cloud layer is lying low over the caldera. Time to go to work.

About John S Goulet

Air Transport Pilot, consultant, writer, blogger and photographer with 40 years in Professional Aviation.
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