1) The cycles of the Universe 

In the Indian mythology, the universe is supposed to go through cycles with each cycle starting with creation (shrishti), maintenance (stithi) and laya (dissolution).  The stithi or maintenance portion of this cycle is called a mahayuga or great period, itself consisting of 4 yugas (sub-periods)- krita, treta, dwapara and Kali. Ishwara (God) is considered "Shristi Stithi Laya kāranam" or the cause of creation, maintenance and destruction. This is beautifully explained in the Bhagavad Gita. 

सर्वभूतानि कौन्तेय प्रकृतिं यान्ति मामिकाम् |

कल्पक्षये पुनस्तानि कल्पादौ विसृजाम्यहम् || 9.7||

प्रकृतिं स्वामवष्टभ्य विसृजामि पुन: पुन: |

भूतग्राममिमं कृत्स्नमवशं प्रकृतेर्वशात् || 9.8||

sarva-bhūtāni kaunteya prakṛitiṁ yānti māmikām
kalpa-kṣhaye punas tāni kalpādau visṛijāmyaham
prakṛitiṁ svām avaṣhṭabhya visṛijāmi punaḥ punaḥ
bhūta-grāmam imaṁ kṛitsnam avaśhaṁ prakṛiter vaśhāt

All beings, O’ Son of Kunti, reach the Parkriti (nature) belonging to me, at the time of dissolution of a kalpa (an era). I send them forth again at the beginning of a kalpa. (Bhagavad Gita 9.7)

Controlling my own Prakriti (nature), I send forth this entire multitude of beings necessarily by the force of Prakriti (Bhagavad Gita 9.8).

The dissoultion of the Universe is called Pralaya in Sanskrit and it symbolies the cosmic sleep when the matter and energy in the Universe resolve into what is known as "Māya", or that from which matter and energy later evolve. Even though the word "destruction" is sometimes used to denote the term pralaya, there is actually no destruction of anything-just resolution into a dormant form. Even our mind, which is part of the Sukshma Shariram or the subtle body, gets resolved into what is called Kārana Shariram or the Causal body. 

2) Kāla Bhairava

Though it is only one Ishwara that is responsible for all the three aspects mentioned above, to symbolize and give form to the dissolution, a form of Shiva called "Kala Bhairava" is sometimes used. "Kāla Bhairava" means the terrifying or all-destroying time, where Kāla means time and Bhairava means terrifying or destructive. 

Time can be the greatest healer and the greatest destroyer, especially of one's ego, which is why the leg-behind-the-head asanas are representative of a sword placed behind one's head to check one's ego.

Kāla Bhairava is often depicted as standing on one leg with Vishnu and Brahma emerging from his torso. The one-leg is representative of the pillar supporting the Universe. So, in that sense, Ishwara, in the form of Kāla Bhairava not only dissolves the Universe but also supports it.

3) Bhairavāsana

Bhairavāsana is an asana that comes in the leg-behind-the-head sequence of asanas in the Ashtanga Vinyasa third series of asanas. Just like the other leg behind the head asanas, the leg behind the head symbolizes a sword to keep one's ego in check.  

In Bhairavāsana, the leg on the ground is planted strong to symbolize the strength of Bhairava. The hand and the foot behind the head both point up symbolizing the uplifted weapons of Bhairava.